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Micro Micro Coverphoto: Allan Hansen, Denmark

MegaBook Megazine

Contents

Preface ............................................................................ 5 Summary......................................................................... 7 Introduction ....................................................................9

First edition 800 copies

1.

MST for consumers and health

Editor-in-chief Philip Broos

The art of atomising .....................................................................12 Slow grower hunted down at high speed.....................................20 Testing freshness with gold-tipped DNA......................................30 The taming of the fibril.................................................................36

Colophon MicroMegaBook published in 2010 by the MicroNed Consortium The Netherlands ISBN 978-90-816296-1-4

Editors Richard van der Linde Fred van Keulen Contributors Marion de Boo Hans van Eerden Henne van Heeren Joos van Kasteren Richard van der Linde Bennie Mols Ruud Overdijk Tjeerd Rijpsma Arno Schrauwers Translators Margaret Clegg Marcus de Geus Graphic design/Image processing Cok Francken MultiMediaServices Printed by DeltaHage BV The Hague Illustrations The illustrations in this book are protected by copyrights. However MicroNed does not claim own the copyrights to every image that has not been attributed by way of an image credit. If MicroNed unintentionally has infringed on your copyrights, please get in touch with the editor-in-chief, philip_broos@compuserve.com

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MST in process industry

Microreactors promise revolution................................................46 Micro coriolis sensor for minute mass flows................................54 Ribbed straws increase water treatment capacity.......................60 Milk powder from a print head..................................................66

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MST for high-tech industry

Faster, smaller, more accurate inkjet printers . ............................74 Improved micromilling machine ..................................................82 Smart construction stops components bouncing.........................88 Self-assembly for microsystems....................................................96

4.

MST in space

A satellite swarm as radio telescope..........................................106 Pin-point cooling.........................................................................116 The first autonomous solar sensor.............................................122 Innovative microthruster for Delft microsatellite.......................128

5. 6.

MicroNed achievements..............................................136 Beyond MicroNed........................................................144 Appendices..................................................................151 3


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Preface Micro System Technology (MST) is an extension of a technology called Micro Electro Mechanical Systems (MEMS) that arose in the late nineteen sixties. MEMS focuses on components while MST is geared more to complete systems notably by combining IC technology (electronics) and miniaturised conventional technologies like fluidics, optics, chemistry and biochemistry. MST is an enabling technology with wide applications and sets out to diminish scale so that systems can be faster, more sensitive and cheaper. Microsystems, like accelerometers, microreactors, lab on chip devices, etc, can be more readily incorporated in equipment because of the high density of functions and make such equipment more reliable, safer, more energy saving, more mobile and smarter. A feature of MST is not only the extremely small dimensions but also the multidisciplinary approach to the design and integration of the many functions in a single system. Dutch MST landscape in 2003 Internationally, manufacturing industry saw a clear trend in 2003 with MST activities expanding from electronics into other disciplines like mechatronics, robotics and embedded systems, where new applications and technologies were researched, developed and applied. Traditional mechatronics users (like ASML, Demcon, Bronkhorst High-Tech) began focusing on integrating MST in their product portfolio. Companies in the process industry (food and chemicals) and the aviation and space industry began to see the opportunities offered by MST as well. The Netherlands perforce followed the trend towards industrial integration so as to raise the national level of MST to an international high standard and to consolidate and keep its position in the field. If the Netherlands was to count in the 4


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MST arena, interdisciplinary collaboration between knowledge institutions and business and industry had to be vigorously accelerated was the opinion of a group of academics and industrialists. Employment in the Netherlands relating to MST was estimated at 2,870 people in 2003. Most of them worked in more than a hundred private enterprises1. The global market for MST according to Nexus and Mancef was conservatively estimated at around 12 billion dollars (2005), with an estimated growth of 10-20% per annum. The market position of the Netherlands for MST was considered to be good for the Life Sciences sector (AKZO, DSM) and the Biomedical sector (Philips), and strong in the Agro/Food sector (Friesland Campina, Unilever) and for the high tech equipment sector (ASML, Océ, Fei etc.). Major research programs Around 2000 the government launched the ICES-KIS 3 call, better known later as the BSIK-call. The idea was to create a widely based national incentive programme with which the Netherlands would strengthen its base for the future. Micro and nano technology were focus points of this programme. In response to the call Professor Paddy French and Professor Fred van Keulen of Delft University of Technology submitted and an expression of interest in 2001. This primarily Delft oriented expression of interest was the first step of MicroNed. The immense effort and help provided by the MST entrepreneur Cees van Rijn ensured that there was a very substantial industrial participation in the ulti1  source: Innovatieverkenning Micro Systeem technologie; rapport

EZ 03141, 2003, a report assessing innovation using MST published by the Netherlands Ministry of Economic Affairs

mate MicroNed application. The participation has been a significant factor in the success of the implementation of the MicroNed programme. The partners that associated themselves with this initiative and helped to set up the initial MST consortium, had very diverse backgrounds: industrial and academic, electronics and the food industry, health care and mechatronics etc. All of them were convinced that it was high time to put MST in the Netherlands on the map. Only a coordinated effort was deemed capable of bringing activities on the Dutch MST front up to the highest standard and of keeping them there for the long term. This vision aligned very well with the EU Lisbon agenda launched shortly before, with an ambition for Europe to be a world leader in the field of innovation and knowledge transfer by 2010. On top of this the Netherlands government said it wanted to ensure that the Netherlands would be one of the leading three European players in this field. Major research programmes were launched to live up to these ambitions, for instance the EU’s Sixth and Seventh Framework Programmes and the Netherlands BSIK programme. MicroNed started with 32 participants, the number later rising to 60. Out of a total investment in research and collaboration in the field of MST of €56 million, a subsidy of € 28 million was awarded under the auspices of the BSIK. MicroNed became a consortium of companies and knowledge institutions that brought together knowledge, funds and research efforts. MicroNed had a mission to achieve a market-driven, dynamic and sustainable public-private knowledge infrastructure in

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the field of MST, which was intended to form the basis for new product-market combinations. The MicroNed programme thus built a bridge between fundamental modelling, system design, manufacturing technology, and the application of MST technology, in other words running and reinforcing the gamut of the entire knowledge chain. The composition of the consortium was chosen in such a way as to represent the complete chain of knowledge from first principles to commercial, applied research. As a result MicroNed has facilitated contacts between the (technical) universities, knowledge institutes and many specialised knowledge-intensive companies and major application oriented industries. A number of examples of the result of this collaboration are presented in this book along with new opportunities that have arisen on the basis of the experiences gained. Professor Fred van Keulen November 2010

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Summary At the beginning of the 21st century the Dutch microsystem sector was facing a number of obstacles that were hampering the industrialisation and commercialisation of these systems. MicroNed, a public-private partnership of small and large companies, institutes and universities, was created to surmount these obstacles. The aim was to set up a dynamic and sustainable MST infrastructure to improve the competitiveness of the Dutch industry by connecting the elements of the supply chain, by linking these with international activities and strengthening and disseminating MST knowledge. MST is an enabling technology, thus the value is rather in the final enabled product and its application. The R&D projects in the MicroNed programme thus concentrated in general on complex and cross-domain MST systems for future products. This required multidisciplinary teams. A diverse group of scientists and high-tech entrepreneurs were brought together and created an environment in which mutual understanding between project partners from science and industry could evolve, leading to close and sustainable collaborations. Even though the research often took place at scientific institutes, industry’s participation was essential both as a participant in the R&D and as a guide in the transformation from the laboratory stage to the pre-commercial product and in helping to focus minds on potential applications. Collaboration between science institutes and private enterprises has improved enormously as a result. Mutual understanding of interests has grown, as well as acknowledgment of the position and needs of others. This is confirmed by the growth in the number of participants in MicroNed which started with 32 6


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partners and grew to 60 partners and users. The active participation of industry meant that ideas and concepts went beyond the research phase and were taken a step forward to marketable products. In five years’ time, the MicroNed partners realised over forty new or improved products and processes, and filed almost twenty patents that will lead to new commercial activities. Ten spin-off companies trace their roots back to the MicroNed programme. The MicroNed partners have also come to form the backbone of the new Microfluidic cluster in the MinacNed programme. The space-oriented partners of MicroNed will together contribute to a new space mission (OLFAR), and the successful activities of MicroNed are anchored in the new NanoNextNL programme. MicroNed has also been successful in the training and education field. About 80 PhD graduates and many more MSc graduates were trained through MicroNed and many of them have found their way into companies in the Netherlands and abroad, while several have continued as postdocs at Dutch universities. The MST knowledge generated has been anchored by new MST professors and through MST master and bachelor programmes. Dissemination of the results was a major goal of the programme which is why MicroNed launched the MicroMegazine science magazine in 2009. Many of the scientific results were communicated to an extended audience of over 2000 subscribers. The magazine is highly valued by the MST community in the Netherlands. A second important outlet for the results was the Netherlands MicroNano Conference in 2009 which attracted 550 participants, a third of them from

industry. The strength and importance of both initiatives is demonstrated by the plans to continue them after the end of the MicroNed programme. Over the years several of MicroNed’s commercial partners have shown significant growth, in several cases as a direct consequence of a switch to more value-added products, enabled by MicroNed activities. MicroNed partners initiated new R&D networks which have enlarged and reinforced the value chain of MicroNed partners and of organisations outside MicroNed. Many new project ideas were generated, leading to numerous new projects. Some of them are within the MicroNed programme, but many take place outside the programme, but within the MicroNed community, thus generating dissemination of MST knowledge and expertise. After the Mid-Term Review, flexibility in the execution of the R&D programme and performance monitoring were introduced so that all developments could be followed and steered. Moreover, successful activities were supported by Auxiliary Projects, fourteen of which were launched in the 2008-2009 period. This turned out to be the start of strong clusters that in many cases reached beyond the work package and cluster boundaries of the programme. Such clusters can be seen in the domains of space, microfluidics, jetting, sensors and diagnostics, each well-anchored in the NanoNextNL programme.

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fits very well into the Dutch industry’s strengths, its expertise and track record in equipment manufacturing, and its home market for the agricultural and process industry. In all those markets MST will act as an enabler for new processes and products. Although the complexity of the technologies and their applications seems to call for large and broadly oriented groups, results can only be achieved by ambitious and focused teams of world stature. To obtain a meaningful position one needs momentum, to have an impact on fast-changing markets and technologies, one needs flexible organisations. Balancing these seemingly conflicting demands is the real challenge. The answer lies in the concept of an open and dynamic ecosystem, for which the MicroNed programme laid the foundations.

As to the future of MST in the Netherlands, besides its economic value, it is envisioned that MST will play a decisive role in tackling the grand challenges of the 21st century such as energy, health care, healthy food, clean water, material scarcity and an ageing population. This 7


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Introduction At the beginning of the 21st century in the Netherlands there were obstacles to the growth of business activities relating to microsystem technology (MST) and the creation of a world class, sustainable knowledge infrastructure: i

Knowledge generated locally and nationally was used little and few MST products went on to be developed further or actually produced.

ii Knowledge relating to MST was poorly differentiated in relation to that abroad. iii Dutch players had no great strength in the chains that counted as strong internationally. iv Major (or minor) Dutch companies with potential interest had no need, urgent or otherwise, for MST, being insufficiently familiar with the opportunities MST offers. v Dutch initiatives were small scale and fragmented. Lack of common goal meant that collaboration between user and knowledge chains barely got off the ground, if at all. vi A lack of entrepreneurial input prevailed and there were few start-up companies in the MST sector. vii No coordinated MST training programme existed. viii The supply of good, specifically science-oriented, students was limited.

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ix The great lack of production facilities for small series resulted in huge start-up costs. MicroNed mission and goals MicroNed was founded to resolve the aforementioned obstacles. MicroNed’s mission was worked out in greater detail in ambitious goals: • To set up a dynamic and sustainable MST infrastructure; • To improve the Dutch industry’s competitive position by connecting those who used MST and those who had the knowledge of MST and linking them to international MST developments; • To strengthen and disseminate fundamental and multidisciplinary knowledge. In consultation with a government appointed advisory committee these ambitions were converted into the following main goals1 for the purpose of accountability: a) To set up and maintain a dynamic, sustainable knowledge infrastructure in the field of microsystem technology. This is necessary to retain and extend the competitive position of the knowledge intensive microsystem companies and the knowledge institutes in the Netherlands. At the same time this will serve as a major boost to the further development of innovative MST services and products. 1 

Source: Nulmeting MicroNed, dd. 01-05-2005

b) To consolidate the fundamental and multidisciplinary knowledge in the field of microsystems through the entire knowledge chain. c) To provide knowledge and structured research facilities to bridge the gap between laboratory innovation and the commercial application of MST. d) To set up and extend training course and programmes in the field of microsystem technology at different levels (bachelor, master, PhD, postdoctoral and industrial). e) To create spin-off research to guarantee long-term response to new developments and to enable new partnerships. f) To lay the basis for new commercial MST based activities, for one thing in the form of high tech spin-off companies. g) To create a centre for MST in the Netherlands.

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Chapter 1 deals with the scientific results in the consumer and health industry addressing important societal topics like healthy food, the early detection of tuberculosis, food freshness detection and medical inhalers. The results from the process industry are to be found in Chapter 2 which deals with the industrialisation of MST in the form of ultra sensitive flow sensors, food production technologies, water purification and ultra safe chemical plants. Concrete examples in Chapter 3 explain how MST can support and improve the high tech industry using micro fabrication, (ink)jet technology, micro assembly and micro grippers. Finally the progress of MST for space applications, pushing the limits of this technology, are presented in Chapter 4. The achievements of the MicroNed programme (industrial, scientific, educational and societal) are summarized in Chapter 5. Here the connection is made between the expectations and promises at the start of the programme on the one hand and the results six years later. Finally, Chapter 6 takes a peek into the future of MST in the Netherlands, embedded in a global context.

Milestones and key performance indicators were defined to ensure that the main goals were measurable. These were bundled in three categories: scientific, economic and societal deliverables. Structure of this book This book presents the successes and lessons learned from the MicroNed programme. The first chapters of the book present an overview of the main results of the programme and were first published in MicroMegazine, MicroNed’s science magazine in 2009 and 2010. 9


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Part 1

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MST for consumers and health

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(PHoto: Ruben Schipper)

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The number or asthma patients in the Netherlands is about half a million, and COPD patients number about 300,000. Some of them use an inhaler on a daily basis to take medication that opens their airways and relieves the constricted feeling in their chest.

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The art of atomising

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Innovative inhaler by Medspray delivers medication made to measure About half a million people in the Netherlands suffer from asthma, and another 300,000 are COPD patients. Existing medication can come with severe side-effects, because using a puffer to get the dose just right can be very tricky. Enschede-based technology company Medspray is developing an innovative atomiser for use in inhalers that can produce exactly the right size of droplets to optimise the dose of any medication. The French perfume industry has also shown an interest in the Dutch atomiser wizardry. The 2-jet atomiser by Medspray ensures that a puff of perfume stays airborne much longer than can be achieved with conventional atomisers. By Marion de Boo

Many medicines offering relief for constricted airways are available in various application forms. Less than ten percent of the active

Medspray are a young and innovative company developing medicinal inhalers and the atomisers that go into them. Its eight employees are housed in a cyclamen red cube at the Business & Science Park in Enschede, a place where a lot of knowledge in the fields of microsystem technology and nanotechnology is gathered. Medspray works in close collaboration with its neighbours at MESA+, one of the world’s largest nanotechnology institutes, and with the Physics of Fluids department led by Professor Detlef Lohse at Twente University. One of the devices developed by Medspray is a new type of atomiser for the medication that ­asthmatics need to inhale to widen their airways when they suffer an attack. The medication helps to relax the chronically constricted muscles surrounding the upper bronchi so patients can get more air. “Conventional inhalers manage to get only about ten percent of the medication to its target”, Medspray product designer Ir Wilbur de Kruijf explains. “About ten percent of the required dose gets left behind in the device, and no less than 80 percent ends up in the mouth and throat.” If the patient then swallows the medication, it will enter the bloodstream via the stomach. A common asthma drug like

Salbutamol when swallowed can cause severe palpitations, insomnia, and dizziness. The prototype of the Medspray atomiser achieves the same airway-relaxing effect with a drug dose that is reduced by 80 percent. “This means that the patient swallows much less of the drug and suffers fewer side-effects”, De Kruijf says. The trick is to get the asthma relief drug deep enough into the airways, but not too deep into the lungs, because that’s not where the convulsed muscles are. After lengthy experimentation Medspray has designed an atomiser that produces a highly homogeneous aerosol. The droplet size is uniformly distributed, and the particles have been made exactly the right size to get the medication in the right spot.

ingredient arrives at the right spot in the lungs with most of these inhalers. Most of the medication gets swallowed and can then cause side-effects that include palpitations, shaky hands, and fungal infections in the patient’s mouth.

The current types of inhaler cannot be used by children without a spacer. The aerosol is first sprayed into the spacer, after which the

Clinical study Initial clinical studies using a prototype inhaler for Salbutamol took place in 2006 at the University Medical Centre in Utrecht (UMCU). De Kruijf: “The clinical research at the UMCU compared three average droplet sizes, of 4, 5, and 6 micrometres. The 6

child inhales at its own pace.

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The location at which the droplets of medication settle inside the lungs is decided mainly by their size. The best location for resolving the active ingredient into the lung tissue varies according to the complaint: medication to open up the airways of asthma patients should reach mainly the upper parts or the airways, whereas antibiotics should be distributed throughout the lungs. Administering insulin through the same mechanism is now being considered, as it (Photo: Eric Brinkhorst)

will then enter the blood stream through the alveoli in a matter or seconds.

At the University Medical Centre Utrecht research has shown that the soft aerosol produced by the Medspray inhaler is five times as effective as the aerosol produced by standard inhalers.

Clinical research has shown that droplets less than one micron in size will be expelled as a patient exhales, whereas droplets larger than eight microns will be deposited in the mouth and throat. In this way most of the medication misses the target location (the lungs) altogether, only to cause unwanted side-effects where it does end up. All in all, a lose-lose situation. The Medspray atomisers create an aerosol with 86 percent of the droplets in the useful 5 to 7 micron range, so practically all the droplets manage to reach their proper destination. Aerosols from conventional atomisers produce most of their droplets outside the useful range.

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micrometre droplets turned out to produce the best airway relaxation, from which the conclusion was drawn that those droplets had reached the right area, at the upper end of the lungs. Theoretically, even larger droplets of 7 or 8 micrometres could also reach the right spot, but more of those would get left behind in the mouth and throat, and that would lead to more side-effects.” The patients participating in the study came to the hospital four times to test inhalers dispensing three different droplet sizes, plus a placebo. The patients received a dose each time, after which their lung performance was tested. Fifteen minutes later a second dose and another lung test followed. The prototype of the new inhaler emerged from the test with very good results, as it achieved the same effect as the conventional inhaler (type pMDI, an aerosol can) but using only 20 percent of the conventional dose of medication. De Kruijf: “Our customer, a pharmaceutical company, intends to market the device in 2012. We hope it will be a huge success. In the meantime we have found some more customers.” Milk and beer Medspray develops its atomisers using microtechnology and nanotechnology. The company makes silicon chips with small, very accurately defined holes. If a liquid is pressed through the holes of the atomiser, jets are created that break up into droplets of equal size. De Kruijf: “The start of our company was a typical case of technology push. Both founding members of Medspray had already gained earlier work experience with very fine filters that were used for example to filter bacteria from milk or beer. A liquid pressed though such a filter turned out to produce a fine mist of very uniform droplets, raising the question of how that could be put to practical use. It’s easy to think up all kinds of different applications, including fuel injection, printers, or powdered milk. Using the principle for inhaling medication appeared to offer the best chance of success. We spent four years making prototypes that really worked.” From a jar, De Kruijf shakes a few minute pieces of silicon into the palm of his hand.


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“These are the chips we build into plastic mouthpieces. When you look at the mouthpiece, you can see the small, dark rod inside. When you squeeze a liquid through it, it produces a very fine aerosol, with droplets measuring about 5 to 6 micrometres. We can adjust the size of the holes to make the aerosol more or less fine.” The chip contains hundreds of holes 2.5 micrometres across. The holes are etched into the silicon nitride layer of the wafer with extreme precision, just like in computer chips, in the cleanroom of MESA+. High-speed camera MicroNed has been funding part of the background research for the past three years, together with Twente University. The Physics of Fluids department has a super fast camera that can take pictures with an exposure time of one millionth of a second. De Kruijf: “If we are to optimise our designs, we must first have a better understanding of the things that go on at the microlevel. The textbooks tell you how a Rayleigh droplet distribution forms, but it is still exciting to see it happen with your own prototypes.” “Detlef Lohse’s group has lots of experience with high-speed cameras”, Medspray co-founder Ir Jeroen Wissink adds. “One of the machines they built is the Brandaris camera, named after a well-known and ancient lighthouse in the Netherlands, that could be used to observe very small physical phenomena such as the creation and vibration of liquid bubbles, or the flashes of light produced by a shrimp, which got them a publication in Nature.” Ir Wim van Hoeve, a doctoral student whose thesis was supervised by Professor Lohse, has managed to capture images showing the aerosols of several prototypes of Medspray’s medication atomiser using a camera setup he developed especially for the purpose. A complicating factor in the design of a camera setup like this is that in order to photograph something very small you have to be really close to it, but on the other hand the distance needs to be big enough to allow the droplets to be fully formed and atomised. In addition there is the speed of 25 m/s at which the liquid jets whizz past, which calls for a special kind of light source in the camera setup if it is to be capable of capturing anything.

A jet of liquid will break up into evenly sized droplets according to the Rayleigh principle. The diameter of each droplet is twice the diameter of the atomiser.

The Medspray atomisers are manufactured at the MESA+ Institute

Using lithography and etching techniques, the Medspray design of the

for Nanotechnology of the University of Twente using manufacturing

atomiser is transferred thousandfold onto a silicon wafer.

techniques borrowed from the semiconductor industry.

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When the wafer is completed, it is cut into over a thousand minute chips. This Gandalf atomiser features hundreds of small holes, each only 2 micrometres in diameter.

Different designs for the ideal atomiser. Finding the ideal mixing duct (mouthpiece) is not as

The camera features special flashlights that deliver very bright nanosecond flashes”, says researcher Ir Wietze Nijdam of Medspray. “The camera has to catch the droplet standing still at exactly the moment when it becomes detached from the jet as it breaks up. If the picture exposure time is too long, all you get is a blurred line, which is no use at all.”

simple as it looks. The idea is make the air flow fast when it passes over the atomiser chip, so the droplets become evenly distributed. In the patient’s mouth on the other hand, the airflow needs to be slowed down to prevent turbulence in the aerosol, which would prevent the medication from reaching its destination in the lungs. Research by Medspray has shown that these opposite requirements are very difficult to model in computer software.

The holders with the still loose atomiser chips are clicked in position in the mixing duct.

Final assembly of a test batch. The atomiser chips are placed into their plastic holders under a binocular viewer. This is still done by hand, but Medspray is working with IMS Almelo to develop an automated assembly machine.

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Black box By now droplets of various sizes have been captured. The data have been processed into a model that can be used to predict how droplets of various, more or less viscous liquids will behave. Van Hoeve used the picture to make simulated videos of a few hundred images each that show exactly how the droplets are formed. “We would really like to know for example how quickly the droplets coalesce”, says De Kruijf. “Coalescence needs to be prevented, for it results in larger droplets and a less homogeneous spray. If it happens right at the start, there is nothing we can do about it, but if the droplets don’t start to coalesce until further along, we might still be able to do something about it. We could design a different type of mouthpiece that would change the way the product mixes with the surrounding air. Thanks to the use of the camera we were able to continuously improve our prototypes even further.” “Until recently the aerosol was like a black box to us, but thanks to the high-speed camera we are steadily gaining more insight”, Wissink says contentedly. “It will enable us to deliver custom solutions to customers in the pharmaceutical industry. Without MicroNed we would never have managed to investigate such fundamental matters in such detail with our partners at Twente University. The project cost us a total of € 650,000, with SenterNovem paying half and we the other half.” Inhaling insulin “Each medicinal application can have its own optimised spray”, says De Kruijf. “As I said before, once the aerosol is breathed in, the particle size determines whether it is deposited in the upper or lower parts of the lungs. The smaller the droplets are,


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the deeper they pass into the lungs. Larger particles tend to ‘fly off the road’ sooner as they travel through the increasingly fine branches of the lung tubes.” Asthma relief medication shouldn’t travel farther down than the upper airways, or it will end up too deep down in the lungs, where it will pass into the bloodstream. This is why the slightly larger particles – about 6 micrometres – are the best suited for treatment. Smaller particles of 2 to 4 micrometres can enter the bloodstream via the alveoli. Such fine droplets could for example be used to administer insulin effectively through inhalation, so syringes will no longer be needed. Medspray has developed an inhaler based on the principle of the SHL injection pen together with a Swedish partner, Scandinavian Health Limited. The pen has a medication reservoir and a syringe for injecting insulin directly into the body. The pen needs to be primed, and then when the button is pressed, it releases a preset dose of medication. The idea is to replace the needle on the pen device with a Medspray atomiser and so enable patients to inhale the insulin. De Kruijf: “Perhaps at some time in the future we will even be able to use inhalers to administer painkillers, which cannot yet be inhaled because they need to be applied very carefully.” Continued development Medspray has already amassed five families of patents. The company is working with German and Swedish partners to promote the chances of rapid market launch. Medspray not only develops the atomisers, it has also undertaken to handle the production. The partners are developing the dosing system and the plastic parts of the medical aids. The market introduction of the first inhaler, scheduled for 2012, will be preceded by a long period of medical and pharmaceutical tests. “Even more so because silicon technology is still a novel concept in the pharmaceutical industry”, De Kruijf says. The technology was developed one step at a time. How many holes does it take? How thick should the layers be? How big should the holes be? How do you prevent the droplets colliding once they are formed? How do you keep the droplets evenly distributed in the air? Medspray has built its own aerosol lab with

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In a conditioned area the silicon atomiser chip is lit by a laser. The tiny piece of silicon transfers the heat to the plastic, which then melts around the chip to produce a perfect liquid-proof seal.

Measuring droplet size distribution at Medspray. The aerosol can be measured using what is known as an NGI, a Next Generation Impactor. The metal instrument, which represents the human lung, distributes

This innovative inhaler is based

the aerosol among a number of dishes. The smaller the droplets, the

on an insulin injection pen.

further they manage to travel inside the instrument.

The syringe has been replaced with a mouthpiece and a Medspray atomiser. A spring-loaded mechanism meters the right amount of liquid medication from a

During the clinical tests of Medspray’s 0019 atomiser at the UMC in Utrecht in 2006, asthma patients were administered Salbutamol, which widens

reservoir. The

the airways. The test

dose can be adjusted by the

results showed that the

patient, which is important for diabetics,

medication was effective

who need to set the right dose based on a

in a dose only one fifth of

reading.

the original, so only 20% of the drug would ensure the same result as before.

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pump

Bronchodilation

3.45

fev1

3.4

3.35

3.3

3.25

3.2

0

10

20

40

80

nozzle-chip Results of the clinical study performed at the UMC. The airway-

mix channel

relaxing action of the droplets from the Medspray inhalers is significantly better than the placebo’s performance. The readings

The Medspray inhaler used for the clinical tests consists of a pump bottle, a

show the FEV1, the volume of air a patient can exhale in 1 second.

mouthpiece/mixing duct, and an atomiser chip.

Ir Wim van Hoeve of the Physics

equipment to measure the size of the droplets in the medication spray. De Kruijf: “When we produce droplets, they are all practically the same size; the bandwidth is very narrow. However, some droplets will coalesce and in some cases even triple-sized droplets can be formed, so the aerosol is not 100 percent uniform, but it has a much narrower distribution than can be produced by existing techniques.” With existing atomisers designed to produce droplets of say, 5 micrometres, the actual droplet size varies from 1 to 25 micrometres. A Medspray mouthpiece designed to make droplets of 5 micrometres will actually produce droplets that vary in size from 4 to 6 micrometres at most. The geometrical standard deviation is 1.3. The viscosity of the medication has little or no effect on the droplet distribution. Built-in chip Manufacturers of inhalers cannot just use a production line robot to assemble the minute chips produced by Medspray so a plastic mouthpiece is supplied with the chip bonded in place. De Kruijf: “Designing such a mouthpiece seems simpler than it is. There are many small details that make it a complicated matter. One of the main problems is deflection of the droplets in the airflow. If the shape of mouthpiece on the prototype is only slightly different, up to 30 percent of the droplets will get left behind in the device, and only 70 percent of the medication will get atomised rather than 90 percent. We made many dozens of different mouthpieces before we had optimised the mixing ducts.”

of Fluids group at the University of Twente studies the breaking up of the droplets in Medspray atomisers. This part of the research comes under the MicroNed project. The special equipment produces a hundred images per second, each with an exposure time of one millionth of a second, producing over a terabyte of video data in the past two years alone.

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The mouthpiece must be designed to maximise the airflow over the chip and so create droplets of the right size, leaving as little of the medication behind as possible. On the other hand, once the liquid enters the patient’s mouth, the velocity of the droplets should already have dropped sufficiently to prevent too much of the medication being left behind in the throat. A different kind of challenge, according to De Kruijf, is to get as many chips from a single silicon wafer as possible, so the cost price can be kept as low as possible. Around the holes is the layer of silicon nitride,


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which is currently half a micrometre thick. If the layer could be made even thinner, the resistance offered to the liquid would be even further reduced. This would allow the device to use a lower pressure to produce the aerosol, or to atomise sticky, viscous liquids at low pressure. The higher the pressure, the more expensive and complicated the nozzle needs to be. De Kruijf: “We would prefer to make our atomiser technology fit the design of the existing devices, because the current glass containers have been exhaustively tested, do not react with the medication, and extend the medication’s shelf life. In short, we like to deal with proven technology.” Acceptance tests Several thousands of prototypes of the new inhaler will be tested by the acceptance authorities in the next few years for various types of medication. A designer needs to be able to prove that each part used in packaging for medicinal use contains no materials that could react with the medication. The inhaler will be constructed without the use of any adhesive, and the plastics used in the production must be approved for pharmaceutical use. This why the chip around which the entire design revolves is first held in the correct position by a plastic insert and then heated by a laser. The hot silicon will cause the adjacent plastic to melt sufficiently to solidly embed the atomiser after cooling. “We devised the entire process by ourselves”, De Kruijf says. “I had to reject at least fifteen different designs, with hundreds of samples being tested for each design. It is very satisfying to be able to go on tinkering until it just works. Inhalers will become more user-friendly. We still see cases in which some medicinal inhalers that pass the standard test in a lab fail to work properly in practice because people breathe in too gently or too strongly. Our own design is much less affected by this and that makes it much more user-friendly. If you consider the fact that in the Netherlands alone half a million people suffer from asthma, I expect this design to do very well indeed.”

Perfume Medspray has also become active in the perfume and cosmetics market. “We were picked out by a French agency specialising in microtechnology and nanotechnology”, De Kruijf says. “Their research into our atomisers had shown that our atomiser produces just the right kind of puff, but instead of a straight jet they wanted a jet that comes out at an angle of about 60 degrees, so you can apply the product from the correct distance to exactly the right patch of skin, on your wrist or behind your ear, for example.” Medspray developed a 2-jet atomiser with the ideal spray that exactly matched the perfume manufacturer’s requirements. Basically there are two things you can change in a 2-jet spray prototype -the diameter of the ducts and the angle at which the two jets meet. Two jets at right angles immediately produce a wide cloud. If you select a slightly smaller angle, say 75 instead of 90 degrees, the spray will have a higher forward velocity and a smaller exit angle. In other words, the atomised cloud will form a slightly narrower cone. The duct sizes were also varied to see which size would yield the best result when pushing the perfume dispenser’s pump. De Kruijf: “We applied for a patent on the production method for these atomisers. We hope to be able to market the principle and we are currently discussing terms with a perfume producer. We are also engaged in feasibility studies.” The main challenge, apart from designing and producing the atomisers, lies in minimising the cost of production. As with the medical applications, a low cost price is essential in the perfume market to reach a wide enough customer range, even with the perfume costing close to 100 euros in the shops. De Kruijf: “MicroNed supported this research because very little was known in the Netherlands about the microlevel aspects of the 2-jet atomiser principle and all the variables you can optimise when developing a 2-jet atomiser. In that regard this is a pioneering project.”

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Detail of the test setup. The Medspray atomiser chip is fixed in the tip of a thick needle. The camera is attached to a microscope objective.

For more information, please contact Ir Jeroen Wissink, e-mail wissink@medspray.nl or

The atomiser chip, with a row of 13 apertures, each 10 μm in size, is

Ir Wilbur De Kruijf, e-mail wilbur@medspray.nl, phone +31 (0) 53 7112835.

being tested with various liquids to see how it is affected by viscosity.

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Image: Philip Broos

Macroscopic image of an innovative microbial culture carrier produced by MicroDish. The twin-layer chip has a porous lower layer and a upper layer with hundreds of etched wells (each measuring 180 micrometres across). This has turned out to be an ideal substrate for use in a computerised microscope system that checks TBC bacteria cultures for minute changes in growth. The faster the changes can be detected, the faster TBC can be diagnosed.

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Slow grower hunted down at high speed

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Micro-imaging of tuberculosis bacteria: recent progress

Tuberculosis is once again an emerging infectious disease all over the world. Better, and especially faster, detection methods are urgently needed. Microbiologists, biotechnologists and engineers have joined forces to develop a fast and reliable laboratory test. Using computerised digital microscopy, large numbers of microbial colonies grown on a very porous substrate can soon be analysed by chip at high speed. By Marion de Boo susceptible to galloping consumption (as is used to be called), so the combination is disastrous. To compound matters, the spread of multi-resistant tuberculosis is becoming a growing threat to public health in large parts of the world. Worldwide, half a million cases of multi-drug-resistant tuberculosis are an added burden. Particularly in the former Eastern bloc countries, inadequate treatment, with patients failing to complete their antibiotics course for example, encourages the selection of resistant strains. Tourism and other international contacts mean that this epidemic may eventually affect public health in the Netherlands too. Speed vs culture Together with two partners, the Royal Tropical Institute (Koninklijk Instituut voor de Tropen, KIT) is now looking for a faster detection method for tuberculosis. KIT, which celebrates its first centenary this year, is a knowledge centre for culture and sustainable development. It has its own biomedical research department in the Academic Medical Centre (AMC) in Amsterdam. “TBC diagnostics are based on two different principles, a direct test or a culture”, says KIT’s project leader Dr Richard Anthony. “The traditional TBC test consists of smear microscopy, with lung mucus being smeared onto a slide and then stained. It is a quick test, but its sensitivity is low and it takes a lot of time to check all the slides under a microscope. Also, the tests are able to detect bacteria in the lung mucus of no more than 60 to 70 percent of the patients.”

(Image: www.MicroDish.nl)

Every second, someone somewhere in the world becomes infected with the tuberculosis bacillus. Contrary to popular belief, tuberculosis is a rapidly growing health problem on a worldwide scale. According to the World Health Organisation, the number of chronic cases in 2007 was estimated to be 13.7 million, with another 9.3 million new cases and 1.8 million deaths, mostly in developing countries where over 98 percent of all new cases of tuberculosis occur. Together with AIDS and malaria, tuberculosis is known as one of the three diseases of the poor. In the Netherlands, about 1000 new TBC cases occur every year. Half of these patients have open lung tuberculosis and are therefore a source of contagion for others. In the first half of the twentieth century, the annual number of TBC-related deaths in the Netherlands was as high as 7,500, but nowadays practically every Dutch patient can expect to make a full recovery. Elsewhere in the world the outlook is not nearly as rosy for the disease kills if left untreated. In many African and Asian countries about 80 percent of the population is infected with the TBC bacterium – even though the disease itself can often take many years to show symptoms. In the United States 5 to 10 percent of the population has been tested positive. In many areas where TBC occurs, HIV is also a common co-infection, in particular in southern Africa. The combination is very dangerous because the immune system of HIV patients is already weakened, offering less resistance to the TBC infection. The disease is also more difficult to diagnose in such patients. People with an HIV infection are particularly

SEM image of TBC bacteria growing on a culture chip with a special support of porous aluminium oxide with cells measuring 3 to 5 micro­ metres across. The culture chip was developed by Micro-Dish B.V.

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(Image: KNCV archive, www.tuberculosis .nl)

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Dutch tuberculosis patient of the 1930s. Even in the Netherlands (Image: KNCV archive)

tuberculosis remained a high-incidence disease for a long time, claiming about 7,500 lives every year. The Nederlandsche Centrale Vereeniging, (NCV) was established in the Netherlands to fight the disease in 1903.The NCV became the KNCV in 1953 and later merged with the Dutch tuberculosis fund Nederlands Tuberculose Fonds, to

In 1950 the rural populace was served by a mobile TBC check up clinic.

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The special TBC test room of the Sophie Foundation, circa 1930.

(Image: KNCV archive / Photo Kunst – H. van der Meulen, The Hague)

become active in 46 countries from the 1970s onwards.

Slow, insensitive, and dangerous Culture-based tests are much more sensitive, according to Anthony. “However, the drawback is that it takes several weeks to get a result from them. Tuberculosis bacteria are very slow growers by nature. Whereas the well-known E. coli bacteria can have a replication time of 20 minutes, tuberculosis bacteria take about 20 hours to divide. The traditional, century-old laboratory culture method, which uses coughed-up lung mucus, can take three to six weeks. On top of that these tuberculosis culture methods are labour-intensive as well as dangerous.” Tuberculosis is a class III microorganism, which means that researchers can only grow cultures in certified laboratories with air flow designed to minimize contamination and other special safety precautions. This makes culture testing complicated and expensive. Anthony: “The fact is that in spite of all the associated problems, many researchers still prefer bacteria cultures, because they offer more options for additional epidemiological research. The advantage of culture testing is that – unlike smear microscopy – it also allows the sensitivity to antibiotics to be determined. That is why KIT is working on a faster version of the culture test, but by definition it will never be a really rapid test. Alternative, faster culture tests exist that use liquid media, but they are complicated or very labour-intensive, which explains the push to improve the classic culture techniques.” Another advantage of a more sensitive test is that it will help to minimise the volume of dangerous tuberculosis bacteria that need to be grown. The new test method detects very small microcolonies, invisible to the naked eye. Biological safety is a major point in favour of micro-imaging. In other MicroNed projects KIT is helping to develop molecular test methods, which are based on protein detection, or RNA or DNA hybridisation, for example. Molecular methods lend themselves well to finding answers to very specific questions such as, is a certain antigen present on the surface of the microorganism, or isn’t it? On the other hand, molecular methods are not very good at telling living and dead microorganisms apart, or fast and slow-growing ones, and these happen to be important questions when tuberculosis is involved.


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In 1962 children in Zaandam (a town in the Amsterdam vicinity) are given a tuberculin jab (the Mantoux test) at Nurse Visser’s clinic.

(Image: KNCV archive / Photopersbureau Schiedam)

A picture a day KIT is now using the digital microscope as a bright field, or light, microscope, but it can also be used as a fluorescence microscope. “I’ve programmed the microscope to automatically take a picture once a day to see if the colonies have grown”, Den Hertog explains. “You can adjust the X-Y table so that the camera always looks at exactly the same positions, so the X and Y coordinates are determined. This enables us to follow the behaviour of each individual microcolony with great accuracy, both the normal

(Image: KNCV archive)

Computers are always vigilant One of the problems with direct manual assessment of smear microscopy is that it takes so much time, as a result of which the lab technicians who have to look at them all day tend to get bored and become less alert. Another problem with conventional methods is that in some case the lung mucus of a patient contains too few bacteria to produce an unequivocal result. If the number of bacteria in a millilitre of mucus is less than 10,000, you won’t be able to spot them on the microscope slide. So, as part of a MicroNed project, KIT developed an alternative, fast culture method, in which the bacteria are first grown into small microcolonies. Although this takes slightly more time than the direct smear microscopy method does, it makes the test much more sensitive. “Detection has now become possible at a very early stage”, says medical biologist and post-doc researcher Dr Alice den Hertog of KIT. In addition, computers always remain alert. The researchers use an advanced special computerised microscope, developed by the company CCM in Nuenen, in combination with a very porous substrate with interesting properties on to which the tuberculosis bacteria are grown into microcolonies. The growth of each individual microcolony of bacteria is assessed by means of computerised microscopy. Anthony: “This special microscope has been fitted with a camera that takes pictures of the growing colonies of bacteria, and these are then analysed very accurately by a computer. Although computers still aren’t very good at identifying individual objects, they are very effective at detecting small changes in images over time.” Den Hertog slides a carrier holding four samples under the microscope. “Look, you cannot even see the microcolonies with the naked eye, but the microscope can.”

(Image: KNCV archive / Huizinga Photo, Rotterdam)

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One of two ways to diagnose tuberculosis in a patient is by means of an X-ray image of the lungs, as shown here, sometime during the 1940s. The other way is by studying a smear of sputum through a microscope.

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growth and the response to different antibiotics. Another useful feature is that the microscope knows what to focus on in every point it looks at.” One of the advantages of the special substrate, a porous aluminium oxide membrane, is that it can be used in combination with various liquid and solid media. Also, the porous substrate can be used to transfer the microcolonies to a new medium, a selective antibiotic for example, without disrupting their growth process. This makes it possible to quickly test the microcolony cultures for resistance to drugs. Anthony: “Since we are monitoring their growth very closely, we can notice very quickly how the microcolonies respond to changes in the nutrient medium. This helps us to better classify strains, and enables us to track down the resistant bacteria, for example. When bacteria have infected a person, it is very important to find out to which antibiotics they are resistant, even more so because some antibiotics are much more dangerous to the patient than others.”

(Image: KNCV archive)

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1960s.

(Image: Ilse Blijker / KNCV)

An assistant studies a sputum smear in the open field in Africa in the

Administering and reading a Mantoux test is a job that demands

(Image: Ilse Blijker / KNCV)

accuracy and requires good training.

A Mantoux test being administered in Kenya by a member of the Koninklijke Nederlandse Centrale Vereniging, KNCV for the prevention of tuberculosis.

Interior view of the prototype μScan microscope produced by CCM. This unit was used to demonstrate the technical feasibility of detecting bacteria on a microsieve.

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As the number of antibiotics-resistant strains of tuberculosis bacteria grows, the need for fast, cheap, automated test methods for direct susceptibility testing increases. The method can also be used for research purposes, for example to test new drugs quickly in detail. The aluminium oxide substrate on which the colonies grow, forms a very porous membrane (Anapore™), which is placed on a nutrient medium of agar. The bacteria can easily reach the nutrients through the membrane. The bacteria themselves have been grown in a liquid which is diluted to a concentration of a few hundred bacteria per microlitre. For each sample, a pipette is used to deposit a solution containing approximately 500 bacteria onto the substrate. “From this, 500 microcolonies could grow”, Den Hertog explains. “The method produces the best results. You don’t want the agar to become completely overgrown with a dense mass of bacteria, but neither do you want there to be so few that they hardly show up in the pictures.” No air bubbles The analysis of the recorded images is done by means of special image-processing software, partly based on open source code. KIT has also developed its own tools for accurate comparison of


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Creative solutions The computerised digital microscope that recently entered service at KIT was built by CCM, Centre for Concepts in Mechatronics, based in the town of Nuenen near Eindhoven. The private research and development company was established in 1969 by Professor Alexandre Horowitz (of Eindhoven University of Technology) and now has about 100 employees building

(Image: J.H.W. Spitshuis, CCM)

the pictures. The main advantage of using a computer is that the analysis can now be focused on growing objects, in other words, the expanding colonies. The colonies start to become visible when they measure about 50 to 100 pixels across in the picture. If only a single picture were taken, the budding microcolonies would not be easy to recognise among all the specks of dust, air bubbles in the agar, and other irregularities on the grid, all of which are about the same size. A series of time-lapse pictures on the other hand, always taken from the same position, makes it much easier to spot the colonies. Specks of dust and air bubbles don’t grow and can thus be automatically eliminated from the analysis, greatly simplifying the process. Den Hertog: “We have tested this concept and demonstrated that it can be used to distinguish between growing colonies and colonies that don’t expand, and it also enables us to judge the growth rate. It could be a solution for tuberculosis, but the system could also be used for other types of analysis. Water and soil samples, for example, sometimes contain a cocktail of fast-growing and slower species. The current practice is usually to ignore the latter, but this new technique could be used to make the slow-growing strains visible too.” This will require additional effort on the software front. The robustness of the inoculation also needs to be proven, and it remains to be seen whether different types of colony in a mixed solution can really be identified. The ultimate objective of the KIT project is to have a fast culture method suitable for use in developing countries. “That’s certainly going to take another ten years though”, says Anthony. “People have been working on a dipstick for 40 years, but there is still a lot of junk on the market in that field. The usual immunological tests are often not very specific. A test will probably always need to include a bacterial culture. And that means involving one of the better equipped, central laboratories.”

Close-up view of the microsieve in the sample carrier of CCM’s μScan

illuminated with blue excitation light. The fluorescent light returned by

microscope. The original idea was to filter the sputum of TBC patients

the sample is much weaker and invisible in this picture. To ensure that

through this microsieve, but the properties of the sputum turned out to

the returned light can be recorded by the camera, an emission filter

be too varied among patients. The image shows the microsieve being

blocks the blue light so only the fluorescent light will pass.

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machines and equipment for a wide range of customers. “From picking robots for mushroom growers to space exploration instruments – we’re always looking for creative solutions”, says project leader Dr Ir Frank Fey. “Computerised image-processing of microorganisms could cut laboratory costs by a big margin”, says Fey’s colleague, Ir Edwin Langerak. “Now that the technology is coming of age, we can see all kinds of applications, not just for body fluids, but also in such fields as water and food monitoring. The challenge as always is to ensure that the quality of the analysis keeps improving. Improved preprocessing will also enable us to keep lowering the detection limit. In theory CCM can track down a single bacterium in a litre of water, if only it doesn’t decide to stick to the rim of the glass.” The idea for digital microscopy arose from an earlier project that CCM started together with KIT about five years ago.

KIT’s Dr Alice den Hertog uses the μScan microscope to scan microcolonies of mycobacteria for growth.

Display of the μScan microscope showing how the

The μScan scanning a culture field containing colonies of

instrument starts by measuring the distance from

mycobacteria. The device can be set to take a series of pictures of a

the sample in three different places before scanning

selected number of fields at the same time each day. By comparing

the image, in order to maximise the depth of field

successive images of the same fields, the progressive growth can be

across the entire sample.

assessed.

µScan proces description

Read recipe Find focuspoints

Focus points

Calculate image plane

Bovenschrift: μScan process steps X,y,z image plane

Step toimage position Scan images (multicolour)

The surface of the microsieve and the MicroDish culture carrier are digitised by means of a step & scan

Continue next position

process. The images are then automatically analysed for the presence of bacteria.

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Images

Process images

Analysis

Generate overall report

Filtering lung mucus Fey: “The original plan was to filter the lung mucus from TBC patients using microsieves. The idea was to first stain the bacteria on the sieve and then use a microscope to analyse them, all within fifteen minutes. Compared with the time of several weeks for a result from a culture test, the idea was nothing short of revolutionary! We thought that if we could make it work for difficult, slow-growing TBC bacteria, it would also work for easier applications. That’s why we wanted to developed microfiltration as a platform technology.” Unfortunately the first project failed because the lung mucus, viscous like chewing gum, turned out to be difficult to process through a microsieve with pores barely half a micron across. However, fortunately the growth monitoring can be performed without the filtration step. Autofocus To assess the images, CCM came up with a smart automated analysis technique. The usual procedure is for the microscopist to readjust the focus for each new sample. As any amateur photographer knows, it’s easy to get the horizon in focus, but close-ups of flowers or insects are much trickier. Basically, as the magnification increases, the depth of field decreases. A tuberculosis bacterium is about 0.3 of a micron wide, and about one micron long and high, but the depth of field of the microscope is no more than 1.5 micron. A tricky job indeed.


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“Fortunately a microsieve – which is a microchip with an aluminium oxide membrane – has a very smooth surface”, says Fey. “If you can find three points on that surface, the laws of geometry say that you can draw a plane through those three points. Now if you adjust your focus for those three points and optimise the lighting for the calculated plane, you can scan and sample the other points in that plane very quickly and efficiently.” This approach reduces the time-consuming refocusing operations to a minimum. CCM uses smart, patented mathematical techniques to quickly calculate the plane each time. The angle of each plane also makes it possible to extrapolate fairly accurately which way the microrelief will go and what the angle of the next plane will be.

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Images taken by Dr Alice Den Hertog with the μScan (magnification ×5) clearly showing the growth of the individual microcolonies over a period of ten days.

Illumination The CCM company builds all kinds of microscopes. Each customer has specific requirements. They contain a lighting system and a camera, a motor to move the samples, and a range of fluorescence filters. Fey: “We can also programme in several ‘protocols’, for example, find spots that look like a particular feature, and illuminate them in the desired way. Our microscopes are fully configurable and flexible.” One of these custom-made machines will set you back something like € 40,000. The resolution of black and white images tends to be better, so that is what KIT decided to acquire, but if you want to scan for different kinds of bacteria, images in colour can sometimes be preferable. Fey: “We use a range of different light sources: blue, amber, violet, and ultraviolet. The smart thing about our microscopes is that there is no need to change mechanical filters, which always costs time and causes minute shifts in position. All you have to do in our case is switch on a different light source. Our filter sets are built in, as it were.” A lot of effort has gone into finding the right lamps. The mercury lamp original fitted, which used 150 watts and burned for only 1000 hours, has now been replaced with a practically indestructible LED unit that use only 3 watt, which is a much better option for developing countries. Experiments are continuing to achieve faster, sharper images.

A few years ago when microbiologist Dr Colin Ingham was looking for an alternative to improve the agar culture substrate for TB bacteria in a Petri dish, he discovered a porous aluminium oxide. This material had been created by accident in the 1980s at the ALCAN research lab. μScan microscopes during final assembly. In the foreground the electronics and the microscope casing are visible. The small horizontal cylinders on the side of the instrument are the three narrow-band LED light sources, each with its own wavelength. The light is focused on the sample using dichroic mirrors and excitation filters. Through an emission filter, only the reflected fluorescent light reaches the camera to create the image.

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Image: Philip Broos

“If you take more points, you get a sharper image, but it also takes more time”, says Fey. “Compared with a year ago the image quality has made another spectacular jump forward. The imaging process and the analysis process are now nicely matched, and the next step will be to produce fully automatic reporting and diagnosis.”

Close-up of the MicroDish culture carrier. With pores up to 200

oxide with 120-nm pores. Onto the substrate, a 10 to 40-µm thick

nanometres across, the aluminium oxide caught the attention of

layer of acrylic was laminated into which 180-µm diameter wells

Dr Ingham as a potential substrate for bacteria cultures. The physical

were etched. The aluminium oxide and acrylic sandwich is made as

structure is ideal for growing microorganisms, the pores are big

part of a wafer which is then cut into separate pieces. This type of

enough to let nutrients through, and the material itself is inert.

culture substrate is ideal because it can be moved to another nutrient

Ingham made a design, which in collaboration with Mesa+ was

substrate without disrupting the growth of the bacteria.

transformed within a year into a substrate of 60-µm thick aluminium

Optical microscope image of the growth of bacteria in the circular 180 µm wells. The bacteria have been treated with a stain to make them easier to detect with a fluorescence microscope. The bacteria show up as a colony of white microorganisms, while the wells themselves have

Micro-imaging The CCM microscope at KIT has been fitted with a different sample carrier than the one normally supplied by CCM. Den Hertog uses a sample carrier featuring special chips developed at the innovative company MicroDish, established in 2008 and another MicroNed partner. “We developed a chip that can hold as many as a million cultures”, says microbiologist Dr Colin Ingham. Ingham is Chief Scientific Officer at MicroDish. Much of his research was done at the Top Institute for Food and Nutrition. Wageningen University’s Professor Willem de Vos is scientific consultant to the company, which also works closely with Professor Albert van den Berg of the Mesa+ Institute for Nanotechnology of the University of Twente. Both professors are Spinoza Prize winners. To demonstrate, Ingham slides a chip under a microscope. “This model has minute square compartments or wells measuring 40 × 40 micrometres”, the researcher explains. “The ceramic material used, a very pure kind of aluminium oxide, has a very remarkable structure. Not only is it very porous, it is also very inert and stable. It does not stretch or shrink when you pull it or heat it – which is sometimes necessary to kill the bacteria.”

been given a coating of platinum that makes (Image: MicroDish / www.microdish.com)

them non-fluorescent so they look black. The extremely flat surface of the culture substrate is very useful given the very small depth of field of a microscope.

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Honeycomb The walls between the wells have a chaotic honeycomb structure that allows the nutrients to reach the bacteria almost unhindered. The raw material, aluminium oxide, is cheap, which is a prerequisite for large-scale application in less affluent countries with a high TBC incidence. Ingham: “We have even made chips with wells measuring only seven by seven micrometres. The great thing about these is that a single chip can hold a million samples. A fast test with a slowly


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reproducing organism doesn’t need a lot of space.” The new model with 40 × 40 micrometer wells provides a little more space for the bacteria to develop into larger microcolonies. Ingham: “Each well is surrounded by walls, so it is like a miniature Petri dish. We can make round or square wells, depending on the application. A sterile tool is used to inoculate the wells with samples. To miniaturise a test, all the ancillary tools have to be miniaturised as well. Our company happens to be the current record holder in the miniaturisation stakes. Nobody has managed to develop a more highly miniaturized culture plate to date.”

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EM image of seven wells on the MicroDish culture chip. In the centre a growth of

Microstructure Ingham has experimented a lot with the microstructure and the geometry of the material. “We learned a lot from our experimenting. Nanotechnology and microengineering offers fantastic possibilities. We first tried to fill the chip with a liquid polymer to build the walls of the microwells. We used a kind of glue that hardens only if you shine ultraviolet light on it. The idea was that we would be able to build up the walls around the wells by shining UV light only on the places where the walls were to come, but the result was a disaster. The remainder of the glue remained liquid, but it was impossible to remove it from the wells because of the capillary forces. The entire chip turned into a single closed slab.” A better result was achieved by etching holes in a membrane and laminating them with a substrate of aluminium oxide. Ingham: “We’re still fine-tuning the chip. It needs to have a laminated rim so it can be easily lifted without contaminating the samples, and it needs to have a grid system so you can tell what the exact position of each sample is. In addition each chip will need to be given a barcode to make it suitable for mass processing by computer without creating extra paperwork.”

unknown bacteria can be seen. The well on the left shows another culture. The distance between the wells is large enough to the prevent the different bacteria cultures from merging, so the separate microcolonies remain easily distinguishable.

For more information please contact Dr Anthony Richards, phone +31 (0) 20 5665450, e-mail r.anthony@kit.nl, or Dr Alice den Hertog, phone +31 (0) 20 5665454, e-mail a.d.hertog@kit.nl, or Dr

Streptococcus cells are seen here growing in a single 180-µm

The μScan sample carrier used at KIT has been modified to accept a

Ir Frank Fey, phone +31 (0) 40 263 5000, e-mail frank.fey@ccm.nl, or Dr Colin

well. Hundreds of individual cells can be easily made out in this

conventional sample holder with culture dishes in which MicroDish

Ingham, phone +31 (0) 6 42477078, e-mail c.ingham@microdish.nl.

fluorescence microscope image.

culture chips are used.

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Take a gold bead about 80 nanometres (1 nm = 10-9m) across, attach it to the end of a strand of DNA, and glue the other end of the DNA to a sheet of glass. Add a little water plus the contents of a plant cell, and within a few minutes you can see (using a microscope) whether the cell material came from fresh produce or whether the concentration of a healing substance will rapidly decrease. This is the new technique being jointly developed by the Quantitative Imaging research group at the Faculty of Applied Sciences of the TU Delft and the Food Quality Analysis research group at the Food & Biobased Research department of Wageningen University. The technique can be used to detect the presence of minute quantities of mRNA within minutes, based on the ‘swaying’ of the gold bead stuck at the

The shiitake mushroom (Lentinus edodes) originated in China and Japan, but has since become one of the most frequently grown mushrooms worldwide. It grows on dead wood, and it is a member of the white-rot family of fungi. Shiitake mushrooms thank their popularity in culinary circles to their nice bite and special taste. In addition, many people ascribe healing properties to it.

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(Photo: Philip Broos / Leiden)

end of the strand of DNA. Though other mRNA methods for such measurements do exist, they take longer and can be error-prone. In any case, freshness tests need to be quicker, because a day’s wait (as is currently the standard) is much longer than is needed in practice. By Joost van Kasteren


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Testing freshness with gold-tipped DNA

DNA copy Let’s start with a few biochemical bridges. In cells of plants and animals, substances like Lentinan are formed with the aid of proteins. These proteins in turn are produced by ribosomes, certain regions within the cell, translated from a molecule known as messenger RNA, or mRNA for short. An mRNA molecule is a copy of a piece of DNA and contains the same genetic data, but it contains an extra oxygen atom. To determine whether the highly prized Lentinan is being formed in the mushroom, and remains present from growing bed to retail shelf, it helps to demonstrate the presence of the specific mRNA responsible for the production of the protein that enables the production of Lentinan in the cell, or regulates its disposal. The method can also be used to monitor the presence of other types of mRNA, like those associated with the shelf life of food. The great thing about this fast testing method for mRNA, known as TPM (Tethered Particle Motion), is that the method is quick and relatively sensitive. The test results are also relatively simple to read, because the optical dark field microscope needed to measure the movement of the gold particles with the required precision is comparatively simple and cheap. The underlying principle of the Delft method

String Imagine a balloon filled with helium gas, tied to the balcony rail with a length of string. Clearly the movement of the balloon in the wind will be restricted by the length of the piece of string. Something similar takes place with the TPM technique developed in Delft. You use a protein to stick one end of a piece of DNA (less than one thousandth of a whole strand of DNA) to a substrate, glass for example. At the other end of the DNA strand you use another protein to stick on a minute bead of gold about 80 nanometres (= 0,00008 mm) across, and then you immerse the lot in water (in a microfluidic flow cell). The thermal energy will cause the water molecules to bump into the gold particle, which will start to move from side to side (Brownian motion). The singlestranded DNA (in its natural form a DNA molecule consists of two complementary strands, the famous double helix) has a tendency to coil itself, thus reducing the effective length of the ‘string’ and thereby the freedom of movement of the gold particle. If an mRNA molecule from a plant cell were to come near the fixed DNA strand and ‘dock’ with it because it has the same genetic code, the presence of the mRNA will cause the DNA strand to partially uncoil. As a result the gold particle will be able to swing

The active ingredient in shiitake mushrooms, Lentinan, a compound formed of a large number of sugar molecules, is thought not only to reduce blood cholesterol levels, but also to stimulate the production of T cells, supporting the immune system and possibly

(Image: Philip BRoos / Leiden)

is so simple that you might be forgiven for thinking anyone could have come up with, but this is belied by the fact that the Delft research group is the first in the world to use the method to test for a single molecule of mRNA. Proper lab hygiene is of course a must when using the method, for the microfluidic flowcell is easily contaminated with a few molecules of the ‘RNA-eating’ enzyme RNase, which is found on our skin and hairs. That is not to say though that the test requires cleanroom conditions, says Ir Sanneke Brinkers who, together with her colleague Dr Heidi Dietrich, is working on the project at the Quantitative Imaging group of the faculty of Applied Sciences at TU Delft. “As long as you use gloves, keep your workbench clean, and don’t scratch your face, the risk of contamination is not that big.”

providing a solution against cancer. Culinary shiitake merchants would like to be able to tell the freshness of mushrooms offered for sale, while growers supplying shiitake for medicinal use would like to be able to time their harvests to coincide with maximum Lentinan levels. A MicroNed project brings together researchers at TU Delft and Wageningen University to work on a method that can quickly supply both pieces of information. The method is based on detecting mRNA using an optical microscope.

(photo: Food & Biobased Research van Wageningen UR)

It looks like a simple mushroom, although its cap is a bit flatter. The shiitake, or to give it its proper name, Lentinus edodes, is one of the most commonly grown mushroom in the world. It is native to East Asia, being grown in countries like China and Japan, and in particular in the colder, higher regions. The shiitake is a mushroom that grows on dead wood, and is a member of the white rot family of fungi. In the Far East it is reputed to have medicinal properties, lowering the blood cholesterol level, curing hangovers, and generally improving the body’s resistance to disease. Most of all, it is believed to help stave off cancer, thanks to its Lentinan content. Lentinan is a compound made up of a large number of sugar molecules, and is said to improve the ability of our immune system to clear tumor cells from the human body.

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The detection of mRNA can also be used to predict the shelf life of vegetables and fruit, for example by predicting at an early stage which batches could be prone to storage problems such as brown core development in pears.

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(Image courtesy of Jane Wang, The Science Creative Quarterly)

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The ripening process in fruit and the production of a substance like

CYTOPLASM Nucleus Free amino acids

Gene

many other processes in living tissues). The genetic information stored

tRNA bringing amino acid to ribosome

proteins. The information is transferred by a messenger molecule (mRNA = messenger RNA) to the ribosome, a part of the cell that produces the required proteins based on the building code it receives.

mRNA

Ribosome incorporating amino acids into the growing protein chain

Sanneke Brinkers sticks two microscope slides together with double-sided adhesive tape to

mRNA being translated

Ribosome

make a microfluidic flow cell. A pipette is then used to inject the

The DNA in a cell nucleus consists

liquid containing the DNA strands

of a double-stranded helix. The

between the slides. One end of

code in each of the strands

each strand will attach itself to the

complements the code in the

lower slide. Then a liquid is injected

Base Pair

C

A

Adenine

G

T

G

Sugar Phosphate Backbone

G

T A

Cytosine Thymine

G

T G

A

G

A

C

C

T G

A G

T

C

A

C

Guanine

other. The building blocks of DNA

G

C

Nitrogeous are the nucleotides, which consist Base of a sugar phosphate group and a

containing gold particles that attach themselves to the free end of the DNA strand. The microfluidic flow cell is screwed into a carrier and studied under the dark field microscope.

base (adenine, cytosine, thymine,

Oligo Of course you don’t have to actually sit peering endlessly through a microscope, Brinkers explains. You can record the images using a special camera, and then later use image processing software on a computer to track the movement of the gold particle and measure its swing to see whether an mRNA molecule has ‘docked’ with its complementary section on the strand of DNA. For the image processing part, Brinkers and her co-researchers used the graphical processing unit (GPU) of the computer rather than the central processing unit (CPU), as is usually the case. The great thing about a GPU is that it can carry out many operations simultaneously, which greatly reduces the time consumed by image processing. GPUs have always offered this capability, but it wasn’t until electronics manufacturers recently made the Compute Unified Device Architecture (CUDA) available to scientific imageprocessing researchers developing their own graphics software, that they could access the GPU directly.

or guanine). Adenine is always located opposite thymine, and cytosine always faces guanine. The mRNA molecule

C

is similar, but instead of thymine it has a uracil base and it has an added oxygen atom. Generally, mRNA is single stranded.

The temperature of the carrier can be controlled and maintained to within one degree. This is required for the temperature dependent hybridisation kinetics between mRNA the complementary DNA strand. The tubes on either side are the feed and drain connections. The movement of the gold particles in the microfluidic flow cell is studied using a dark field microscope, generally with a magnification of 100 times. A special CCD camera on the other side of the microscope is used to record 200 images per second for dynamics studies; for the mRNA tests the rate is only 2 images per second.

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wider. All you have to do is peer through a microscope to see whether the mRNA molecule is present: if the gold fleck starts to swing wider, bingo!

in the DNA inside the cell nucleus contains the building code for these

mRNA copying DNA in nucleus

DNA

Lentinan in shiitake mushrooms are regulated by proteins (just like

So how can you tell that the uncoiling of the single-stranded DNA isn’t caused by something else? Brinkers explains how the team used RNA purchased from a specialist supplier to demonstrate the operating principle of the measuring system. She won’t be drawn out, though: “We still have to be a bit careful. Heidi recently completed the first series of tests, which enabled us to see that the mRNA attaches to the DNA. This demonstrates the validity of the operating principle of the system. We didn’t just do the tests using RNA, but also with certain other molecules known in biology as oligos.” Oligos (oligonucleotides) are minute pieces of genetic material. Brinkers shows a few images: “If you look at this image (see diagram Excursion page 35; eds), you will notice that it takes some time before the swing increases, about fifteen minutes. This is because it takes some time before an mRNA molecule comes close to the DNA strand. The uncoiling of the strand also takes a while. This is because the mRNA does not attach itself to the DNA strand along its entire length in one go, therefore it takes a while for the linking process to complete. So far, we have been


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able to demonstrate that this technique can be used to prove the presence of certain mRNA molecules. It means that the operating principle of the method is sound. Now we still have to find out how specific the method is.” Blinking quantum dots Product freshness is of course a popular theme at Wageningen University, which started life as an agricultural college. Researchers had been looking for a method that would be cheaper and faster than the available techniques, and so they decided to participate in this MicroNed project. In potency, the new method could also be used to measure the concentrations of several mRNA molecules by using several complementary DNA strands simultaneously. Brinkers: “It is not as simple as it sounds, but we’re working on it.” As far as they know, the Delft researchers are the first in the world to use the system of gold particles and a dark field microscope. Some have been using a TIRF (Total Internal Reflection Fluorescence) microscope, while other have been using polystyrene or latex beads, but these are at least two and a half times as big as the gold ones. Brinkers: “You want to be able to detect the motion, but the particles mustn’t dominate. The gold particles are small, but we can go much smaller still. One option might be to use blinking quantum dots. These dots, that follow the laws of quantum mechanics, could also be attached halfway along the DNA strand to enable us to see what’s going on there. We’re also planning to have a kind of loop or hairpin built into the DNA strand, so when the mRNA molecule docks with the DNA strand , the loop will open to extend the strand’s length in one fell swoop, which would provide an even better and clearer indication of the presence of the mRNA you’re looking for. We won’t be doing that ourselves, of course. We deal with the physics.”

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An mRNA-meter Through microfilters the extract of a plant cell’s contents is added to a micro fluidic flow cell, to the bottom of which gold-flecked DNA has already been attached. It is then placed under a microscope. The researchers at Delft University of Technology use a dark field microscope, which uses scattered light, because it yields high-contrast images. Unlike in fluorescence microscopy (a method often found in biology laboratories) the flecks of gold do not carry the risk of ‘bleaching’, gradually extinguishing their fluorescence. The changes in the way the gold moves indicate to what extent the piece of DNA is extended as an mRNA molecule attaches itself. Basically this is a single molecule system, but the

substrate could hold several pieces of DNA. To simultaneously follow multiple reactions involving the specific mRNA, all a researcher has to do is to attach strands of different types of DNA. This mRNA meter can be used for purposes other than just determining the level of freshness of food. In principle it could be used to visualise a whole range of synthesis, regulation, and decomposition processes in a cell, which could be used to optimise many different products. It can also be used to measure the concentration of some substances that are being synthesised inside a cell with the aid of certain proteins, or to record a cell’s protein spectrum. The range of applications is limited only by our imagination.

Three-dimensional Brinkers: “We also want to add the third dimension to the observation. The mRNA molecules from different genes dock with our DNA strand in different ways. Conceivably, one type of mRNA molecule would fit the DNA exactly and therefore dock with all the adjacent nucleotides (the building blocks of DNA and RNA), 33


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Principle of the dark field microscope. Unlike a normal optical microscope, in a dark field microscope the illumination path is separated from the imaging path. The light strikes the object at such a large angle that the reflected light can no longer enter the imaging path. The CCD camera captures only the light scattered by the gold particles.

This image, as seen through the eyepiece of Brinkers’ microscope, results from the incident light coming in from the side causing the orange gold particles in the foreground to light up brightly against the dark background. Where there are no gold particles to disperse the light, it remains dark, which is why the instrument is known as a dark field microscope. A scale model (100.000:1) makes it easy to see how the water molecules (simulated by blue styrofoam granules) are constantly moving about as a result of thermal energy. As they collide with other molecules, they also cause the gold particles to move about (i.e. the gold particles are undergoing a Brownian motion). They are attached

In each image of the CCD recordings, the position of the

to DNA strands, which affect the movements of the particles and keep

particle is measured. If all the positions of a single particle

them within a certain area. The distribution of their positions depends

are superimposed in a single image, together they represent

on the flexibility and the length of the DNA strand.

the position distribution of the gold particle.

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whereas a different mRNA molecule would skip a few nucleotides, creating an extra loop in the DNA strand. The added loop would then cause the swing of that DNA strand to be reduced, so the gold particle will reach less high. This would provide additional information from that third dimension, the height. We would also like to use the height to be able to distinguish between a small swing caused by the DNA being coiled and a small swing because the gold has stuck to the glass. If the gold gets stuck, it will probably not be in the same place as the point where the DNA is attached to the glass. We have already been able to get this information from earlier measurements. If the DNA strand is coiled, however, it will be close to the point of attachment on the glass. Another example of using the third dimension is when you want to detect proteins instead of mRNA molecules. Some proteins will attach to the entire DNA strand and so stiffen it, restricting its movements. These proteins can also stick to the glass, but by measuring the height we can see whether this happens or not. There are no formulas yet to calculate the exact movement of the particles, and this is true in general. I have made a simulation that showed us that the height adds much more information.” Brinkers has found that you can also determine the height of the particles with sufficient precision: “If you image the bead just off the focal plane, the sharpness, or lack of it, of a gold particle will enable you to reconstruct the image in the third dimension.” Principle For the time being, at least a few years, the project group will be occupied with working out a whole range of details. So far the research has demonstrated that the principle of the mRNA meter is sound. Dr Jurriaan Mes of WUR: “We support the research by providing various DNA fragment and RNA samples. In the meantime we will keep looking for the indicator genes. You need them to verify your quality measurements and to predict the development of healthy ingredients. As long as the new method hasn’t yet been fully developed, we will use the Real Time PCR method. As soon as a faster method becomes available, we will use the indicator genes to make the method ready for practical use, and specifically for the various demands growers and traders are making of their products.” Apart from the Quantitative Imaging group of TU Delft (handling the physics and materials side) and the Food Quality Analysis


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research group of Wageningen University (which synthesises the pieces of DNA), other parties involved in this MicroNed project are the Friesland Food and Aquamarijn companies (microfilters). The Aerodynamics and Hydrodynamics Laboratory of TU Delft and the Biophysical Engineering group of University of Twente are also involved in the mRNA measuring project.

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One of the concepts Brinkers and her fellow researchers intend to try out is a further shortening of the singlestranded DNA by looping it. By selecting the right DNA coding, it should be possible to make the strand attach to itself at a certain point. The mRNA molecule has a much greater affinity for attaching itself to the DNA, and as a result the loop will open. This will significantly

For more information please contact:

increase the swing of the DNA strand and with it the

Ir Sanneke Brinkers, phone +31 15 2783221, e-mail s.brinkers@tudelft.nl, or

excursion of the gold particle. This would make it even

Dr Jurriaan Mes, phone +31 317 481174, e-mail jurriaan.mes@wur.nl.

simpler to detect the mRNA molecule.

The extent of the movement can also be described by the

gene A

excursion, i.e. the distance

gene B

control

of the mapping (the 2-D

The method invented by the Delft researchers can also be used to

projection) of the particle

detect multiple genes on a single chip (multiplexing). For this purpose,

relative to the (estimated)

different areas are created onto which different types of DNA strands

A fundamental understanding of the method requires that we are

attachment point of the

and their particles are attached. By monitoring the movements of

also able to measure the vertical level of the gold particle, according

DNA strand. In this case it is

all these particles, the presence of several mRNA molecules can be

to Sanneke Brinkers. The 3D image (right) provides a much better

197 nanometres.

detected simultaneously, which could be used for example to measure

spatial impression of the actual position of the gold particles than the

both the freshness and the ripeness of produce.

2D projection (left) does. This is why she is now actively gathering the level component to be included in the presentation of the measuring

Excursion [mm]

150

Complementary RNA injection

results.

100

50

0

500

1000

1500

Time [s]

2000

2500

3000

Link detected!

Brinkers can determine the level information in retrospect by

If the excursion of the gold particle is followed over time, a small movement can

examining the images produced by the CCD camera. In an image

be seen at the start. This movement is typical for a single-stranded DNA molecule

showing several particles of gold at different levels, only the particles

attached to a gold particle. About 1000 seconds after adding an mRNA molecule that

in the focal plane will be in focus. Any particles above or below the

fits onto the DNA strand, the movement of the particle will increase, until finally it

focal plane will produce different unsharp images. Brinkers has

reaches a level that is characteristic of double-stranded DNA. This means that in the

mapped these differences and is now using them to automatically

intervening time the mRNA has lowly attached its entire length to the DNA.

determine the level component.

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SEM-image of a microcapsule with a wall made of a Bovine Serum Albumine (BSA) pectin-composite. Probiotic bacteria in special drinks and in bean size capsules have become common food supplements which nowadays are for sale in most supermarkets. The period between the production and the consumption is on average two years. The probiotic bacteria need protection against the varying conditions of humidity during storage, transport, shipping, storage at the wholesalers, at the retailers and in the refrigerator in the consumer’s home. The majority of the bacteria in these drinks don’t survive the acid environment of the stomach. To compensate for the loss the dose of probiotics maybe a thousand fold of the quantity required in the intestines, which makes these drinks and capsules expensive. Encapsulating the probiotic bateria in a smart way, by using composite materials, could address all of the above problems and guarantee a programmed release of the active

(Image: Mrs.Yulm Arsiante, Wageningen University)

substances in the intestinal area.

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The taming of the fibril

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Fibrils are fibre-like pieces of protein, once believed to be a future replacement of meat. Fibrils are more than just meat substitutes though, and at Wageningen University food technologist Professor Erik van der Linden heads a group investigating, among others, the possible use of fibrils as membrane materials to protect probiotic bacteria from the moment of production, storage, transport and all the way through to their operational destination within the intestinal tract. This includes protecting the bacteria from a humid environment during the period before consumption, but ensuring the safe passage through the acid environment of the stomach and their strategic release in the intestines. In some cases encapsulating can also prevent the early release of flavours like fish oil. The FrieslandCampina dairy company is an industrial partner in this MicroNed research project. The probiotics capsules haven’t arrived yet, but the fibrils have been tamed, and a solid scientific base has been established. By Arno Schrauwers It all started about thirteen years ago when Erik van der Linden took up his professorship in Physics of Food at Wageningen University. One of the questions he had to answer was how to make a gel with the absolute minimum of material. Fibrils turned out to be eminently suitable for the purpose. Fibrils are fibrelike pieces of protein that are formed when certain proteins (globulins, to be precise) are heated in an acid environment. This causes the proteins to break in certain spots, producing long, rodshaped molecules (peptides) that combine into fibrils that can be several micrometres long (1 micrometre or µm is one thousandth of a millimetre) and only a few nanometres thick (a nanometre is one thousandth of a µm). At the time several of Van der Linden’s students had gained their doctorates for research on the subject of fibrils.

Whey Four years ago, when Cynthia Akkermans started on her doctoral research, her interest was on the use of fibrils to produce, among others, a substitute for meat. She conducted her research in collaboration with the Food Process Engineering group. Akkermans had to start by finding out more about the way an induced flow in a solution of proteins affects the forming of fibrils. ß-lactoglobulin was used as sample protein, one that is found in whey (a by-product of cheese making). The research by Akkermans and seven other doctoral students forms part of a MicroNed programme aimed at producing capsules to deliver probiotics. At least, that is the simple interpretation of the proposed task. In scientific terms the purpose of the research programme was to investigate the assembly and phase behaviour of biopolymers in two and three dimensions, in flow conditions and in a micro environment.

(Image: Jerome Pâques, Wageningen University)

Encapsulating probiotics and drugs for maintaining integrity, safe keeping and programmed release

Food enters mouth

Function: food breakup, carbohydrate digestion pH 6.5 - 7.5

Salivary Glands

Mouth

Food enters stomach

after < 1 minute Function: protein digestion, carbohydrate digestion, inactivation of microorganisms pH 1.0 - 3.5

Esophagus

Liver

Food enters small intestine

after ~ 4 hours Function: fat digestion, protein digestion, carbohydrate digestion, absorption of nutrients pH 7 - 8

Stomach

Galbladder

Small Intestine Duodenum

Pancreas

Food enters large intestine

after ~ 16 hours Function: fermentation of non digestible matter by bacteria, reabsorption of water, ions and vitamins pH 5.5 - 7.0

Food leaves body

after ~ 24 hours

Jejunum

Colon

Ileum Rectum Targeted release Microcapsule

Anus

Probiotics

On their journey from the mouth to its intended destination in the intestinal track, probiotic bacteria pass environments with varying degrees of acidity and mechanical stresses. Each of these conditions requires a different approach to the design of the packaging of these bacteria.

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Image: Cok Francken

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Encapsulation of probiotics (emulsion)

Spray-drying of emulsion into a powder

Spray-dried powder with other dry ingredients

Storage/transport

Transport to wholesale (and storage)

Storage at retail

Purchase by consumer

Storage at consumer

Consumption by consumer

The life of probiotic bacteria: from spray-drying nozzle to intestine

Two year survival FrieslandCampina’s encapsulate needs to survive more than mechanical stress during eating and stomach acids. In fact the journey of the small probiotic capsule through the body is only the final stage of a long trip. The probiotics have to stay alive during the entire production process, logistic chain and consumer handling, right up to their actual consumption and that can easily take two years. The process rather depends on the product you are using the capsules for, according to Marcel Pâques, principal scientist of FrieslandCampina Research. “We looked at the entire chain from product to delivery of the probiotics in the intestine to find out exactly what specifications the encapsulate has to meet to ensure that the probiotic bacteria end up where they are intended, in the intestine. We decided to analyse the chain of a particular product, infant formula, because there are great differences in the required functional properties depending on the application. We mapped out all the conditions the probiotics have to survive”, the scientist explained. “We are talking about the encapsulation itself, spray-drying, transport to the manufacturer of the baby food who mixes the encapsulate with other ingredients, the packaging, transport to the wholesalers, storage in a warehouse, transport to the shop and from there to storage at the consumer’s home. The last step is dissolving of the powder into a drinkable product and finally consumption itself.”

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FrieslandCampina researchers found out that probiotic bacteria have the best chance of survival if humidity is kept very low and stable. Pâques: “The metabolism of the micro-organisms then goes into a kind of hibernation.” Humidity is anathema if you want to keep the bacteria asleep (and vital). The conditions during the entire process are highly delicate. The application of probiotic capsules in infant formula is a first potential product application for FrieslandCampina, but more applications are considered. “Baby food is indeed the most concrete application but as I have already said, you cannot automatically use the developed technology tailored for Infant Formula for other products. Other products applications have a different set of conditions and require different specifications for the capsules. So there’s no question of one capsule fits all. Each application sets its own criteria. We already have yoghurtlike products, but cheese could also be an option.” In fact when Professor Erik van der Linden and his PhD students have finished with their part of the project, FrieslandCampina has to bridge the gap from academia to an industrial application. This crucial step for success is not the easiest part.

Survival through mouth and stomach

Release just in time in the intestinal tract


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Probiotics

(Image: Nagesh Wagdare, Wageningen University)

Although probiotics are sometimes ridiculed, according to Dutch research in 2009 these ‘bacterial drinks’ actually have a positive effect on our health. Our intestinal tract is home to large numbers of bacteria which, among other tasks, help us to digest our food. Inside our intestines the bacteria from probiotics can be useful, but the research – which was carried out by a collaboration of NIZO, Maastricht University, Wageningen University, and the Food & Nutrition institute, has provided some evidence that probiotics could have a positive effect on our immune system. To make sure the bacteria in probiotics arrive at their destination in good health, the product could be contained in capsules that will not release their contents until they arrive in the intestines.

SEM image of a microcapsule prepared by solvent extraction induced phase separation. This method enables the production of a capsule Close-up of the intestinal wall, the area where probiotic bacteria

with a tunable number of minute holes, thus creating an excellent

should finally be absorbed. The probiotics should be released timely

opportunity to regulate the capsule’s permeability.

from their capsule at this area of the intestine, otherwise the bacteria

SEM image of an ensemble of capsules, each consisting of 10 consecutive layers composed of protein based micron sized fibrils and pectin.

There are numerous types of capsules, with different compositions of the interior and the shell. The microcapsule in this confocal microscope image is an encapsulated oil core in a Eudragit rich shell, with a diameter of 25 μm. The oil is stained with hydrophobic Nile Red and the Eudragit with green fluorescent protein (GFP). The oil is mainly present in the centre of the microcapsule, while the Eudragit forms a

(Image: Francisco Rossier, Wageningen University)

Sugar, fats, and proteins This relatively complex research assignment has many aspects. What kind of material should a capsule be made of? How do you make such a capsule, and how do you measure the results of all your efforts? A number of researchers took on the task of investigating these aspects. The choice of material for the capsules is dictated by the requisite functionality and parameters. There are three kinds of biopolymers: (poly)sugars, fats (lipids), and proteins. (Poly)sugars are out because, as Van der Linden puts it, because they are simply too porous for the intended purpose. Lipids ought to be suitable (a cell membrane consists of a double layer of lipids), but according to Van der Linden they offer less scientific scope because much research has already been done in that field, and is still being done. After all, Wageningen University is a scientific establishment. As it is, this is not the only reason

(Image: Nagesh Wagdare, Wageningen University)

Van der Linden: “We’re talking about a stable system that can be used to deliver certain materials, in this case probiotics, to the right place in the body. For probiotics, the right place is in the intestines. It would require capsules smaller than 50 µm, that are mechanically stable, that break down in a controlled manner, that are partially porous, and last but not least, can be ingested.”

(Image: Francisco Rossier, Wageningen University)

face excretion from the body without having been able to perform.

shell around it. The oil protects the bacteria within from the acidity in

SEM image of a capsule with a broken shell, revealing its interior, as

the stomach.

well as the exterior structure and the wall thickness.

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(Image: Francisco Rossier, Wageningen University)

(Image: Dr Leonard Sagis, Wageningen University)

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The group of Professor Erik van der Linden addresses encapsulation using various colloidal entities, taking into account the capsule strength and permeability, the flexibility of the composition of the interior and the use of alternative materials. One example is the use of fibrils to build the shell, creating fibre reinforced capsules. The fibrils can be made of various proteins, like BSA, alpha-lactaglobulin and beta-lactoglobulin. All three are whey proteins and can be combined with pectin, in which case the fibrils act as building blocks, while the pectin itself can be regarded as cement, keeping it all together. Microcapsule walls can be built of various types of colloidal particles and in various ways. One is when colloidal spheres are brought onto the interface

Low pH 2 Elevated temperature (80°C) (flow)

of an oil in water droplet, thus forming a layer of colloidal spheres on the oil/water interface. This

Peptites form fibrils

Protein is split into peptites

droplet is referred to as a colloidosome. Another approach is to compose a capsule of polymers and colloidal particles, each brought onto the interface consecutively by means of changing the conditions

Whole protein

Peptites

Fibrils

in solution, the so-called layer by layer technique.

Schematic diagram of the formation of long protein based fibrils by peptides that are

It was introduced for colloidal composite shells by

formed during the hydrolysis of the proteins.

Professor Julian McClements, Amherst University, USA.

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why lipids aren’t the capsule construction material of choice. If a capsule is to deliver its contents (i.e. probiotics) to their intended destination in the intestine, it must first pass through the mouth and the stomach. Van der Linden: “If you look at the requirements for such a capsule, you find that you need a composite structure in which one of the components has an elongated shape. Given the requirements, we have opted to use elongated pieces of protein, fibrils, to create these structures. The question now is how these long fibrils can be varied in length and rigidity. Can they be made as short as 10 nm, or as long as 100 µm? Which are the best proteins for the purpose? Cynthia has looked into the matter of controlling such processes. Ardy Kroes-Nijboer, who is also a doctoral student, investigated the thermodynamics of the process in which fibrils are formed. Another doctoral student is trying to find out what the membrane of the capsule should look like. The answer will be another two years in the future. There are different ways of producing such membranes, using microfluidic systems, or by means of bulk technology. This is one aspect of our task that we are investigating in collaboration with the process technology department.” All this research means that a lot of measuring needs to be done, and Van der Linden is very proud of a measuring system developed in house that can measure the length of fibrils, using optics (laser technology) and measuring techniques borrowed from rheology, which studies the flow properties of materials. The system uses existing components, but the software was developed by the researchers themselves, in collaboration with the Max Planck Institute. Van der Linden: “As it turns out, our measuring technology also comes in useful for researchers studying the properties of DNA.”


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SEM image of fibrils made from beta-lactoglobulin. These peptide-based fibrils can become tens of micrometers long and

gap

are almost stiff. They form an excellent material to reinforce capsules against mechanical breakdown. PhD student Ardy Kroes-Nijboer at work with the in-house developed rheo-optical set-up to determine the length distribution of peptidebased fibrils. The length distribution of the fibrils is important for

Hydrophobic As mentioned, proteins in a highly acidic environment (pH 2) can be thermally broken up into peptide fragments. In the case of ß-lactoglobulin, the break-up always occurs in the same spot, which is where the protein chain contains a certain amino acid, aspartic acid (proteins are composed of as many as twenty different amino acids). Not all of these peptide fragments form fibrils, as Akkermans found out. Only certain amino acid sequences (i.e. peptides with a certain sequence of amino acids) yielded the fibre-like fibrils Akkermans wanted. Most of the fragments, about 70–80% in ß-lactoglobulin, were unsuitable for the intended purpose (which is to form long, rod-shaped biopolymers). Some of the protein fragments that did form fibrils were hydrophobic and carried a very low positive electrical charge. Van der Linden: “Most globulins are partially hydrophobic. The idea is to make the pieces of fragmented protein stick together via so-called ß-sheets. The hydrophobic aspect and the low charge are essential for producing fibrils.” Cutting protein Akkermans also went in search of an enzymatic method to cut up the proteins at the aspartic acid locations. One enzyme, endoproteinase AspN (‘protein cleaver’) also proved to be capable of doing the job, but the method turned out to be a whole lot less effective than the thermal process. Akkermans: “The method produces lots of other aggregates (fragment composites; ash), which considerably reduces the yield.”

the magnitude of mechanical enforcement that is exhibited by the presence of the fibrils in the capsule wall.

Close-up of the rheo-optical set-up. To measure the length distribution a sample solution with fibrils is injected in the gap between the inner and the outer cylinders. When the outer cylinder turns, causing shear effects, a laser beam passes through the sample. The length distribution is deduced from the level of the flow-induced optical birefringence and its decay time.

A set-up to manipulate the length of the fibrils by applying extensional flow. The flow is simply realised by forcing the fibril solution through a wide tube into a narrow tube. The extensional flow profile obtained is effective in breaking up the fibrils.

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(Image: Food Biophysics (2009) 4:59–63)

(Image: PhD thesis Cynthia Akkermans, Wageningen University)

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Cumulative fibril length distribution of soy glycerine fibrils, obtained by measuring fibril lengths (N=101) from TEM pictures. The conditions of the sample: a dilution of 20 g/l protein, heated during 20 hours at

Maximal conversion of protein into fibrils as a

85 °C with shear flow at pH 2.

function of temperature, as deduced from the fluorescence intensity for various beta-lactoglobulin concentrations. Samples were stirred during heating. (Closed circles 0.2 wt%, closed squares 0.5 wt%, closed triangles 1 wt%, closed diamonds 2 wt%.) The optimal temperature for the conversion

TEM images of soy protein fibrils that were heating for 20 hours at a

of fibrils occurs at around 353 K (80 °C), coinciding

temperature of 85 °C, with shear flow and at pH 2. (a) Fibrils prepared

with the denaturation temperature of the protein.

from a low concentrated soy glychinin solution (20g/l protein); (b) fibrils prepared from high concentrated soy glychinin solution (40g/l (Image: Food Biophysics (2009) 4:59–63)

protein); and (c) fibrils prepared from soy protein isolate (40 g/l protein). Fibrillar aggregates of the potato protein patatin, prepared by prolonged heating at pH 2, which shows that other plant based proteins besides soy can be used to form fibrils.

From experiments extrapolated at zero flow, one can deduce a critical concentration of peptide necessary to form fibrils from a solution of peptides. This reveals a thermodynamic driving force behind the assembly.

The figure shows beta-lactoglobulin solutions (pH 2) heated for 24 hours at 353 K. The solutions were stirred with a magnetic stirrer at 290 rpm (open squares) during heating, stirred at 1,200 rpm (open triangles) during heating or heated at rest (open circles).

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The advantage of the enzymatic method is that it occurs in a neutral environment (pH = 7) and at room temperature. This might make the enzymatic production process of fibrils technically easier and less energy-consuming than the thermal method. Akkermans also investigated the suitability of other protein sources for the production of fibrils. Some proteins from vegetable sources, including soy and potatoes, were also found to be suitable. This is a useful result, for if fibrils were to be used as a source of meat substitutes, it would be less than ideal if they came from animal proteins. Akkermans’ first research assignment was to investigate the effect of flow on the forming of fibrils. “That’s where it all started. We found that without any flow, nothing much happens whatsoever”, Akkermans explains. “No fibrils are formed at all, only when a flow is created are fibrils formed, and rapidly. More flow means more fibrils, up to a certain point.” “It’s funny”, her former supervisor interrupts, “how this does not apply to older fibrils. This is to do with the forming of the extended structures via the ß-sheets. It takes a while to create that kind of bond.” The ß-sheets also turned out to be the place where the fibrils break if you knock them about a bit. The ultimate goal of the project is to control the length of fibrils as they are formed, in order to create an adequate container for, in this case, probiotics. Squeezing a solution through a bottleneck with some force (elongation flow, according to Van der Linden) will cause the fibrils to break at the locations of the ß-sheets, which makes this a method for shortening fibrils. Van der Linden: “The technique can also be applied to DNA.”


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lactoglobulin solutions (at pH 2) heated at (a) 343 K, (b) 358 K, (c) 363 K, and (d) at 383 K. For each temperature one observes a critical concentration of protein below which no fibrillisation takes place. The critical concentration is not dependent on temperature, thus revealing the nature of thermodynamic driving force for fibrillisation. From these data it may be concluded that the assembly into fibrils is completely entropy driven, for the case of a milk derived protein, beta-lactoglobulin.

(Diagram: PhD thesis Cynthia Akkermans / Wageningen University)

Reinforcing material Of course the purpose of the research is not solely to enable probiotics to be administered in measured doses. According to Van der Linden the research results can also be used to improve the local application of all kinds of chemicals. Research is currently being conducted on a worldwide scale into the measured release of medication. Taking drugs the usual way is like filling a cup with water by flooding the room. Fibrils could play a role in a membrane of a capsule containing medication, and all the know-how gleaned from this research project might just provide the right impetus for the development of meat substitutes. Meat, after all, is simply a clump of animal muscle fibres, and muscle fibres in turn are made up of long, fibre-like structures. In other words, just like fibrils. Van der Linden also thinks that fibrils could come in useful as materials in themselves, e.g. for use as a reinforcing material, say somewhere between graphene (a high-strength form of carbon) and glass-fibre. Or they could be used as a coating containing metal particles, to improve electrical conductivity. We havenâ&#x20AC;&#x2122;t heard the last about fibrils yet.

The protein concentration versus fibrillisation of beta-

(Image: Food Biophysics (2009) 4:59â&#x20AC;&#x201C;63)

Alive The research to tame the fibrils has laid the foundations for the ultimate goal of the project, which is to create a packaging material that can convey probiotics to their destination. This explains the interest of the industrial partner in the research project, FrieslandCampina. The company already carries probiotic drinks in its product range, and is now looking for a more effective way to get the probiotic bacteria released in the intestines while they are still alive and hence improve their healthy influence on the human body (see also the text box).

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During heating under acidic conditions the whey protein beta-lactoglobulin is cut into various peptides by hydrolysis. Only certain peptides that comply with the right charge distribution and hydrophobicity will form the fibrils. The diagram yields a schematic overview of the peptide fragments that are being formed during heating. The points at which the protein is cut are depicted by arrows. The numbers refer to the positions of the amino acids that are present in the protein. The part of the peptides that are in the fibrils are denoted by the black bars; the peptides not in the fibrils are denoted by the white bars, and the ones partially present in the fibrils by the grey bars.

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Part 2

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MST in process industry

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As a technology in the micrometre to millimetre realm, microreactors promise to bring about a true revolution in chemical process technology. As reactor vessel dimensions are reduced, chemical processes become much easier to control than they are in todayâ&#x20AC;&#x2122;s macro processes, and easier to hook up together. This will not only reduce the use of raw materials and energy, but it will also render chemical processes much more flexible making it much easier to switch from one process to another. Unlike their name suggests, microreactors are not limited to producing small quantities. In the town of Linz in Austria, the DSM company runs a plant where a microreactor produces 1700 kilogrammes of polymer product per hour. At Eindhoven University of Technology (TU/e), Professor Jaap Schouten, who is the instigator of

Photograph:Bart van Overbeeke Photography, Eindhoven

the research on microreactors in the Netherlands, is paving the way for this promising technology to reach maturity. Two spin-off companies have also been set up on the TU/e Rotating-disc reactor with inlets around the edges that can be used to introduce gases as well as liquids to

university campus.

maintain a chemical reaction. This reactor can be used for example to carry out a hydrogenation reaction, in which the gaseous hydrogen reacts with a liquid organic compound, helped by a catalyst on the rotating disc surface. The reaction produces saturated compounds, including alkanes, alcohols, and amines.

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By Arno Schrauwers


Microreactors promise revolution

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New reactor technology resembles electronics Over the years many technology revolutions have been promised but few have become reality. It was firmly believed during the 1970s and 1980s that membrane technology would revolutionise the separation of liquid fractions and that within a decade it would spell the end of the towering distillation columns that dominate the skyline of the Rijnmond area near Rotterdam. It didn’t happen. Membrane technology has remained a niche application. Nevertheless, it wouldn’t be taking much of a risk to predict that microreactor technology will not suffer the same fate. Chemical Reactor Engineering Professor Jaap Schouten of Eindhoven University of Technology remains cautious, but he will not rule out the possibility that in five years’ time microreactors will have gained a firm foothold in certain sectors of the chemical industry. And will the distillation towers be gone a decade from now? Schouten: “That is a prediction I would not dare to make.” Process intensification The Dutch government recently announced that 13.5 million euros have been set aside for an action plan aimed at the accelerated introduction of process intensification (PI) in the Dutch process industry. Microreactor technology could be considered one of the developments in this trend towards more compact process technology. Schouten confesses that he has already prepared a possible research proposal for the new programme. He’s become an expert at this. Schouten previously managed to raise research funds from MicroNed; two years ago he acquired a prestigious grant from the European Research Council, and in 2006 he was made a Simon Stevin Master, which also brought him half a million euros in research funding from Dutch Technology Foundation STW. It would seem that microreactor technology, or Jaap Schouten, is very popular with the backers. How do we know that microreactor technology or process intensification aren’t just the latest fads to come along? Schouten: “The European Roadmap for process intensification

was completed about three years ago. What’s more, the National Innovation Platform set up by the Dutch government designated the chemical industry as a key area. This new action plan has managed to establish process intensification in the Netherlands once and for all.” Conservative chemical industry Far from being dreamers, Schouten and his group of four assistants and about 20 doctoral students are intent on keeping the research as close to everyday reality as possible. “Of course you need to be at the forefront where research is concerned. You name it, we’ve done it, but practically all our projects are carried out in collaboration with the industry. The main idea is that PI is a good thing in itself, but unfortunately that isn’t really manifest in practice. Here in Eindhoven for example we have dusted off the concept of the rotating-disc reactor. Good for you, the industry says, but nobody’s using a thing like that in the real world.” The problem of course is that the chemical industry is highly conservative by nature, involving as it does major investments and long-term use of equipment and plants. Just prove to us that you can do better, is the attitude. Schouten: “That is true of course, but the industry is nonetheless prepared to participate in promising research, and they have the money to do so. I’m convinced that microreactors for example, like other new reactor concepts, will gradually manage to justify their existence. The introduction of microreactors in the current process methods and techniques is relatively easy to accept, because they take up little space and the cost remains within reasonable limits. Microreactors are scaled up by adding lots of microchannels and even entire microreactor systems together to run in parallel.” So what are we talking about? Is it about using small reactors to support the development of new processes? Or are we talking about reactors that will be used to produce large volumes? After

Today’s petrochemical industry uses large-scale installations for the cat-cracking and refinery processes. Processes like these consume lots of energy in the form of heat. Technologists agree that these processes leave much room for improvement, not just financially by keeping down the energy bill, but also in terms of sustainability. Savings in raw materials could be considerable.

In 2002 a first prototype of a microreactor was developed at the Laboratory of Chemical Reactor Engineering of Eindhoven University of Technology.

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(Images: Velocys Inc.)

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Top view of the microreactor. The reaction channel runs through the centre of the chip; the nearby platinum ‘wiring’ forms the heating

Researchers at U.S. company Velocys Inc., which develops and

element and the temperature sensors. The reactor was developed

builds microreactors, have calculated the initial cost of conventional

to measure the reaction kinetics in the partial oxidation of methane

installations for producing hydrogen by reforming methane versus the

into carbon monoxide and hydrogen, as used to produce syngas,

initial cost of microreactors offering the same yield. The conclusion is

which is used to produce clean diesel fuel by means of Fischer-Tropsch

that given the intended production capacity microreactor technology

synthesis, among other products.

is more economical. The size of the microreactor installation (on the right) is about 10 percent of the size of the conventional installation Microreactor developed

(above).

for the selective oxidation of carbon monoxide into carbon dioxide to protect the catalyst in fuel cells. The feed gas comes from a reformer in which methanol is converted into hydrogen, among other things. This gas is cooled in a heat exchanger before being fed into the selective oxidation reactor, in which CO is converted into CO2. The reactor is integrated with a second heat exchanger to keep the reaction temperature as constant as possible. In a third heat exchanger the gas is then cooled further down to 60 °C, the operating temperature of the fuel cell.

Eindhoven microreactor from 2004 for rapid testing and comparison of the activities of various catalysts for specific chemical reactions. The catalysts, e.g. various metals such as palladium, platinum, and nickel on a support, are contained in different chambers inside the reactor. Three probes in each catalyst chamber measure the gas composition in the sampling chamber at the end of the reactor. The patented flow manifold is currently being tested by a commercial partner.

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all, large chemical companies think in terms of tens of thousands, even hundreds of thousands of tonnes rather than the few kilogrammes one associates with microreactors. Schouten: “We really are talking about production on a commercial scale as well. In Linz, the DSM company has developed a microreactor together with the Forschungszentrum in Karlsruhe, replacing a 10 m³ stirred-vat reactor with a continuous-flow microreactor with a 3-litre reaction volume and a length of only 65 cm. This gives DSM a system producing about 1700 kilos of polymer product per hour. That’s a lot of polymer. The risk to DSM was fairly small because the original reactor could have been put back at any time.” Improved process control The arguments for miniaturising process technology, which involves reaction channels only a few tenths of a millimetre (i.e. hundreds of micrometres) across, lie mainly in the improved process control offered by microreactors. Schouten: “In the current conventional process equipment, reactants often fail to mix optimally due to such factors as local low turbulence levels which reduce the yield or produce products you don’t want. Safety is another important aspect since microtechnology is inherently safer than the conventional methods. The improved process control also allows us to reduce the quantity of solvent, and to cut energy costs. All in all there are plenty of reasons for using microreactor technology.” Of course there are drawbacks too. It would seem obvious that the risks of blockage in microreactors, with their narrow channels through which the liquids and gases have to pass, are much greater than they are in macro-scale chemical processes. “That is true of course”, the reactor technologist concurs, “and I wouldn’t say that microreactors provide the best solution in every case. Certain production processes are less suitable, or not suitable at all, even though an adequate solution might be found in many cases. For example, you might be able to come up with a method in which specific process steps involving solids are carried out in larger (milli) units. Or you could use what is known as the Taylor flow, in which solids are enclosed in a volume of liquid, which then flows through the small channels like a plug. What


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Professor Schouten’s group developed a microreactor for the combustion of hydrazine in 2006 as part of a Dutch-Russian NWO project. Hydrazine is used as a rocket fuel and as an emergency fuel in combat aircraft. The reactor was tested successfully by the Boreskov Institute for Catalysis in Novosibirsk.

In 2005 the reactor engineers in Eindhoven selected a new application field for the development of their microreactors. Whereas the

50 µm

previous models were restricted mainly to gas-phase reactions, the new reactors are also suitable for gas/liquid processes,

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you shouldn’t do, is replace each part in turn, and certainly not in the pharmaceutical industry, which is subject to the regulations of the U.S. Food and Drugs Administration. You will need a system-wide concept in which you invent process steps, and in which you try to avoid these kinds of problems at the early stages of reactor and process design.” According to the Eindhoven professor, microreactors open up a whole range of new applications that would be difficult or even impossible to achieve using current batch processes. “You can make do with fewer process steps because in many cases you can combine process operations, or even dispense with them altogether. In a batch process you make a certain quantity of a product, which you then store in the hope of selling it. Using continuous processes, and all microreactor processes are continuous, it becomes much easier to adapt production to match demand, you can set up closer to the customer, or even leave production entirely to the customer. Process methods and reaction steps are much easier to integrate into microreactors, for example by cooling certain sections, or by using catalysts to speed up reactions locally, depending on how the process progresses. You could use microwaves to rapidly heat up part of the process.” Seen in this light chemical technology would appear to be taking the direction of electronics, with what could be described as circuitry in which the various chemical and physical operations take place, and which can be combined as required. Schouten is happy with that analogy.

among others. These processes take place in a rectangular microchannel, in which carbon nanofibres have been grown on micropillars. The nanofibres,

3

which together represent a huge surface area, have been

Wild work In a recent interview Schouten mentioned the ‘wild work’ that every academic researcher should be doing part of the time, but the work his research group is engaged in appears to be anything but wild. It focuses on the industry, which as we have seen is rather conservative and not very keen on unexpected exploits. “I did say that, and that is what we are trying to do, but in addition we focus on the industry. After all, we are a university of technology. Here at my group we have two main research lines, or rather, three. One concerns microstructured reactors intended primarily for use in the fine chemical and pharmaceutical indus-

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The reactor engineers at Eindhoven University of Technology discovered some remarkable microscale effects in gases and liquids flowing through a shallow channel studded with micropillars.

coated with a catalyst. In this

The distance between the micropillars turns out to be a major

MicroNed-financed project Eindhoven collaborates with the

factor affecting the flow behaviour. At a distance of 17 μm between

research groups of Professor Han

the pillars the flow pattern was the same as in a pillarless channel,

Gardeniers and Professor Leon

whereas a distance of 7 μm created an irregular pattern (similar to a

Lefferts from Twente (MESA+).

trickle flow in large scale reactors).

2 µm

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Professor Klavs Jensen, the microreactor guru of MIT, foresees networks in which practically endless numbers of microreactor modules can be linked to process functions such as mixing, heating, or separation, as illustrated in this figure.

(Image: H. R. Sahoo, J. G. Kralj and K. F. Jensen, “Multi-step continuous flow microchemical synthesis involving multiple reactions and separations,” Angew. Chemie Int. Ed. 46, 5704 –5708 (2007)

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tries. Close to that is the line that researches the field of structured catalysts applied to various substrates such as carbon and foamed metal. The third research line concerns rotating reactors, in which two rotating discs or a rotor and a stator, which may be stacked, are separated by a distance of the order of 1 mm.” Accelerated transfer Aren’t chemical technologists supposed to hate things that rotate? “It may be seen that way, but chemical processes require things like pumps, which also contain rotating parts. You could combine a few process functions, and in addition it would allow you to take advantage of what would otherwise be just another process loss, like turbulence, which could be used to advantage in a chemical process to improve the mixing level or the transfer of materials. The slow transfer from the gaseous phase to the

A case in hand Flowid, Micronit and FutureChemistry, three companies that recently started as spin-offs from the universities in Eindhoven, Twente and Nijmegen, and that focus on microreactor technology, last year completed the conversion of a chemical batch process into a continuous process. In the process in question, which is known as the Paal-Knorr reaction, the reaction heat created during the conventional (discontinuous) batch processing was causing problems. Microreactor technology offers considerable advantages over discontinuous (batch) processing when it comes to process control, upscaling speed, and use of available space. In less than 200 hours the process was converted to flow chemistry on the microlitre scale, after which it was scaled up to the millilitre scale. According to Wouter Stam of the Eindhoven-based company Flowid, who is responsible for the upscaling process, this also demonstrates that

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all the reaction-related and process-related parameters are preserved, ensuring that any further upscaling to the commercial litre scale will present no problems. For this project, the Enschede-based Micronit company was responsible for the reactor design, and FutureChemistry from Nijmegen translated the batch process into a flow process. The project was a finger exercise for the trio of companies fresh from academia, but Stam emphasises that they would handle a commercial project in exactly the same way. According to the chemical engineer, there is ample industry interest in the project, in which the companies collaborated as a consortium under the moniker Access2Flow. “So far we’ve had visits from all the major chemical and pharmaceutical concerns to our application lab. The focus is on processes in the fine chemical and pharmaceutical industries.”

Part of the test facilities at the Flowid lab in Eindhoven (see also www.flowid.nl).


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liquid static hold-up, gas hold-up, gas-liquid mass transfer, pressure drop, flooding limits, bubble & slug sizes, bubble & slug rise velocities, gas & liquid axial dispersion

Liquid Gas liquid phase often holds back a process. If you can speed up that transfer, you can make do with a smaller system, sometimes as small as one fortieth of the original one. Our rotating chemical plant is an all-in-one pump cum reactor cum separator, with the rotating discs being used for all kinds of tasks. They mix, they improve the transport and therefore the reaction speed, and they separate components. In addition the discs can be used for electrochemical sub-steps in a process. In a classic process these steps usually take place in succession, but an important part of process intensification is efficient integration of process steps. We are now having a large disc reactor built in collaboration with Swedish machinery manufacturer Alfa Laval. We previously designed a smaller version by ourselves, which we had a local company build, supervised by our own workshop engineers. We took up the concept of the rotating-disc reactor ourselves, and together with a British research group we’re the only ones in Europe working on this type of rotating reactor. John van der Schaaf, an assistant professor in our group, even has the idea of building a kind of modular ‘jukebox reactor’ in which parts of the system, such as catalyst discs, can be replaced on the fly by other modules, depending on the kind of product required. We will probably be submitting another project proposal as part of the new PI programme, aimed specifically at these rotating-disc systems. Hopefully it will be accepted, and then we can move on.” Micropillars What has already been accepted is the research grant from MicroNed. In this project Schouten’s group collaborates with other parties, including Professor Han Gardeniers at the MESA+ Nanotechnology institute of the University of Twente, and the LioniX company in Enschede, which provides microsystem technology. The purpose of the research is to design what is known as a pillared microreactor, which will have a higher production speed than conventional microreactors without the pillars. As mentioned before, the speed at which reactants are transported often plays a decisive role. The question is how to get these reacting ingredients to the catalyst as quickly as possible. The pillared microreactor consists of channels studded with micropillars. Around these, carbon nanofibres are arranged onto which

Liquid

30 x 30 x 1 cm

Silicon-based microreactor, into which a micromixer (centre) and a

In 2002 the Eindhoven group started a new research line in which

reaction channel have been etched. This type of reactor is commonly

solid foam materials are used as substrates for catalysts in gas-liquid

used for experimenting with chemical reactions on a microscale. The

reactions. Solid foams have a large geometric surface area and can

reaction channels can be fairly easily coated with a catalytic coating

be made of metal, carbon, or ceramic material. They feature large

by the user.

interconnect pores measuring from 250 μm up to 5 mm across through which gases and liquids can pass. On the left is a pilot scale reactor setup in which 30 × 30 cm sheets of foam have been placed (right). Inside the reactor gas and liquid are pumped through the foam in parallel or counterflow arrangements.

nickel covered

100µm µm 100 100 µm

10 µm

Close-up view of the solid foam structure in which nickel has been deposited (left). The nickel acts as a seed onto which carbon nanofibres are grown. Gases with carbon in their make-up, such as ethene, adsorb and decompose at the nanometre-sized nickel particles, after which the carbon atoms diffuse through the nickel to be deposited on the underside of the particles, forming layers of graphite. This creates a dense ‘forest’ of carbon nanofibres on the foam substrate (‘hairy foam’; right). These fibres have a large surface area and act as a substrate for metal catalyst particles.

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Activated Activated carbon carbon Internal Internal area area

Washcoat Washcoat Flow

Flow

Pore diffusion!! Pore diffusion!! Surface In classic reactors the catalyst is contained in the pores of the Surface large area

support particles measuring from hundreds of micrometres up to

area

several millimetres across (top). This restricts the reaction between the catalyst and the liquid flowing past. On the other hand, liquid

Flow

Flow

flows relatively easily through the ‘forest’ of carbon nanofibres on the

Hydrodynamic Hydrodynamic accessibility!! accessibility!!

Only surface Only surface area

foam substrate (bottom). This brings the metal catalyst particles on area the fibres in direct contact with the flow of liquid. Recent work by the group of Professor Schouten confirms this original idea.

Hairy Foam Hairy Foam

Hairy Foam Hairy Foam

the acting catalyst has been applied. Which catalyst depends of course on the type of reaction that needs to be accelerated. MESA+ is responsible for manufacturing the reactors. Schouten’s colleague at the University of Twente, Professor Leon Lefferts, is involved in the project because of his knowledge in the field of carbon nanofibres, while Schouten and his group are doing the reactor design. Schouten: “The pillared reactor is a nice system, and you could even consider making the pillars porous so you could use them to feed gas into the reactor. This again shows the advantage of dividing the channels into sectors in which various operations or reactions take place. As part of this project we are looking into hydrogenation reactions, which are reactions in which hydrogen gets attached to organic materials, but the microreactor needs to be a generic device that can handle a whole range of different reactions.”

In 2006 Professor Jaap Schouten and Dr John van der Schaaf started a research project in Eindhoven for the development of a new type of reactor, the rotor-stator spinning disc reactor. The research is being funded from the Simon Stevin Master prize awarded to Schouten in 2006 by the Dutch Technology Foundation STW. In 2008 the

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The solid foam substrate carrying the catalyst particles can

research effort was expanded using funding from the prestigious

easily be attached to the stirrer blades in reactors. The main

Advanced Grant of the European Research Council. The top figure

advantage is that the foam stirrers can be quickly and easily

shows the rotor-stator reactor, in which a disc the size of a CD rotates

exchanged, enabling different reactions and processes to take

at high speed inside a fixed casing through which gas and liquid are

The image on the right shows a stream of gas bubbles spiralling towards the

place in succession inside the same reactor. Also, there is no

introduced. At low rotational speed the liquid between the rotor and

hub of the rotor. The bubbles are knocked away from the inlet at the edge of

need to filter catalyst particles from a slurry.

the stator clearly shows three layers (image on the left).

the disc by the rapidly rotating liquid.


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Multiple sets of rotating discs can be stacked to create a complete chemical plant on a rotating shaft. The various sets of rotating discs perform various process functions, such as mixing gases and liquids, pumping liquids, heating and cooling liquid and gas by means of

(Image: DSM)

Industry collaboration Time for the awkward question. Doesn’t the intensive collaboration with industry partners create problems for a researcher? Businesses like to keep new knowledge to themselves, whereas a researcher would rather publish today than wait till tomorrow, while doctoral students have only four years to compile their results into a thesis and take their degree. Schouten has never encountered any problems. “Of course you need to agree on things in advance, and if a business partner demanded complete confidentiality and exclusiveness, that would be a reason for me not to do the project in that way. You can think of all kinds of arrangements, because it is conceivable that a business wants to keep certain information under wraps that is crucial to their business, but not to the researcher. It’s possible. Or a business might want to use the test rig for experiments of its own. That is also possible, but in that case the business would pay the usual commercial fees. Industrial property is another aspect that requires cast-iron arrangements. We’re clear on this: we are doing scientific research, and the collaboration with a company should not be restrictive.” Collaboration is also important because Schouten’s group mainly works on experimental setups that tend to be rather pricey. “We’re talking in some cases of hundreds of thousands of euros. We don’t use computers much, because microreactors haven’t been particularly well researched yet, and the simulations don’t have sufficiently high predictive qualities. We do use standard CFD software to create the reactor design, but in the end realworld measurements will have to show how things really work.” The international acclaim for his work is illustrated by the fact that in 2005 Eindhoven was able to welcome Professor Volker Hessel of the Institut für Mikrotechnik Mainz (IMM), worldfamous in microreactor circles, as a part-time professor in Schouten’s group. Every month, he spends a week in Eindhoven. “IMM is a leading institute in Europe, and it was quite something to get him to come here. It is an implicit recognition of the work our group is doing here.”

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the discs, promoting reactions by means of a catalyst on the discs,

In its plant in Linz, Austria, the DSM company has started up a

and separating components by means of extraction or distillation.

microreactor for the production of a material for use in coatings,

Expectations are that the volume of classic reactor and separation

among other applications. In the background the old stirred 10 m³

systems can be reduced by tens of percents or even much more.

vessel can be seen, which has been replaced by the microreactor with an internal reaction volume of 3 litres. In spite of its compact dimensions of 65 × 35 × 25 cm, the microreactor developed by the Forschungszentrum Karlsruhe boasts a production capacity of 1700 kg per hour. The reactants are brought into contact with each other in many thousands of microchannels.

The production capacity of microreactors can easily be increased by stacking the reactors. This stack of 10 parallel reactors, developed and produced by the Enschede-based technology company Micronit Microfluidics, is currently being evaluated by DSM Pharmaceutical Products. The reactors contain several layers of glass in which channels have been created using lithography and powder-blasting

For more information, please contact Professor Jaap Schouten,

techniques. A thermal process finally combines the various layers into

e-mail j.c.schouten@tue.nl.

a single large reactor of 100 millilitres capacity.

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Image: Philip Broos

Close-up view of the micro Coriolis flow meter as it is currently being tested at Demcon. The tube is about half the thickness of the average human hair.

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Micro Coriolis sensor for minute mass flows High-pressure liquid chromatography (HPLC) is an analysis method used by the pharmaceutical industry to determine exactly how much of an active ingredient their drugs actually contain. HPLC is also used to test athletes for doping. The accuracy of the HPLC analysis depends on the constant flow of a solvent through the detector inside the analytical equipment. The measurement requires a changing ratio between two solvents to which the analyte has been added. The feed rate is of the order of magnitude of one gramme per hour. Researchers at the University of Twente have managed to create a silicon microstructure that does the trick. Their first demonstration version has already been completed. By Bennie Mols

Increasingly accurate analysis methods such as high-pressure liquid chromatography (HPLC), as used by the pharmaceutical industry, have

Both industry and science are constantly in need of more accurate measuring tools. Accuracy is a relative notion; what only a decade ago was considered to be state of the art would fail to raise much interest these days. Scientists and researchers in the industry are therefore constantly being challenged to raise the standard. A combination of private and public interests with Bronkhorst High-Tech BV, Demcon Advanced Mechatronics BV, LioniX BV, and Micronit Microfluidics BV on the private side, and the University of Twente on the public side, has made great progress on the road towards a flow meter that can measure less than one gramme per hour, irrespective of the type of media flowing through it. Bronkhorst is a manufacturer specialising in accurate flow meters and controllers. Demcon is an engineering firm specialising in mechatronic systems, and LioniX develops and produces microfluidic systems (as well as developing integrated optics). Micronit Microfluidics specialises in lab-on-a-chip products. Half the funding for the project comes from MicroNed, which also provides active support. Dr Ir. Joost LĂśtters is technology officer at Bronkhorst High-Tech BV, a company that specialises in developing and producing

low-flowrate mass flow meters. He explains about the growing market demand for measuring tiny mass flows: â&#x20AC;&#x153;Pharmaceutical companies for example want to know exactly how much of an active ingredient they are putting in a tablet or powder. The analytical method they use, high-pressure liquid chromatography, typically needs to be able to measure mass flows of less than a gramme per hour. Manufacturers of fine chemicals test dozens of catalysts for the car industry. They want to be able to measure all those different samples simultaneously to enable them to quickly determine which catalyst is the best. This process also calls for the ability to measure minute mass flows. The food industry wants to be able to use such small flows to enable them to extract certain ingredients from milk and use them for baby food and speciality foods.â&#x20AC;?

created a demand for flow meters capable of measuring liquid flows of varying composition. One such flow meter is the micro Coriolis sensor developed as part of the MicroNed programme. This sensor can measure quantities of less than one gramme per hour.

The micro Coriolis flow meter is a miniaturised version (based on a

Rotation of the earth Several techniques exist to measure small mass flows even lower than one gramme per hour. One common method is based on the transfer of heat. The more mass of a certain material flows through a heated tube, the faster the tube temperature will drop. The drop in tube temperature is a measure of the quantity of

different technique) of the existing mini-Cori-Flow meter marketed by Bronkhorst Cori-Tech, which can meter mass flows of a few grammes per hour. The instrument is currently in use in the food & nutrition industry, the semiconductor industry, the petrochemical industry, the pharmaceutical industry, and at university laboratories. The mini flow meter is also used in dispensing systems.

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The rotation of the Earth causes a Coriolis force as a result of which wind and water on the northern and southern hemispheres rotate in opposite directions.

Operating principle of the Coriolis force on the micro-tube. A rotation around axis ωact and a mass flow Φm induces the Coriolis force Fcor in the tube lengths at right angles to axis ωact. This force results in an additional rotation ωcor. The force is proportional to the mass flow (mg/s).

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material flowing through it. The drawback of this method is that the measuring device needs to be calibrated for every individual fluid, because the transfer of heat is medium-specific. It is much easier to use a medium-independent technique so you don’t have to know in advance what the flow contains. One example of such a device is a Coriolis flow meter, which measures the force to which a flowing medium is subjected in a rotating environment. The same force deflects wind and water flows in opposite directions on the northern and southern hemispheres of our rotating planet. This type of meter is indifferent to whether the medium flowing through the tube is a gas or a liquid, nor what its density or viscosity are. Russian oil and gas “A typical application of Coriolis flow meters is in large flows passing through large structures”, Lötters says. “The gas and oil that Russia transports to the west are measured by large Coriolis flow meters. Although the measuring principle is very elegant, it is difficult to reduce the size of such flow meters. The smaller they get, the harder it gets, but that just happens to be what we are good at.” In a small Coriolis flow meter, a gas or a liquid flows through a thin loop-shaped tube. Using an external source of vibration, a rotational vibration around an excitation axis is induced in the loop. The rotation causes the flowing medium to generate a Coriolis force. This induces an additional Coriolis rotation around a second axis, at right angles to the excitation axis. The amplitude of the second rotation is a measure of the Coriolis force. Once you know the force, you can calculate exactly how much of the medium is flowing through the tube, since the force and the flow have a known physical relationship. At the same time, the instrument measures the density of the medium.


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Basic steps of the chip manufacturing process (cross section on the left, longitudinal section on the right). Step A shows

Work of art Currently, the best commercially available Coriolis flow meter can only go down to several grammes per hour. Its loop-shaped tube measures four by four centimetres. The Bronkhorst CoriTech company launched the device in early 2008. Since there is a great market demand for equipment that can measure even smaller mass flows, the Dutch collaboration of Bronkhorst, Demcon, LioniX, Micronit Microfluidics, and the University of Twente has been working hard to produce a functional model of a micro Coriolis flow meter since 2006. The micro Coriolis flow meter consists of a rectangular, fifteen by fifteen millimetre microchip with a central cavity in which a loop-shaped tube with a length of ten millimetres is suspended. That’s where the Coriolis metering takes place. The chip also contains ducts that conduct the liquid or gas to and from the vibrating Coriolis tube, as well as the electronic connections for controlling the device and reading the results. The design and manufacture of the tube by Dr Ir. Jeroen Haneveld is a work of art in itself. The internal diameter is forty micrometres, and the thickness of the tube wall is only one to one and a half micrometres. The Transducers Science & Technology (TST) research group at the MESA+ research institute of the University of Twente manufactured the entire chip, including the most difficult component, the tube in which the Coriolis metering takes place. “We use a unique process to make the tube”, says Dr Ir. Remco Wiegerink of TST. “We make the tube from a single piece of silicon in a tightly controlled process that etches a channel with the shape of the tube interior. We then cover the channel with silicon nitride. Finally, we etch away the surrounding material, leaving a freely suspended tube of silicon nitride.”

the tube shape being etched. In step B a deposition process is used to apply a layer of silicon nitride that will later form the tube’s wall. In step C a metal track pattern is applied to the chip, and in step D an anisotropic wet etching method is used to separate the silicon nitride Coriolis tube from the surrounding material.

Scanning electron microscope (SEM) image of step B. The silicon nitride layer

SEM image of step D in the etching process. The bottom side

can be clearly seen.

of the chip shows where the Coriolis tube protrudes from the silicon.

Two-track policy Using a deposition process, a conductive layer of chrome/ 57


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platinum or chrome/gold is applied to the upper surface of the tube, through which an alternating current will later be sent. The loop-shaped tube will be suspended in a magnetic field. The combination of the magnetic field and the alternating current induces a Lorentz force in the tube, causing it to oscillate around the excitation axis. Due to the excitation rotation resulting from this induced vibration, the gas or liquid flowing through the tube generates a Coriolis force. The challenge is to calculate the force from the Coriolis rotation. If you know the force, you also know the mass flow. “We have a two-track policy”, says Ir. Rini Zwikker, senior project manager of the Demcon engineering firm. “The two tracks use a different technique to measure the deflection of the Coriolis rotation. One track uses a capacitive measuring method in which the sensor is used as a small capacitor that stores an electric charge, while the other track uses an optical detection method.”

SEM image of the completed Coriolis tube sensor. The rectangular tube is now freely suspended at a distance of only 150 micrometres from the edge of the chip.

Macro view of the freely suspended Coriolis tube with a second structure running close to it (compare with the opening photograph). The Coriolis force is read by means of applied to the two structures. The relative distance between the moving electrode and the stationary one results in a varying capacity from which the Coriolis force can be calculated.

The chip with the micro Coriolis flow meter in a test setup at the laboratory of the Univeristy of

Image: Philip Broos

a capacitive measuring system involving a pair of electrodes

Laser beam The capacitive measuring system uses electrically charged comb structures on both the loop and the box around the loop. When the combs move relative to each other, they act like the plates of a variable capacitor. By measuring the constantly changing capacity between the two combs, one can calculate exactly what the deflection of the motion is, which gives the Coriolis force and therefore the mass flow. The optical detection system uses a laser beam aimed at the tube, with the reflected light hitting a photosensitive cell. As the loop vibrates, the position of the reflected laser beam on the photo cell varies, allowing the Coriolis force and therefore the mass flow to be calculated. “Both detection methods work equally well”, Zwikker concludes. “We haven’t decided yet which of the two we will be using for the prototype of the flow meter. The technique offering the best value for money will be the winner.”

Twente. The sensor uses two permanent magnets to induce excitation by means of Lorentz forces.

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Ultimately, the flow meter will have to be fitted into a package the size of a matchbox. The trick is to seal the unit well enough from the outside world to enable a high level of vacuum to be


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The micro Coriolis flow meter with peripheral equipment in a test setup,

maintained inside, for the less resistance the loop encounters from the surrounding air, the more accurate the sensor’s readings will be. Zwikker: “We will have to optimise a number of steps before the micro Coriolis flow meter can be considered ready for production: the tube manufacturing process, the vibration induced in the tube, the vibration measurement, the calculation of the mass flow based on the vibration, and finally, the integration of everything in a small package. The measuring part is the most difficult of all these steps. We have been able to demonstrate the feasibility of the measuring principle with our demonstration version, but I think it will be at least another three years before we can develop a production prototype from this.”

with the inlet and outlet tubing attached to the underside of the printed circuit board.

For more information about this subject,please contact: Dr Theo Lammerink, t.s.j.lammerink@utwente.nl or Dr Joost Lötters, j.c.lotters@bronkhorst.com or Dr Remco J. Wiegerink, r.j.wiegerink@ewi.utwente.nl or Ir. Rini Zwikker, rini.zwikker@demcon.nl or Dr Jeroen Haneveld, jeroen.haneveld@micronit.com

Top view of the laboratory setup for optical signal detection. The Demcon engineering company is researching

Operating principle of the optical signal detection, with the light

the optical signal variant of Haneveld’s chip, as shown in the opening photograph. The micro Coriolis tube

source at the top left, and the light detector at the top right.

features an additional flap with a metal layer that reflects a laser beam. The light source is at the top left, and

The beam is reflected by the metal layer on top of the flap of

the chip with the tube is mounted on a X-Y table at the centre. The light detector and the electronics are at the

the rectangularly-shaped Coriolis tube. As the tube rotates, the

lower left.

reflected light moves across the detector.

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SEM image of a hollow fibre. Hollow fibres (made of polyether sulphone) have been in use for over two decades in ultrafiltration systems to remove microorganisms like Legionella, Cryptosporidium, Giardia, and E-coli from drinking water. Until now (SEM image: Membrane Technology Group, University of Twente.)

the fibres used for the filters had a simple circular section. The Aquamarijn company has developed a method to add a microtexture to the outside and inside of a hollow fibre, using semiconductor technology. The Membrane Technology Group of the University of Twente has produced the first test fibres. The added ribbed texture increases the filtration surface area by over fifty percent.

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Ribbed straws increase water treatment capacity These days, capillary membranes (hollow fibres) are used on a large scale to treat drinking water and industrial wastewater as well as beverages like milk, beer and fruit juices. The drawback of the current filtration systems is that they are voluminous and need frequent cleaning. Adding a microtexture to the inside and/or outside of the fibres doubles the flux, so that filtration modules can be reduced in size. This saves a lot of space, increasing the range of possible applications of membrane filters. An added benefit is that the straws are less prone to pollution. A field test will soon take place to see whether the microtextures live up to their laboratory promise... By Joost van Kasteren The plastic lunch box is filled with a jumble of what at first glance appear to be uncooked spaghetti straws. It wouldn’t be a good idea to eat them though. These straws are thin fibres that are hollow on the inside. They are plastic capillary membranes. They vary in length from a few centimetres to several decimetres, but they also come in lengths of several metres. The outside diameter is less than two millimetres, and the inside diameter is slightly over one millimetre. There’s nothing special about these straws. That is, until you look at them through a magnifying glass, for then you can see that the outside and/or the inside are ribbed. The ribs stand out about 200 micrometres. “The membrane surfaces is increased by 20 to 200 percent thanks to these microribs”, says Cees van Rijn, “which allows the flux to be increased. You can then actually purify more water with the same size filtration module.” Van Rijn, a physicist, is the managing director of the Aquamarijn company based in Zutphen, extraordinary professor of Microsystem and Nanotechnology Applications at Wageningen University, and coordinator of the SMACT (Smart MicroChannel Technology) cluster of MicroNed. Van Rijn is developing the technology for a membrane module under the auspices of MicroNed together

with the Membrane Technology group of Twente University and the Eindhoven-based Tembo company, which specialises in water treatment. It can be used to remove bacteria and other impurities from water. Other applications include the cold sterilisation of milk in the dairy industry (which will enable the taste of fresh milk to be preserved), and the clarification of lager beer.

Water treatment system in an Amsterdam 5-star hotel based on hollow-fibre technology. An increasing number of businesses and

Spinneret The physical heart of the new technology consists of the spinneret or spinning nozzle, which ensures that the straws (the capillary membranes) receive their microtexture on the inside and/or outside. The standard method for making this type of straws is to spin, i.e. extrude, a polymer solution through the spinneret nozzle, after which it enters water or some other non-solvent, causing the polymer to coagulate into what could be a fibre of infinite length. Normally the spinneret has a circular aperture with a hollow needle in the centre. When the polymer solution is fed through the spinneret at a certain pressure, this results in a hollow stream. In this case however, the spinneret features a regular series of microstructures which impart a certain surface texture to the hollow stream, which, if everything goes well, become permanent as soon as the

institutions are showing an interest in in-house filtration of drinking water. The reason is probably the series of outbreaks of Legionella poisoning in recent years, coupled with stricter legislation. The long distance between the water treatment plant at the drinking water company and the point of use increases the risk op various waterborne infections through cracks in pipes or as a result of maintenance work. The introduction of microtextures on both the outside and the inside of the hollow fibres means that a much more compact filter module can be made for the same flow rate. This brings into reach a whole range of new and cost-effective applications, in particular where space is at a premium.

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rit Filt

rix –

http

://w

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(Image: Membrane Technology Group, Twente University.)

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The Norit Filtrix ShowerFilter, a shower head featuring an integrated membrane filter module that effectively blocks Legionella bacteria. It is a prime example of the usefulness of a compact filtration module, because taking a shower (creating a warm spray) using water that has been stored at summer temperatures for extended periods, increases the risk of infection with Legionella tremendously.

Schematic diagram of a spinneret setup to produce hollow fibres with a microtextured membrane layer on the outside of the fibre. A polymer solution is extruded through a spinneret nozzle. To prevent the hollow fibre from collapsing, a needle in the spinneret injects a bore fluid. The extruded product consists of a polymer dissolved in

polymer coagulates. It is an indirect form of moulding in which the microstructure is ‘remembered’ by the liquid for a fraction of a second. To create the regular microstructure in the spinneret nozzle, Van Rijn, who used to work for Philips on the megachip project, uses semiconductor technology. The spinneret nozzle is created in a 7 by 7 millimetre square of silicon forming part of a larger wafer. First, a thin layer of chrome is vapour-deposited on the wafer, followed by a photo-sensitive lacquer, which is then exposed to short-wavelength UV light through a mask. The chrome layer in the exposed parts is then removed, after which the mask pattern can be etched into the silicon. “We use a special technique for this process”, Van Rijn says, ”deep reactive ion etching, that allows us to achieve nice straight edges. The method uses a plasma, a white-hot gas, containing radicals of sulphur and oxygen. The sulphur radical converts silicon into silicon hexafluoride, which escapes as a gas. The oxygen radicals block the reaction slightly. Depending on the gas flow rate and the ratio of sulphur and oxygen radicals, you can create walls that are straight as a die, or inclined inwards or outwards. It gives you very accurate control over the process.” In this case the technique is used to create serrations with a depth of approximately 500 micrometres. The last step is to break up the wafer into dozens of silicon nozzles, which are then mounted in the spinneret.

an organic liquid (e.g. polyether sulphone in NMP). The extrusion involves three physical processes: 1) As soon as the polymer leaves the spinneret nozzle, part of the End view of the demonstration module in which the hollow fibres have been trimmed and embedded in resin.

solvent will pass through the outer wall of the hollow fibre, while another part will be absorbed on the inside by the bore fluid. 2) In addition, water will enter the fibre through the gaseous phase (air gap) and the coagulation bath on the outside, and from the

Demonstration model of an ultrafiltration module in which hollow

bore fluid on the inside of the fibre. This results in the formation of

fibres have been bundled in a cylindrical casing. This results in a high

polymer-rich and polymer-poor areas that determine the way the

fibre density, which allows for high flow rates.

fibre’s pores are formed. During the extrusion process, a relatively compact, microporous membrane skin is formed around the outside of the fibre, which determines the greater part of the filtration properties. The size of the pores can be controlled to a large extent by varying the width of the air gap. 3) In the rinse bath the fibre solidifies, and the last traces of the solvent are removed.

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Hollow needle The semiconductor technology is used to create the part of the nozzle that produces the minute protrusion on the outside of the straws. It still leaves the inside of the straws smooth. To create the ribbed interior, the hollow needle fitted at the centre of the nozzle must also be given a microstructure. The solution Van Rijn came up with is as elegant as it is effective. “We take a section of hollow polymer fibre that has already had the ribbed microtexture applied to the outside. Onto that we then grow a layer of metal, nickel to be precise, and then we dissolve the polymer. This leaves a hollow needle with the microstructure we need to apply the ribbed microtexture to the insides of the capillaries.” Using advanced semiconductor technology, Van Rijn has managed to create a nozzle with microstructures of the order of magnitude of 200 micrometres. The disc itself is slightly over half a millimetre thick, and the nozzle measures 1.2 millimetres across.


Van Rijn: “Many people at first thought it would be impossible to create such small structures, but fortunately they’ve been proven wrong. Even so, I have to admit that it wasn’t quite as simple as it seems because the whole process is extremely precise.” Phase transition The spinneret is already being used to produce many metres of hollow fibre at the Membrane Technology Group of Twente University, which participates in MicroNed’s Microfactory Cluster (MUFAC). The process is basically the same as the method used to produce smooth hollow fibre, which is by means of phase separation. Dr Rob Lammertink, a lecturer at the department, explains how the process works. “Normally you prepare a solution of polymers including polyether sulphone, or a mixture of polymers in NMP (N-methyl-pyrrolidone). The solution is then extruded through a nozzle, with the resulting stream passing through water. The solvent dissolves in the water, but the polymer doesn’t. As a result, the polymer and NMP mixture becomes increasingly saturated until the polymer coagulates and solidifies. A phase transition process like this is known as immersion precipitation. The remarkable thing is that the transition from polymer in solution to solid polymer takes place relatively gradually.” At the boundary between NMP and water – solvent and non-solvent – a skin is first formed, with relatively small pores. As you go deeper into the material, the pores increase in size because the solvent disappears less rapidly. The result is a membrane with pores that increase in size as you go deeper below the surface. Lammertink: “You could say that the skin, which is only a single micrometre thick or less, forms the actual membrane, with the rest of the polymer acting as a supporting structure.” Pressure drop As mentioned before, this extrusion technique is used on a large scale to produce the hollow fibre and capillary membranes that are used in water treatment plants and in kidney dialysis machines. According to Lammertink, the new spinneret microstructure creates a much larger membrane surface area without increasing the pressure drop across the membrane. The pressure drop is caused by the resistance offered by the skin. At the top and sides of the ribs, the skin thickness is the same – approximately one micrometre – as in the rest of the membrane surface. This increases the active surface

(Image Membrane Technology Group, Twente University)

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To reduce the flow resistance of hollow-fibre filters, part of the MicroNed programme involved new research to find methods of increasing the membrane surface area of the hollow fibres. The Aquamarijn company used semiconductor technology to produce a

Schematic diagram of a spinneret.

spinneret that can be used to create a microtexture in a hollow fibre.

“The better an innovation matches the market, the better its chances of success” Professor Cees van Rijn: “The challenge for microsystem technology is to keep making systems smaller while maintaining their level of functionality, so processes can become more cost-effective. Creating a microtexture inside a hollow fibre for example increases the surface area per kilogramme of raw material used for the membrane. What is very important if an innovation is to succeed, is that you leave its embedding unchanged as much as possible. In the case of microfiltration we tried to keep the fibre material, the production parameters, and the membrane specifications the same wherever possible in order to ensure they match what is already commercially available. This ensures that the end user market accepts the innovation with relative ease. The new filtration modules are also cheaper to produce. Dr Tammo Bieze of the Tembo company adds: “The added value of this product is that you can now build smaller filtration modules. This is a major advantage in

Tammo Bieze and Cees van Rijn

applications where space is at a premium. It also takes less material (polymer) to produce a filtration module. And smaller filter systems not only help keep down the cost of regular maintenance, they also require less rinse water and energy, which not only helps to cut costs, but also reduces the impact on the environment.”

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(Image Membrane Technology Group, Twente University)

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Cross-section of an extruded fibre. The SEM image clearly shows that the air gap was relatively short, as the microtexture has been very well preserved.

Macro image of a spinneret created by means of deep reactive ion etching. The etching agent is a plasma containing radicals of sulphur and oxygen. The sulphur radical converts silicon into silicon hexafluoride, which escapes as a gas, while the oxygen radicals block this reaction, as it were. By varying the etching temperature and the ratio of sulphur and oxygen radicals, walls can be

Professor Cees van Rijn’s ‘lunch box’ with extruded microtextured fibres.

SEM-opname: Membrane Technology Group, Universiteit Twente)

(Photo: Membrane Technology Group, Universiteit Twente)

created that are perfectly vertical.

Close-up image showing the production of

a hollow fibre with a microtexture on its outside. The pore size and the pore density of the membrane layer are determined to a large extent by the time it takes to cross the air gap between the spinneret and the coagulation bath (usually between one millimetre and a few

SEM image of a cross-section of the outer layer of a hollow fibre. The

centimetres). As a result of surface tension the microtexture tends

layer on the lower right is the actual membrane layer or skin. The

to flow back to the circular shape (without the added texture), but

skin has a higher density, but with lots of 10-nanometre pores it is

this process can be slowed down by increasing the viscosity of the

very porous. The more coarsely porous inside acts as a supporting

solution, or by reducing the surface tension of the material.

structure for the skin.

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area at least twofold. In other words, you can push twice the usual volume through the straw. The properties of the membrane, such as thickness and pore size, can be controlled in a number of ways. The number of pores can be controlled by adding an extra polymer to the solution. The concentration and temperature of the polymer solution also affect the membrane’s properties. In addition, the distance between the nozzle and the non-solvent in which the polymer coagulates, determines how well the microtexture is retained. If the air gap is too wide, the microtexture is lost and you end up with standard hollow fibre membranes with smooth insides and outsides. Cleaner Measurements taken by Lammertink and his group show that the microtextured capillary membrane performs much better than expected. Not only does it double the volume of medium treated per unit of membrane surface, as foreseen, but it also stays much cleaner than a smooth membrane does. Lammertink cannot provide an answer yet to explain this phenomenon. “It could well be that the microtexture affects the flow of the medium, breaking up the boundary layer between the liquid and the membrane, which may prevent any pollutants from adhering to the walls. A similar phenomenon could also be caused by variations in the polymer skin’s thickness, but we’re still looking into this. Anyway, the result is a more heterogeneous flux through the membrane, which has a positive effect on membrane pollution.” Whatever the case, the favourable properties of the microtextured capillary membrane (higher flux, less pollution) are excellent reasons for investigating the membrane’s behaviour in a practical context. “The idea is to use the membrane fibre to remove bacteria and sediments, and possibly flocculated iron oxide”, say Tammo Bieze, a physical chemist and the owner-manager of Tembo, a company that supplies systems for purifying drinking water and industrial waste water. Applications include the removal of pathogens such as Legionella or Cryptosporidium from drinking water, but also the extraction of proteins from process water so the water can be reused elsewhere on the premises, e.g. as rinse water. Growing market “Water treatment is a rapidly growing market”, says Bieze, “and membranes play a key role, not just on a large scale, as in drinking water treatment plants, but also on a smaller scale in hotels, hos-


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Close-up view of a spinneret with a microstructured hollow needle

Cross-section of the microtextured hollow fibre as produced by the

used to produce a hollow fibre with a microtexture on the inside. The

spinneret shown above. The final diameter is determined by the

hollow needle is made using a 3-D galvanic growing process specially

shrinkage resulting from the coagulation and the force with which the

developed for this project. The substrate is a hollow fibre with a

fibre is pulled through the coagulation bath.

microtexture on the inside which will later be etched. (Image Membrane Technology Group, Twente University)

pitals, and even households. Industries are also showing a growing interest in water because it is becoming increasingly expensive to produce water, and also to discharge it. The main advantage of a microtextured membrane is that you reduce the size of your system by half. This means that it takes up less space, making it more attractive to smaller industrial users and households. You could even have systems that treat the water at the point of use, e.g the shower head, or the kitchen tap, as well as point of entry systems.” The great advantage of using a membrane at the point of use is that it allows you to customise the purity of the water to match its intended use. Bieze: “Only a few of the 120 litres of water we each use daily is used for drinking water. We use some 50 litres for showering. Water needs to be free from certain bacteria, like Legionella, as otherwise the warm spray during a shower could be life-threatening. The remaining 60 litres are used to flush lavatories and doing the laundry and dishes. Even so, all our water gets purified to drinking quality standard. In the Netherlands we can still afford to be inefficient where drinking water is concerned, but in other countries where water is scarce and often polluted, a differentiated approach would be more suitable, and people would benefit enormously from a point of use water treatment system. We have been thinking about reusing the water from our showers, by the way. You could have a button to flush away the water containing soap and shampoo, and then you could recycle the much cleaner shower water for a longer comfort shower, without causing too much of an impact on the environment.” All in all the future bodes well for the ribbed straws, although they still have to live up to their promise. Thanks to the MicroNed research we now know that semiconductor technology can be used to produce a nozzle that can create microtextures in a capillary membrane. Which just goes to show once again that innovations take place where different technologies meet.

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For more information about this subject, please contact Cees van Rijn, +31 575 519751, e-mail ceesvanrijn@aquamarijn.nl, or

Cross-section of a hollow fibre,

Rob Lammertink, +31 53 4892063, e-mail r.g.h.lammertink@tnw.utwente.nl or

showing a microtexture on both

Tammo Bieze, phone +31 73 6579381, e-mail tammo@tembocorp.nl.

the outside and the inside. The macroporous wall oup, Universiteit Twente)

contributes greatly to reducing the flow resistance.

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The production process of powdered milk uses a lot of energy, and the structure of the granules is difficult to control. The shape, size, and density of the granules have a marked effect on the productâ&#x20AC;&#x2122;s solubility and on the quantity of powder that will fit into a bag. Physicist Albert Poortinga wondered whether inkjet technology had any solutions to offer. To find out , Friesland Foods, recently renamed FrieslandCampina, collaborated with the TNO research establishment. The principle of milk jet technology was tested as part of the MicroNed programme. As it turns out, the successful prototype of the TNO designed spray nozzle is capable of producing not only highly uniform granules of milk powder, but also granules with (Photo: TNO Industrie & Techniek)

special content, like fish oil. by Marion de Boo Test setup for the production of highly uniform granules of (milk) powder using a spraying head developed and scaled up by Friesland Foods and TNO, based on inkjet technology. (Image: TNO Science & Industry)

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Milk powder from a print head

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Inkjet technology controls shape, size and density of granules

Dairy giant FrieslandCampina has been producing different kinds of powdered milk in its towering spray-drying structures for decades. It is an excellent way to preserve the nutrient value of fresh milk. “Those metal spray-drying towers stand five to six floors high and are about eight metres across”, says Ir. Jasper Vollenbroek, senior researcher of Process Technology at FrieslandCampina in Deventer. “At the top of the tower, the milk is injected as a spray of very fine droplets. Hot air of almost 200 °C is pumped through to evaporate the water, and at the bottom end the milk simply descends in the form of powder.” Milk powder can be kept for extended periods and takes up little volume, making it easy to transport all over the world without the risk of deterioration due to bacteria. Fresh milk contains 12 per cent of dry solids, whereas milk powder is 97 per cent dry matter. To reduce the energy consumption of the process, the milk is first condensed in a drop flow by means of direct contact heating on a steel surface. The process efficiently removes the water from the milk and allows much of the heat to be recovered. This makes the evaporation process fairly low-energy, but it is the final stage when the condensed liquid is turned into powder that uses such a lot of energy. Originally the milk was sprayed into the top of the drying tower using a fast rotating spray wheel. Over the last few decades, high-pressure sprayers have also come into use. These spray the condensed milk into the drying tower through a small hole at high pressure, forcing it into turbulence. The shear stresses this induces in the milk cause the product to explode into myriads of minute droplets. “The problem is that it is a largely uncontrolled process”, says dairy specialist Vollenbroek. “It produces large and small droplets, round and elongated ones. We’d love to gain better control over the results. In late 2005 a colleague of mine, Albert Poortinga of then still Friesland Foods, had the bright idea of looking at inkjet technology. Something like an inkjet print head could possibly be used to turn dairy products into powder. It is an excellent method

Schematic diagram of the filter mat spray drying system at Meppel-based Friesland Foods Kievit.

of producing droplets with a more homogeneous size distribution.” To minimise the packing volume, i.e. to have the least possible quantity of air between the granules, the particles need to be cubic. However, that would pack them tight like a block of concrete, and it would be impossible to prise them apart. To make sure the dry product will flow smoothly, the particles should be as round as possible. Rapid Manufacturing During a brain-storming session with TNO Science & Industry in Eindhoven, an establishment FrieslandCampina has been collaborating with for years in many fields, a link was established between Rapid Manufacturing (TNO knowledge) and the concept of milk jet printing. The two parties decided to join forces in a project funded by FrieslandCampina. The first test proved to be an immediate success, says Ir. René Houben, senior researcher of print technology at TNO Rapid Manufacturing. TNO has the pro-

Top view of the filter mat spray drying system at Friesland Foods Kievit. The pipes leading to the spraying heads can just be made out at the top of the tower.

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Conventional spraying heads at Friesland Foods Kievit. Each head can atomise a couple of hundred litres per hour.

Components of a conventional spraying head. The liquid becomes turbulent in the chamber on the left and is then atomised through the holes in the cover.

Close-up view of a conventional spraying head as used in the drying tower at Friesland Foods Kievit.

Example of a product obtained using the conventional spray-drying method. The variation in particle size and shape is typical.

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duction technology to build products for various kinds of partners directly from 3-D CAD data. “You design a product on your computer”, Houben explains, “and then you simply click ‘print’ to have the product manufactured layer by layer. The operating principle is rather like that of an inkjet printer, but we work in three dimensions, and we use different types of materials, which can be hard or more flexible.” The jet technology is fast and flexible, and dispenses with the need to make a mould for a prototype. The required data comes straight from the design process. However, it is a bit tricky to render functional materials using the available conventional jetting systems. The viscosity of the materials soon becomes too high, causing the print head or nozzle to become blocked. TNO had just finished developing a new, improved nozzle to deal with this problem, when FrieslandCampina dropped by. “Condensed milk is a highly viscous material”, Vollenbroek says. “If a liquid is too thick, you can’t just turn it into powder because it comes out of the pressure nozzle as a gluey stream. Condensed milk with a dry matter content of over 55 percent and a viscosity in excess of 300 to 350 millipascal second is difficult to spray. Our current spray-drying systems have reached that limit.” According to Houben a lot of energy could be saved by further condensing the milk to increase the dry matter content before it is turned into powder. “Given the right nozzle you could raise the viscosity to 500 millipascal second. It would also enable us to fine tune the size of the droplets.” Fine dust The current milk powder production process results in a wide range of droplet sizes. “The smallest droplets turn into dust particles that remain floating in the drying air, flying all over the system and sticking to everything. Filters are constantly getting blocked”, Vollenbroek says. “It also lowers the yield. It may only be a loss of the order of magnitude of a few tenths of a percent, but when you’re producing several tons of milk powder each hour, the numbers add up. Fine


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dust also introduces the risk of explosion. It only takes a spark to make the whole lot go bang. Finding a solution to the fine dust would be a major step forward. It would also enable us to reuse the drying air more efficiently.” “Inside an inkjet print head, a piezoelectric crystal vibrates constantly. This induces a perturbation in the flow of liquid, causing the jet to break-up”, Houben explains. “This creates a series of droplets, rather like opening a water tap just a tiny bit and then tapping it with your finger, creating stable drop formation.” As the vibration frequency of the piezoelectric crystal increases, the droplets become smaller. Accurate control of the droplet size would be very useful to the dairy technologist, as it would enable him to produce all kinds of special products, which could contain dried probiotic bacteria to stimulate intestinal flora for example, or fish oil. Stringy bits Early in 2006, a research trainee in Eindhoven started on a twoyear project funded by MicroNed. Within a year he had demonstrated that the concept was feasible. Houben: “We didn’t know what to expect – the milk could have started to curdle, or we could have ended up with stringy bits rather than droplets if the milk had started to dry too quickly before it had been turned into droplets. But it all worked perfectly – albeit at a rate of millilitres per minute. We tried using increasingly viscous materials, and the results were good.” Apart from the viscosity, the temperature of the milk feed, the vibration frequency, and the size of the jet nozzle also are important parameters in the new process. Vollenbroek: “When milk is exposed to high temperatures for longer periods, the proteins in the milk can become denatured. They will then start to stick to the equipment, causing pollution. The process starts at temperatures at low as 65 °C. This is why the nozzle has to be made to very high standards. For example, it needs to be suitable for sterilisation if it is to be used in a dairy process.” Initially the nozzle produced fairly large droplets about 170

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Stacked bags of powder at the production facility of Friesland Foods Kievit. The shape and density of the granules greatly affect the quantity of product that will fit into a bag. Apart from lowering the cost, a reduced volume could also lessen the impact on the environment caused by transport.

Inkjet head from a DeskJet 510 printer. The viscosity of the ink in a head like this is extremely low compared with the viscosity of condensed milk products ready for spray-drying. Clearly, upscaling was called for.

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Drop generator

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Charge electrode

micrometres across (one micrometre is one thousandth of a millimetre), but the principle had been demonstrated nonetheless.

Gutter High voltage deflection plate

Paper (Image: TNO Science & Industry)

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The principle of an inkjet printing system as featured in many consumer printers. The only component used for the spray-drying application was the droplet generator.

Rapid manufacturing setup at TNO Industry and Technology, based on

(Image: TNO Science & Industry)

(Photo: TNO Industrie & Techniek)

inkjet technology.

The atomiser developed by TNO can handle high-viscosity liquids and turn them into 3-D end products. (Image: TNO Science & Industry)

Close-up view of the atomiser. The jet consists of droplets that can be controlled individually. They are selected or discarded by selectively

Rayleigh break-up FrieslandCampina and TNO then jointly continued to further develop the technology. More sophisticated nozzles have now been designed, capable of producing much smaller droplets. “We call this method of producing droplets the Rayleigh breakup”, the nozzle specialist says. “It has been in use for some time in inkjet printer systems, but in foodstuffs technology this is a revolutionary development! And, considering the cost of a spraydrying tower, the added investment is minimal.” According to Vollenbroek it will all depend on how long the new system will last, how reliable it will be, and how much maintenance it will require. “That still remains to be seen. If we have to down production every five hours to do maintenance, it will cost us a lot of money. On the other hand, if we can produce tons of milk powder at a stretch without any downtime, we will save lots of money.” Reduced energy consumption is a major argument in favour of the new method. According to the laws of physics, a pound of steam can be used to evaporate a pound of water. At the milk powder plant, energy is continuously recovered by using the residual heat from the milk evaporation process to heat up a pipe in the next stage of the process. The process has been so cleverly linked together that a single pound of steam will suffice to evaporate six to seven pounds of water. Inside the dying tower the efficiency is much lower, with the process often requiring as much as two pounds of steam to evaporate a single pound of water. The wet drying air (approx. 80 °C), which is now lost at the end of the process, could perhaps soon be reused once it no longer contains fine dust. It is another factor that makes the milk jet technology highly promising.

applying an electric charge to them so they can be deflected by electrostatic means.

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Patent TNO already held a patent for the nozzle system based on inkjet technology. TNO and Friesland Foods have jointly applied a


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patent for the use of the spraying head for drying purposes. And what will be the benefit for the buyer? Vollenbroek: “Nice, round, monodisperse particles like these slide easily past each other. They flow more smoothly and don’t form lumps like a product containing lots of dust will do. Coffee creamer will also become much easier to pour from its sachet. We will also soon be able to coat all kinds of sensitive probiotic bacteria more carefully to protect them so they will survive their stay in the spray drying system. We will be able to create a whole range of new specialties, including powders enriched with encapsulated fibres, iron, or calcium.” Meppel-based company Friesland Foods Kievit specialises in the encapsulation of ingredients for the foodstuffs industry, and is also looking into the use of printing technology for this purpose.

(Imag

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Macro image of granules with uniform particle size, produced with inkjet technology.

Demonstration product made using rapid manufacturing inkjet technology and composed from various different materials. This object demonstrates that this technology can be used to gradually build up 3-D shapes.

Image: Friesland Foods

Scaling up The system is now being scaled up. An important question is how close together the nozzles can be placed without interfering with each other’s spray. The shapes of the droplets are being studied by means of a stroboscope, which can take razor-sharp images of the droplets, even though they race past at a rate of 20,000 per second. Much of the research took place using a solution of maltodextrin, by the way. Maltodextrin produces a clear solution and has a less complex composition than opaque milk which contains various types of fat, proteins, and carbohydrates. So when will the system become operational? “We can now process about 80 litres an hour”, Vollenbroek says. “That’s not enough to feed a large milk powder plant, but it is already starting to become commercially attractive for the production of specialities.” For further information about this subject, please contact Dr Tom van Hengstum, phone +31 570 695 904, e-mail: tom.vanhengstum@frieslandcampina.com, or Ir. René Houben,phone +31 40 265 0122, e-mail: rene.houben@tno.nl

Diagram of granule size distribution (conventional and new methods).

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Part 3

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MST for high-tech industry

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Researchers at the University of Twente and printer manufacturer OcĂŠ are trying to work out how inkjet droplets are formed. They are studying how small air bubbles inside the ink channel can disrupt the forming of droplets, and how inkjet droplets are formed at the print head nozzles. The behaviour of air bubbles and the development of droplets can be visualised using various optical and acoustic techniques. The results are compared with theoretical and numeric flow models. By Bennie Mols Making prints using inkjet printers has by know become a well-established technology, but much higher print speeds and even smaller droplets to raise the print quality to an even higher level require a Image: Philip Broos

lot of scientific research. Venlo-based printer manufacturer OcĂŠ has been researching this field for the past decade together with the Physics of Fluids department at the University of Twente. This setup is used to study the forming of individual droplets in an inkjet print head.

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Faster, smaller, more accurate inkjet printers Dutch company Océ is one of the world leaders in the design and manufacture of wide-format printers for professional use. Wide formats are used to print technical drawings for use in production, architecture, and construction, as well as other graphical representations, including maps, advertising posters, and art. One of the Océ showpieces for wide-format printing is the Océ ColorWave 600 inkjet printer, which was entirely developed within the company. Just like any inkjet printer, the Océ ColorWave 600 also projects small droplets of liquid ink onto paper. The ink is inserted into the printer in the form of solid spheres, so-called TonerPearls, contained in cassettes. The TonerPearls, a concept developed by Océ, come in four colours: cyan, magenta, yellow, and black. Using combinations of these four colours, the printer can produce any required colour on paper, a method used in many printing processes. The Océ ColorWave 600 contains eight print heads, two for each colour. When the solid ink particles are heated inside the print head, a gel-like ink is produced that fills the reservoir of the print head. The heads are then passed across the paper at high speed as they squirt the ink onto the paper. The TonerPearls are formulated to ensure that the ink droplets remain compact and become fixed very rapidly. This prevents the ink from bleeding and produces the best print quality on any type of paper. Acoustic waves Each of the eight printer heads in the Océ ColorWave 600 contains 256 small channels that carry the ink to the same amount of nozzles. To print the ink onto the paper, each channel is equipped with an elongated piezo element positioned against the ink channel (8 millimetres long). Driven by an electric pulse, the piezo element vibrates up and down at a high frequency, periodically narrowing and widening the channel. Rather than acting directly on the ink the way toothpaste is squeezed from a tube, the rapid changes in shape induce a pattern of acoustic waves in the ink channel. The acoustic waves make the ink flow,

causing the channel to fire up to twenty thousand 30-picolitre ink droplets per second at the paper. The ColorWave 600 can print two A0 sheets per minute (an A0 sheet measures about 1.2 × 0.8 metres). Unlike laser printers, this printer does not produce ozone or unpleasant odours, nor does it become polluted by printer toner. It is also unlike thermal inkjet printers, which use a thermal element inside the nozzle to heat water-based ink very rapidly producing a vapour bubble that ejects the droplets. The advantage of piezo inkjet printers over thermal inkjet printers is that the ink does not have to be water-based. The TonerPearl ink contains no water or solvents and will therefore not dry out and clog the nozzles, something that could happen in other inkjet printers. Once the ink is on the paper, a temperature-controlled gelling and solidification process takes place.

Océ builds industrial printers, like the Océ ColorWave 600, one of their showpieces. The machine has a print speed of two A0 sheets

Air bubbles The inkjet process is one of the most reliable techniques available to produce droplets, but there are still times when the process becomes disrupted. One of the possible problems is that an air bubble can be entrapped at the nozzles. The entrapped air can then end up in the ink channel in the form of small air bubbles. This disrupts the droplet-producing process and at worst can result in a temporary nozzle failure. That is a nuisance but, depending on the application, the deficiency can also be totally unacceptable. The latter is the case in new applications of inkjet technology that are increasingly being diverted from the traditional process of printing on paper, to the printing of electronic circuits and DNA micro-arrays, where a single incorrectly printed droplet is inadmissible. To better understand how inkjet droplets are formed and find out more about the malfunctions that sometimes occur, Océ has been collaborating for over a decade with the Physics of Fluids department of the University of Twente, a group of some forty researchers led by Professor Detlef Lohse. On the Océ side, researcher Hans Reinten coordinates the collaboration.

per minute, requiring almost 1,000 million accurately aimed droplets of identical size. Such large-format machines are typically used in the advertising industry, by architects and construction companies, for posters, etc.

Instead of using water-based ink, Océ developed so-called TonerPearls for the Océ ColorWave 600. These melt inside the print head at a temperature of 130 °C before they are fired at the paper. Once the droplets hit the paper, they become permanent in a matter of seconds.

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Reservoir

Each print head contains 256 channels, each of which is individually controlled by a piezo element. The element 10 mm

Piezo

Channel block

induces a pressure wave in the channel, the top end of which is connected to a reservoir, while the bottom end finishes in a nozzle. A

Nozzle plate

single channel can generate

Nozzle (Ø 30 µm)

approximately 20,000 30-picolitre droplets per

Droplet

Console with the eight print heads of the Océ ColorWave 600, which

second.

“Our common interest in air bubbles formed the basis for our collaboration. The knowledge we have gained about the behaviour of air bubbles has been of great importance for improving the reliability with which the Océ ColorWave 600 prints its droplets. We have also used this knowledge to develop PAINt, a built-in and unique nozzle-monitoring system that includes both the hardware and the software, and which checks all the nozzles every second for the presence of air bubbles inside the channel.” The PAINt technique uses the piezo elements also as sensors, to detect any change in the channel acoustics. When an air bubble is detected inside a channel, the system automatically takes action, e.g. by temporarily disabling the channel to enable the trapped air to dissolve. The research is ongoing.

uses two 150 DPI print heads for each colour. Smart positioning of the print heads means that a resolution of 300 DPI per colour can be

Progress of pressure wave inside the ink channel Reservoir

pulse

achieved.

1 time 3

Nozzle

5 1

2

3

4

5

6

Diagram showing the progress of the pressure waves inside the print head as a result of the contractions of the piezo element (left), and the progress of the electric pulse energising the piezo element (right). First the piezo element contracts (1), producing pressure waves in the direction of the nozzle and in the direction of the reservoir (2). The

“A better understanding and control of the way droplets are formed should eventually result in even faster, more reliable, and more accurate inkjet printers”, Reinten says. “The trend is to create even smaller droplets and fire them at even higher frequencies. Smaller droplets enable you to print at higher resolutions, so with more detail. And increasing the frequency speeds up the printing process. We are trying to expand the envelope. However, practice shows that as the frequency increases, so does the risk of air bubbles.” How exactly does air get entrapped? How do air bubbles affect the channel acoustics? How do you design a print head that does not entrap air bubbles? How can you prevent an entrapped air bubble from becoming a problem? And how do ink droplets develop as they leave the nozzle? These are some of the concrete questions the researchers at Océ and the University of Twente are working on.

reservoir acts as an open end, as a result of which the reflected wave receives a positive amplitude. The nozzle acts as a closed end, so the amplitude of the reflected wave does not become inverted (3). When the returning waves (4) arrive at the centre point of the duct, the piezo element moves in the opposite direction (5), producing another positive pressure wave. The sum of the travelling waves is a positive pressure wave in the direction of the nozzle (6). The travelling time A single Océ ColorWave 600 print head. The feed chute for the

of the waves depends on the effective speed of sound in the duct.

TonerPearls is on the right.

Accurate timing of the edges of the piezo pulses creates the right acoustics to produce the ink droplets.

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Dirt particles In 2006, University of Twente doctoral student Arjan van der Bos started his doctoral research into the stability and dropletforming properties of inkjet print heads. A major part of the research comes under the MicroNed programme. “When I started, two other doctoral students were in the end stages of their research”, Van der Bos recalls. “Jos de Jong was studying the entrapment of air using experiments, and Roger Jeurissen was doing the same using analytical and numeric models. I built on their work.”


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De Jong was the first to demonstrate that the entrapment of air bubbles has two possible causes. The first is that small pieces of dirt, such as a bit of dust or a flake of skin, can reach the nozzle through the surrounding air and disrupt the forming of droplets, which facilitates the entrapment of air. The second is that a thin layer of ink can then form on the nozzle plate, which can lead to the entrapment of air. Both mechanisms were discovered by the doctoral student when he studied the air bubble using an indirect method. He used the piezo element as the driving mechanism for squirting the ink and as a microphonic sensor to monitor the acoustics in the ink channel. The acoustic pressure pushes on the piezo element and this can be measured in the form of an electrical signal. Comparison between signals with and without air bubbles reveals the signature of the presence of air in the ink channel, as it were.

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A barrage of ink droplets produced by 10 adjoining nozzles of a ColorWave 600 print head. All its 256 channels are capable of producing exactly the same droplets over and over again at high frequency. Individual droplets can reach speeds of almost 7 m/s.

Glass channel De Jong also mounted a small glass connecting channel directly in front of the nozzle, aimed a high-speed camera at it, and recorded the growth of the captured air bubble together with the forming of ink droplets. This enabled him to make the bubble and its absolute size visible for the first time. Doctoral student Roger Jeurissen modelled the behaviour of an air bubble inside the channel. Among the effects he identified were the dominant physical effects of this process: the compressibility of the air bubble, the mass inertia of the ink, and the viscous friction of the ink inside the nozzle. He took into account the fact that the bubble moves and that its size oscillates under the influence of the acoustic waves in the channel. The bubble’s oscillations in their turn affect the channel acoustics and consequently the movement of the ink in the nozzle.

Detail of the monitoring setup at the Physics of Fluids department. The microscope is used in combination with a powerful flash source or a high-speed camera to create detailed images of the droplet-forming process. When the print head vaporises ink during tests, the ultra fine droplets are removed by the grey extractor system. The Brandaris 128 camera can capture up to 25 images per second. Such high speeds are necessary because the entire droplet-forming process takes only 20 microseconds.

Various test setups have been constructed at the Physics of Fluids department of the University of Twente to study the forming of inkjet printer droplets in close detail. For his research, doctoral student Ir Arjan van der Bos uses an optical microscope and high-speed cameras. His objective is to find a way of improving the forming of smaller and

Controlled air entrapment Van der Bos took up the experimental work where Jos de Jong had left off. “Initially I looked only at the entrapment of air”, the doctoral student says, “but since 2008 I have also examined the way inkjet droplets are formed.” Whereas his predecessor had not yet looked for a relationship between the acoustic signal measured by the piezo element

faster droplets. The evolution of a droplet. Reading from left to right, we can see how a droplet emerges from the nozzle and forms a long tail. Once the tail has separated from the meniscus, it is retracted into the main droplet. One of the parameters being investigated at Océ and the University of Twente is how far it can contract the tail before it breaks up in several places at once.

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Piezo

U

Ua

1

Rp

2

A

If

Another part of the research conducted by Arjan van den Bos concerns the stability inside the ink channel. He produces exotic droplets to capture an air bubble under controlled conditions. This series of images shows how an air bubble

The piezo element can be used to induce a vibration

has just been captured by the nozzle. Images 1 and 2 show how the tail of the

in the channel wall to build up a pressure wave but

generated droplet separates, having drawn the meniscus out with it. In images 3

with a small adjustment to the electronics can also

and 4 a new small droplet appears to be forming on the meniscus, but this fails to

measure the pressure on the piezo element (and

separate. As the meniscus is drawn out further (5 and 6), we see that an air bubble

therefore the channel) as well.

has been trapped in the centre of the meniscus (7) and is being drawn into the nozzle with the meniscus (8). Piezo signaal [mA]

Actueren (signaal uitsturen)

Luisteren

0

25

Luisteren

50

75

Luisteren

100

125

150

Tijd [µs]

A glass channel block was placed between the ink channel and the nozzle plate

The acoustics in the channel can be measured

to study the effects of an ingested air bubble in greater detail. Each channel is

by continuously switching the piezo element

shaped like an hourglass, with diameters of approximately 300 μm. Transparent

between pulse generator mode and microphone

ink has been used to clearly show the ingested air bubble, which measures about

mode during printing. By listening in on the

120 picolitres, at the bottom right. The edges of the adjacent channels can just be

printing process, Océ can detect anomalies such as

made out on either side of the channel.

contaminations or bubbles with great accuracy, and so find out exactly when a channel stops printing correctly.

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and the camera recordings of the glass channel, Van der Bos did exactly that. As it turned out, the behaviour of a captured air bubble is actually very predictable. “Once an air bubble has been ingested, it takes up a preferred position, after which it starts to grow. Once the bubble has grown big enough, it prefers to move to an angle in the channel, where it is surrounded by as many walls as possible. The location and the volume of the bubble are directly related to a certain disruption of the acoustics.” In this way, Van der Bos was also able to demonstrate that even very small air bubbles cause a measurable disruption of the acoustics. “By linking the experimental results directly to the numeric calculations, we were able to demonstrate how the acoustic signal of the piezo element can be used to detect small bubbles long before they grow big enough to disrupt the forming of droplets.” It also turns out to be possible to control the print head with a special pulse that always results in the entrapment of air bubbles. It is precisely this controlled process that allows the entrapment to be studied in detail. Van der Bos shows a recording of an entrapped air bubble that moves in the droplet for a while, exactly in the middle of the nozzle. The recording is perfectly sharp. “We gained control of the entrapment process by generating exactly the right kind of actuation pulse. It was a pure case of serendipity, as happens so often in science.” Van der Bos is holding back his final conclusions on the entrapment of air bubbles until he has also completed the necessary numeric simulations to verify his experimental results. “Nonetheless”, the doctoral student says, “the crux will be that at the moment the tail of the droplet is about to leave the nozzle, a certain disruption of the meniscus movement causes air to be entrapped. This kind of disruption can be caused by particles of dust that happen to pass by.” Peering through silicon Observing the air bubble through the glass channel has a drawback, though. The glass channel sits between the nozzle and the ink channel. And although the glass inset is only four tenths of


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MEMS technology for piezo inkjet print heads

Piezo signal [mA]

0.05

0

−0.05

−0.1

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50

100

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150

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The acoustic signal of a channel in the print head with the glass channel block changes in the presence of abnormalities. The reading (represented by the blue line) shows how the acoustics of a normal channel appear during the printing process. The red line shows the acoustic signal with an air bubble trapped inside the same channel. The signal’s amplitude and frequency have changed. The Physics of Fluids department first modelled exactly how the air bubble affects the acoustics, and subsequently verified this using optical and acoustic measurements. 12 10 8

Height [µm]

a millimetre thick, it results in a slightly longer channel than the original one in the inkjet print head. Wouldn’t it be possible to look through the nozzle plate to watch the behaviour of the air bubble? The problem is that this plate is made of nickel or silicon, which are not materials you can simply see through. “Even so, we thought it had to be possible in the case of nozzle plates made of silicon”, Van der Bos says, “but instead of using visible light, it would have to be done with infrared light, which has a somewhat longer wavelength. To find out if this approach would yield results, graduate student Tim Segers spent three months of his internship doing research at Océ Technologies.” Segers did his research on an inkjet head made entirely of silicon. Although current print heads, like those in the Océ ColorWave 600, are made of graphite (with a nickel nozzle plate), the R&D department at Océ is working on a new generation of inkjet heads made of silicon using MEMS technology (see text box). MEMS technology can be used to make the ink channels much smaller and set them closer together. This will make the print heads even more compact and economical, and it will enable them to fire smaller droplets at a higher frequency than the current graphite-based heads can. “The problem with infrared observations is that silicon has a very high refractive index”, Segers explains. “This means that a relatively large portion of the light gets reflected internally instead of passing through the material, which makes it harder to see what is happening inside. The only way to avoid this problem is by pointing the camera at the nozzle and the silicon plate straight from below, and that is how we managed to use infrared light to watch an air bubble in the ink channel of a working, unmodified printer head.”

6 4 2 0

To record the air bubble’s behaviour in the silicon ink channel, Segers illuminated it with stroboscopic infrared light. Because the silicon MEMS print head is so much smaller than the current graphite-based inkjet head, most of the physics now takes place in shorter scales of length and time. The frequencies are higher and the bubbles are smaller so they dissolve more rapidly. Together with the infrared observations, Segers also recorded the acoustic signal from the piezo element.

0

50 Radius [µm]

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During his doctorate research Roger Jeurissen modelled the behaviour

MEMS technology is becoming increasingly important for future generations of piezo-driven inkjet print heads. Techniques pioneered in the microchip industry are being used to create and machine silicon on wafers. This technology lends itself much better to miniaturisation than conventional machining methods do, because the production costs are related to the area of silicon being used. This means that the use of existing and fully developed standard processes and tools makes smaller dimensions and smaller droplets cheaper. The MEMS technology has long been common practice for manufacturing thermal printer heads. For piezo inkjet heads the techniques hangs on the integration of piezo material onto silicon wafers, but the relevant developments have been picking up speed in recent years. In the Océ ColorWave 600 print head the central section consists of separate manufactured components: a graphite channel block, two pieces of film, two actuator plates with piezo elements, and a nozzle plate. The central assembly measures about 10 × 10 × 40 mm. For comparison, Océ researcher Hans Reinten shows a silicon chip measuring about 25 × 5 mm. “This chip contains the same functionality as the core of the graphite print head. The only difference is that six different parts need to be glued together to make a single graphite print head, whereas a single wafer produces one hundred of these chips”, Reinten says.

of an air bubble inside an ink channel. The figure shows the stable and unstable points of equilibrium of an air bubble (red) in the channel. In many cases the air bubble is expelled together with the ink, but it can also end up in the angle of the channel, where it disrupts the printing process.

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“Buy comparing this signal with what we observe in the stroboscopic recordings by the infrared camera, we can accurately describe the bubble dynamics and the effect on the channel acoustics. The main difference with looking through a glass channel modification is that the geometry of the original situation has been preserved. We are now busy comparing the acoustic signal with the data from numeric models.”

Wafer with the new generation of print heads developed at Océ.

Macro image of the new MEMS print heads. The copper-coloured

The nozzle end of the new MEMS print heads. The small opening of

squares are the piezo elements, which are also used to drive the new

the nozzles is almost visible.

design. Each element corresponds with a single channel. Smart design strategies are used to maximise the nozzle density.

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Droplets Having researched the ingestion of air bubbles, in 2008 Van der Bos also started to study the forming of the ink droplets below the nozzle. After a short retraction of the meniscus, the ink is projected from the nozzle with a peak velocity of some fifteen to twenty metres per second. The high velocity does not last long, and only a few microseconds later the ink in the nozzle is already moving in the opposite direction. The result is a spherical head with an elongated tail. The tail becomes more and more constricted, and finally breaks. If all goes well, the tail then catches up with the round head, and they merge into a single, perfectly spherical droplet of ink. The driving force behind the constriction of the droplet’s tail is the ink’s surface tension, but this effect is opposed by the ink’s inertia and viscosity. High speed versus high resolution Van der Bos used three optical techniques to research the droplet formation: high-speed imaging, stroboscopic imaging with a lowspeed camera, and finally, single-flash recordings. A high-speed camera lets you see how a single droplet develops. Although the camera is good at freezing the droplet’s motion in the frame, the drawback is that the camera resolution is not as high as that of a low-speed camera, so the fine detail is lost. It is sometimes better to use a low-speed camera for processes that are perfectly repeatable in an experimental setting. Then you can have a single nozzle produce a thousand droplets that are illuminated by a stroboscope. If the stroboscope is flashed at exactly the same frequency as the droplets are produced, you get a series of almost identical images of the droplets. All these images can then be combined into a high-contrast image that is the sum of thousands of droplets. Since each of these droplets behaves in almost


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A exactly the same way as all the others, the result represents a high-contrast image of a single droplet in motion.

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During his internship

Piezo actuator ink flow 2

at Océ, University of Twente Student Tim Segers tried to find out how air bubbles might

Six-nanosecond laser flash Finally, Van der Bos also used a technique known as single-flash photography. This uses a very bright and short flash of light to illuminate the moving droplet, resulting in a perfectly frozen image. Van der Bos used laser light with an exposure time of six nanoseconds. Van der Bos: “We used three different techniques to enable us to determine the droplet’s velocity at various points in its trajectory. By doing so at consecutive moments, you get a detailed view of the way the droplet is formed and the tail gets constricted. One of the phenomena we hope this helps us to understand is the breaking up of the tail into several satellite droplets. This is an unwanted process that can occur when you’re trying to create increasingly smaller droplets at increasingly higher frequencies.” The long-term collaboration between Océ and University of Twente has yielded many new insights, according to Océ researcher Hans Reinten. “In particular the quantification of parameter areas, in other words defining which combinations of parameters occur with such and such phenomenon, is very useful when designing new inkjet heads. Our own research tends to be rather more phenomenological and pragmatic. The University of Twente is able to add a more fundamental research component. We now know much better than ten years ago which mechanisms play a role in the entrapment of air, the behaviour of air bubbles in the print head, and the way the droplets themselves are formed.”

also affect the MEMS

3

print heads. He used an infrared camera and an infrared light source,

4 Nozzle wafer

which can be used to

5

see through silicon.

B Side view (A) and bottom view (B) of a MEMS ink channel.

2

3 4

The ink flows into

5

the channel from the

Infrared image by Segers, with the microscope

top (1) and enters the

aimed at the piezo element and perpendicular to

actuating chamber (2)

the nozzle plate. The image shows the nozzles of

in the channel (3). At

two adjacent channels, the funnels, and the flow

the end of the channel

channel beyond. The piezo element can also be

are a funnel (4) and the

seen in the background. The channel is surrounded

nozzle (5).

by a ridge of adhesive.

Nozzle plate 54.7˚ Infrared camera Segers saw that the high refractive index of silicon (n ≈ 3.4) meant

For more information, please contact:

that the critical angle between air and silicon is about 17°. This causes

Hans Reinten, e-mail hans.reinten@oce.com, or

almost all angled surfaces to act like mirrors to the infrared light. The

Arjan van der Bos, e-mail j.a.vanderbos@utwente.nl.

figure shows how a print head was modified to enable infrared light to

An air bubble could be observed using an infrared

Van der Bos hopes to gain his doctorate in late 2010.

be used to see inside the funnel.

camera to see inside an active print channel. The image shows how the air bubble is pressed against the ridge of adhesive inside in the channel.

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Mechanical engineers at TU Delft have built the first prototype of a micromilling machine with non-contacting magnetic bearings. These bearings have the potential to make the micromilling machine more accurate than conventional ones fitted with ball bearings, and enable a very high rotational speed in the absence of mechanical contact. An unexpected spin-off was the creation of a new type of high-speed clamp, which was exactly what a manufacturer of micro gas turbines was looking for. By Bennie Mols

Detail of a micromilling setup with a magnetic bearing. The cutting head of the cutter measures 0.2 millimetres. Micromilling processes currently use machines designed for macromilling, but these machines tend to be heavily Image: Philip Broos

constructed and limited in their dynamic possibilities. They are also unable to achieve the high rotation speeds required. Magnetic bearings can be used to improve the functionality of micromilling machines, e.g. by measuring the force exerted by the cutter on the manufactured object, or vice versa.

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Improved micromilling machine

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Smart tool clamp for extremely high milling speeds is patented As the semiconductor industry continuously works on reducing the size of microchips in two dimensions, so the mechanical manufacturing industry is always on the lookout for ways to create even smaller material structures in three dimensions. One example of a miniature creation of this kind is a chemical microreactor featuring minute channels. The big advantage of a microreactor is that it takes only tiny quantities of chemicals and energy to produce the desired chemical reactions and to study the process (see also the article on microreactors elsewhere in this book). Microscale reactions are also more efficient and easier to control. Another example of a three-dimensional miniature structure created by the industry is in the manufacturing process of an optical lens, which requires the milling of a hard metal mould. This is done using a large milling machine fitted with a microcutter. The spindle is powered by a motor fitted with a controller that usually allows speeds to be reached up to 40,000 rpm, which is exceptionally high. To enable the machine to cut away exactly the right quantity of material in exactly the right spot, it needs to control the position of the cutting head very accurately. In traditional milling the required accuracy is achieved by making the milling machine bigger, heavier, and more rigid to reduce any elastic deformation. Increasing the mass and therefore the inertia of the spindle also makes it more difficult to move it out of position during the milling process. Using a heavy, rigid machine for micromilling has several drawbacks, however. In the first place the introduction of a microcutter with a very small diameter means that the system as a whole can no longer be considered rigid. In the second place a larger and heavier machine is unwieldy. What you want is a small, light machine that uses less power and takes up less space. In the third place you have no control over the milling process other than through the cutter’s rotation speed and the force applied to push the cutter into the material being milled. You have no idea of the forces acting on the cutter during the milling

process. If you had, you would be better able to prevent cutters from breaking or being worn down too far. In the fourth place the milling speed is limited by the fact that the spindle and the bearings are in physical contact with each other. Higher speeds means higher temperatures, and more wear and tear. Finally, there is the positioning accuracy of the cutter, which is limited by the restricted accuracy of the ball bearings, which always have some degree of play in them. Non-contacting rotation Doctoral student Ir Maarten Kimman – with MicroNed funding – and his supervisor lecturer Dr Ir Hans Langen have created a prototype of a micromilling machine that avoids the drawbacks of using a microcutter in a traditional milling machine. As far as is known, it is the first working prototype of a micromilling machine with active magnetic bearings. Kimman and Langen both work at the Faculty of Mechanical Engineering (3mE) of TU Delft. “Rather than making increasingly bigger machines for micromanufacturing, we aim to make smaller, smarter machines”, project leader Langen explains. “The main challenge is to avoid the problem that a smaller machine is inherently less rigid and therefore less accurate.” The basis for the solution to this mechanical problem lies in a combination of mechanics, electronics, and control: mechatronics. Langen explains: “The idea is to no longer physically support the spindle using bearings, and instead rotate and control it in a non-contact environment. This can be done by applying the right kind of electromagnetic field in the gap between the rotor and the stator. A smart design enables the mechatronic system to continuously monitor and correct the position of the rotor. This needs to be done because a magnetic bearing is inherently unstable. A non-contacting rotor has the added advantage that the rotor itself is not subject to mechanical wear.”

People all over the world are conducting research to find the optimum conditions for micromilling machines, determining the best milling speeds and the best cutter geometries, measuring the forces involved in the cutting process, the optimum cutting depths, and heat production. Typical applications include the production of very small moulds (i.e. for manufacturing Philips hearing aids) and the direct production of minute objects such as gear wheels and microreactors.

Microreactor milled at TNO Industry, Eindhoven, using a conventional milling machine.

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A microcutter shown next to a human hair. The term microcutter covers cutters with a diameter of between 0.1 and 0.5 millimetres. These are made of carbide and have a protective coating.

Some milling machines for cutting details with sub-micrometre accuracy have already been marketed, but they still follow the same design philosophy as macromilling machines, using ball bearings or air bearings, a heavy construction, high mass, and high rigidity. Researchers at TU Delft think that small objects could be more easily made using smaller and smarter milling systems. The magnetic bearing has an active control system so the position of the shaft within the bearings can be accurately controlled, allowing the milling of Control

objects at a slight angle, for example.

Diagram of system controlling the magnetic bearing of the micromilling machine. Suspending the rotor in a magnetic field without any physical contact with its surroundings avoids all friction between the shaft and its environment. At right angles to this view, another control system is active. The axial direction of the shaft is controlled by measuring the axial movement on top of the shaft using a non-contacting position sensor. Electromagnets are then activated to apply a force to the disc halfway along the shaft.

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Doctoral student Maarten Kimman designed and constructed the first prototype over the past four years. Standing by his machine he explains how the prototype works: “The microcutter is held in a specially designed tool holder which in turn is clamped onto the long, cylindrical rotor. The noncontacting assembly rotates in the electromagnetic field that is created using permanent magnets and coils. The material to be milled is mounted rigidly on a table that is moved below the cutter in a computer-controlled process.” The prototype uses a commercially available microcutter with two cutting edges and a cutting face diameter of 0.2 millimetres. The rotor is over ten centimetres long, its position is continuously measured and controlled by the combination of permanent magnets and coils. The gap between the rotor and the emergency bearings is 0.2 millimetres. This small amount of leeway offers the additional capability of having the rotor move out of centre, giving the cutter a translation as well as a rotation, which can be useful for certain applications. First test Most of the doctoral student’s effort went into the design of the spindle. Kimman: “The spindle contains active magnetic bearings rather than the mechanical ball bearings you will find in traditional milling machines. When the material is being cut, a force is applied to the cutter. This displaces the rotor, and this movement is measured in the bearings. Our control system responds to this movement by calculating on the fly how much current needs to be sent through the coils to produce exactly the right amount of counterforce to make sure the cutter stays in position.” The active magnetic bearing developed by the Delft researchers measures the position of the rotor 20,000 times per second, and adjusts the rotor position in what is practically real time (the bandwidth is 400 hertz). Although active magnetic bearings have been in existence for some time, this is the first time that such a non-contacting bearing has been integrated in such a small micromilling machine. Kimman tested his prototype for the first time in June 2009. “During the first test there were five people watching the machine eagle-eyed”, Kimman recalls. “We use a clear plastic hood to cover the machine during the actual milling, just in case


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something goes wrong and the cutting tool or bits of material get hurled around. Fortunately all went well. At a speed of 80,000 rpm we cut a small groove in a piece of brass. We then inspected the cut under a microscope, and it looked good. The data the active magnetic bearing provides about the cutter position and the currents in the bearings gives us a lot of information that we can use to optimise the milling process in the future.”

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Section through the upper radial bearing of the Delft micromilling machine, in which permanent magnets are used in combination with electromagnets. Magnetic bearings are usually magnetically pretensioned by having a base current flowing permanently through electromagnets. This makes the positioning of the shaft easier to control. The use of permanent magnets reduces the power consumption and heat dissipation of the micromilling machine. Shaping the bearing so that the pretensioning flux passes axially through

Resonance frequency An added benefit of reducing the size of the cutting spindle is that it shifts the inherent resonances of the spindle to higher frequencies. Resonances during the milling process are the last thing you want, as they affect the quality and accuracy of the milled surface. In the micromilling machine built by Kimman and Langen the rotor only weighs 180 grammes. The very compact spindle design has moved the first resonance frequency to approximately 3.5 kilohertz, which is very high when compared with conventional equipment. “During the milling process it is essential to keep as far away as possible from the resonance frequencies”, Kimman says. “In the classic milling machine without the magnetic bearings it is not uncommon to find vibrations at higher speeds due to system resonance.” Kimman intends to raise the test speed of 80,000 rpm to even higher values, but for reasons of safety has not tried this yet. “With the current prototype we have already reached a speed of 150,000 rpm without doing any milling”, the doctoral student says. “Ideally we would like to achieve a rotation speed of 500,000 rpm, as that would give us a cutting speed comparable to those in macro systems.” Patented clamp An unexpected spin-off of Kimman’s research is a new design for a cutting tool clamp, the physical connection between the cutter and the rotor. Since the Delft researchers are working with high speeds, the tool clamp must be capable of withstanding enormous centrifugal forces that try to hurl the tool clamp’s matter away from the centre of rotation. In the worst case scenario, the tool clamp will simply disintegrate. Kimman says: “We have prevented this by cutting three T-shaped slots in the tool clamp. The slots are designed to create a lever

the rotor (indicated in blue), minimises the losses arising from changing magnetic fields in the rotor. The control flux is indicated by the red arrow.

Whereas the spindle of a conventional milling machine can weigh several dozens of kilogrammes, the spindle of the Delft micromilling machine is only 13 cm long and weighs no more than 180 gram. Electromagnets positioned on either side of the disc enable the height of the cutter to be accurately controlled. The thicker section on the shaft is the rotor of the synchronous motor, which consists of two magnets that are held in place by a strong fibre covering capable of resisting the centrifugal forces created by the high rotation speeds. The black bands at the top and bottom are the wear-resistant layers of the emergency bearings.

Sample sheet showing the various types of vibration affecting the spindle. As it spins up to high speed, the rotor encounters several areas of resonance frequencies. The quality of the manufactured result is severely affected by milling at speeds too close to a resonance frequency so knowledge of these frequencies is very important. The first resonance frequencies are determined by the control bandwidth of the magnetic actuators, and can therefore be controlled. Sectional view of the magnetically suspended shaft Axial bearing First radial bearing

Motor comprising the stator and the permanent magnets on the rotor

Second radial bearing

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The completed milling machine mounted on

Close-up of the rotor of the upper radial bearing. The air gap between the rotor and the

a vertical rig, used to set the rough cutting

stator can clearly be seen. The spindle speed is measured by means of the black and white

depth. The object is held by an X-Y positioning

surfaces on top of the shaft. The signal is used to compensate gyroscopic effects that start

table controlled by Lorentz actuators. The

to play a role at high speeds (in this case, 150,000 rpm). The axial movement is measured by

table was supplied by NXP/ITEC, where it was

means of the sensor fitted to the top of the shaft.

used in a wire bonding machine.

The first milling experiment, during which a 0.2-mm wide cutter was used at 80,000 rpm to remove 5-µm thick layers of brass at each pass. The result shows clean circles and a track that is exactly 200 µm wide, showing that no unwanted resonances occurred during the The first milling experiments.

milling process.

Front view of the test piece.

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action when the clamp rotates. As the centrifugal force acts on the tool clamp, the lever action ensures that the inner part of the clamp is pressed inwards rather than outwards. This means that the inner wall of the tool clamp is pressed firmly against the cutter, preventing it from coming unstuck. The design is unique enough for us to apply for a patent.” By coincidence the researchers were introduced to a manufacturer of micro gas turbines, Micro Turbine Technology BV. (MTT), while they were working on the project. The company is marketing a miniature combined heat and power system that will enable households to generate their own electricity. Such a system involves coupling a micro gas turbine to a microgenerator. The rotation speeds in the system are so high that the coupling between the turbine and the generator also suffers from the effects of high centrifugal forces. “The solution we came up with for our own coupling turned out to be exactly what this manufacturer also needs”, Kimman says. Spark machining “We will now subject the prototype to a wide range of experiments, and compare the milling results one by one with those of larger micromilling machines, as far as possible”, project leader Hans Langen explains. “What is the quality of the milling result? How deep can the machine cut? What are the maximum speeds it can handle? How fast does the material need to be moved under the cutter? These are all questions that we would like to see answered in detail by experimental results. In addition, the signals we measure in the magnetic bearings enable us to listen in on the milling process, as it were. We hope to be able to improve both the machine and the process dynamics by unravelling these signals.” This means that their work on the micromilling machine is by no means finished yet. One of the next objectives is to use the same micromilling machine for an entirely different type of manufacturing process known as EDM (Electrical Discharge Machining). In EDM a pulsed voltage is applied to a pair of electrodes, the shaping electrode and the object to be manufactured, and the resulting spark is used to eat away the material. The process takes place submerged in a bath filled with a dielectric material. Once the critical voltage is reached, a spark will jump the gap between the shaping electrode and the object. The discharge


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EDM used on a piece of stainless steel. The brightly lit area above the metal is the plasma channel being The Delft scientists also intend to use

rapidly switched on

the micromilling machine for an entirely

and off.

different type of machining process, Electrical Discharge Machining or EDM. EDM involves a pulsed voltage being applied between a shaping electrode and the object to be manufactured, both of which are suspended in a bath filled

Illustration: Rob Luttjeboer/TU Delft

is so intense that it creates a plasma channel between the electrodes inside which the pressure and the temperature are high enough to melt and evaporate material at both ends. The temperature and pressure drop in between the voltage pulses causing the plasma channel to implode and ejecting the molten material from the original material. “We could in fact already use the microcutter in our milling machine as an electrode”, Langen says. “We could start by cutting a slot, which we could then finish in the same machine using spark machining. It would enable us to combine the speed of the milling process with the surface finish of the EDM process. In spark machining, it helps to move the electrode in a spiral-like way. This creates better flushing conditions and improves the end result. And thanks to the non-contacting magnetic bearing in our machine we can create the spiralling movement by making the cutter rotate just out of centre.” Another challenge will be to further reduce the size of the micromilling machine as a whole. This will involve miniaturising the spindle, which contains the permanent magnets and the induction coils, in particular.

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with a dielectric material. Once the voltage is high enough, a spark jumps the electrode gap, creating a plasma channel between the electrodes. The pressure and the temperature inside the plasma are high enough to melt and evaporate material at both ends. The plasma channel implodes in between the voltage pulses, ejecting the molten material from the original material and the wire to be carried off by

1

2

3

For more information, please contact

the dielectric. The pulse frequency setting depends on the

Ir Maarten Kimman, e-mail maarten.kimman@asml.com

material to be machined. Dr Langen expects to be able to

In the first rough

In the second

In the last step

move from micromilling to EDM in three steps:

step the material is

step the cutter

the original milled

milled.

is finished using

cut is precision-

micro-EDM. This

machined, with

removes only a

the spindle not

Kimman’s patented cutter mount for high-speed use. This unexpected

To be able to insert a cutter into the mount and

minimal amount

only rotating, but

spin-off resulted from the search for a suitable tool holder that could

secure the latter to the milling spindle, Kimman

from its diameter,

also making a

withstand the extreme centrifugal forces affecting any rotating mass.

also had to design a special mounting tool that

just sufficient

vibrating motion

In conventional cutter mounts this causes a reduction of the clamping

pushes the three masses inwards to

to create a

induced through

force, whereas Kimman’s cutter mount causes the clamping force to

open up the triangle inside the

perfectly circular

its bearings to

increase as the speed rises. The purpose of the slot in the middle of

mounting.

circumference with

improve the

the cylinder is to

its centre exactly

finishing process.

compensate for

on the rotation

any differences in

axis.

diameter between

The cutter mount is a monolithic structure consisting of

the cutter and the

a triangle to which three masses are attached though

rotor.

levers. As the centrifugal forces push the masses outwards, the walls of the triangle are pushed inwards.

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If a robot places resistors on a

lack of the pasteâ&#x20AC;&#x2122;s damping action makes the placing process go haywire. The components start to bounce, become unstuck and end up in the wrong place.

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Image: TNO Industry and Technology

printed circuit board without the usual soldering paste, the


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Smart construction stops components bouncing TNO BlueBird project paves the road for stacking chips Most electronic components are still gently placed in a soft bed of soldering paste on a printed circuit board before they are soldered in place. The advent of microsystem technology (MST) has thrown a spanner in the works, however. MST components of various, often fragile materials cannot resist the heat of the soldering process so they have to be fixed in place using a thin layer of adhesive. The components are placed by a gripper, and in the absence of the damping paste hit the board quite violently and then bounce all over the place. As part of a MicroNed project, TNO Science and Industry painstakingly investigated the placing process and developed a patented gripper capable of placing MST components carefully and accurately. Equipment builders are now applying for licences, and the knowledge gained from the research results comes in very useful for the BlueBird project, which seeks to further increase the density of ICs by stacking A modern production line at NeWays in Son en Breugel (close to

microchips. This ambitious initiative from the desk of TNO is to take the Netherlands to the forefront of the back-end of

Eindhoven). The printed circuit board first receives an application of soldering paste and then a series of pick & place machines position

the semiconductor industry.

hundreds of different components on it. A continuous-feed oven then solders the components in place. At the end of the chain each circuit

By Hans van Eerden

is fully tested.

The assembly of electronics and microsystems involves gripping small components from a tray or a roll with a vacuum gripper, moving them to the correct location, and finally, placing them in position. The pick & place process had to keep being speeded up under pressure from the never-ending demand to cut costs in the market for professional and consumer electronics. It was all right as far as microelectronics were concerned. These components are soldered in place using soldering paste â&#x20AC;&#x201C; it spreads like peanut butter, but without the crunchy bits â&#x20AC;&#x201C; and this paste is screen-printed onto the printed circuit board. Acting as a damper, the paste softens the landing and ensures correct alignment of the components during placing and soldering. In sort, it makes the assembly run smoothly. 89


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The printed circuit boards are positioned under a mask, and then a very carefully measured layer of soldering paste is applied by a doctor blade. The printed circuit boards, with soldering paste applied, are fed through a pick & place machine from left to right. The front of the machine holds several rolls of components ready to be picked & placed.

The soldering paste forms thousands of little islands that will later form the connections between the components and the conducting tracks on the PCB. When the components are placed onto the PCB, the paste has a very welcome side-effect as its damping properties absorb the impact energy of the placing process. This stops the components from being damaged. It has also enabled the pick & place speed to be raised for years on end without complications.

Suppliers deliver the components on spools of tape. The protective film is removed by the feed systems so the components can be easily picked up by a suction device attached to the robot.

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Controlled collision Back to microsystem technology, which covers a much wider application range and is still gaining terrain by great strides. Microsystems like airbag sensors, hearing-aid microphones or the focusing unit for the camera in a mobile telephone, all contain components of a variety of materials, including silicon, which go up to make the fragile MEMS (Micro Electro Mechanical Systems). The lenses are made of plastics which arenâ&#x20AC;&#x2122;t heat-resistant, so they cannot be soldered and require the application of adhesive. Unfortunately the adhesive layer tends to be too thin to offer any protection when the components are placed, so the gripper simply smashes them into the surface. The alternative, with the gripper releasing the components just short of the printed circuit board, doesnâ&#x20AC;&#x2122;t work either, as the parts will then simply flutter along the surface, completely ruining the accuracy of the placing, and turning the whole exercise into an uncontrolled process. Releasing the components in exactly the right position (just touching the printed circuit board) isnâ&#x20AC;&#x2122;t yet a feasible option because of the uncertainties in the dimensions of the components and the imperfectly smooth surface or downright wavy one on a microscopic scale. So the logical choice when placing components is to go for head-on though controlled collisions. The problem is that a collision causes a reaction. With the component pinned to the printed circuit board by the gripper the whole assembly can start to vibrate, and even before the gripper retracts, the components will bounce back up again. This rebound effect interferes with the accuracy of the placing process, and it can also cause damage to components. Impact research TNO Science and Industry presented itself as the party to investigate the wild pick & place process in order to gain better control and ultimately improve the MST assembly process. Ing. Erik Puik of


the Micro Devices Technology department became project leader for the MicroNed-project ‘Impact Research for Micro-Assembly’. Puik: “At TNO we had already started cataloguing the available gripper technologies during the preliminary stages of the MicroNed programme in 2004. That resulted in a clear definition of the bouncing problem, which formed the basis for the second phase of our research, the MicroNed project that was launched in 2006.”

enable it to pick up a wide variety of components.

The components are moved to the placing position via the shortest

(Photocredit BOSCH )

route.

(Photo: Assembléon, Veldhoven)

Machine-gun The credo was, better find out first what is going on. “We built a sophisticated machine with a simple stick (a hollow needle that uses vacuum to pick up components; Ed.) to simulate the rapid placing of components. That machine was capable of accelerating and decelerating at a whopping 60 g (1 g is the acceleration caused by the Earth’s gravity; Ed.). Watching it work was like seeing a machine-gun in action”, Puik says. Existing pick & place machines had never been built for applications like this, so they weren’t rigid and fast enough, according to Puik. “We had to eliminate these weaknesses from the measuring system purely to investigate the process itself.” Using a high-speed camera (in black-and-white, to get the highest possible speed) the placing process was recorded with an unprecedented resolution (a pixel size of about 5 micrometres). The companies involved in the project, such as Besi and Assembléon (ex-Philips), also had cameras like these, Puik knew, but they used them on their existing machines with the weaknesses mentioned. Puik: “That’s why they failed to get to grips with the process. When we told them what we were doing, they were flabbergasted and envied us because we could spend a few years getting to the bottom of the matter. We were able to see what was going on much better and that enabled us to draw much better conclusions.”

The robot is fitted with a number of different suction devices that

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(Photo: Assembléon, Veldhoven)

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In modern products such as cars, computers, and mobile phones, adhesives are increasingly being used as many components require no electrical connections...

The pick & place machine has access to an extensive data library containing details of the printed circuit board design and the components to be placed. Before being placed, the position of each component in the suction gripper is checked using a fast camera. The position of the printed circuit board is permanently set at the start of the feed process, so the robot has all the information it needs to position the components in exactly the right location.

... or simply because they don’t contain any metal, such as these lenses for mobile phone cameras. A product-specific pick & place machine stacks lenses before they are glued together using a lowviscosity adhesive in a capillary bond.

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There is an ongoing battle to increase the feed rate of components.

components reach the PCB surface. This needs to be limited if the

The continuously improved performance of modern servo systems

components are to survive the impact forces.

has made it possible to keep on speeding up the pick & place process.

A considerable amount of time could be saved if the approach speed

The bottleneck is now being formed by the speed at which the

could be increased.

(Left) As the opening picture of this article shows, the lack of a damping soldering paste causes the components to bounce, ruining the accuracy of both the position and the orientation of the components during the placing process.

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Overkill The spectacular images of crashing and bouncing components led to two conclusions. The first was that during the actual placing process the position of a component is temporarily overconstrained with regard to the number of degrees of freedom. Normally the movement of an object is determined by six degrees of freedom: Three translations along three axes at right angles with each other, and three rotations around those axes. As the component is placed, however, it is still attached to the stick or gripper, while at the same time touching the PCB surface. This means that additional degrees of freedom are imposed by both the gripper and the surface, which is too much. The overkill results in stress being built up between the gripper, the component, and the placing surface, so the componentâ&#x20AC;&#x2122;s state reverts to being undefined. In combination with the vibrations caused by the impact on placing, the forces imposed by the gripper and the placing surface dominate in an alternating fashion. The result is that the components bounce unpredictably all over the place and there goes your placing accuracy. Exceptional in simplicity The solution for dealing with the overconstrained state of the components was found by Ir Ronald Plak. As a mechanical engineer newly graduated from TU Delft he came to TNO in Eindhoven and found himself working on the MicroNed project. Plak came up with a passive system that releases degrees of freedom higher up in the gripper upon contact with the placing surface. â&#x20AC;&#x153;During the approach the gripper still rests on a collar, but as soon as an impact occurs, the gripper moves free, so the upper end of the gripper, which is attached to the rest of the machine structure by means of a membrane, is partially released from is restriction of movementâ&#x20AC;?, Puik explains. So as soon as degrees of freedom


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TNO researcher Ir Ronald Plak used a high-speed camera to find out if electronic components can be damaged by dropping them at high speeds.

are imposed by the substrate, they automatically become uncoupled within the gripper, resulting in a fully controlled and therefore accurate placement. “The system is exceptional in its simplicity”, is how Erik Puik describes Ronald Plak’s invention. Double spring, half strength The second conclusion from the impact research was that during the placing process the component can become crushed between the gripper and the surface. The impact force is a crucial factor, according to Plak. To prevent the component and the gripper from bouncing straight back due to the elasticity of the (depressed) printed circuit board, the gripper is fitted with a prestressed spring to force down the component. However, the result of the extra force is that the force of the impact is doubled. The story of Plak’s second invention is slightly more complicated, according to Puik. To solve the problem of the crushed components, he had to reduce the impact force. This force is caused by the deceleration as well as the build of the gripper, which contains the pressure spring already mentioned, which rests against a fixed collar. Plak investigated a whole range of complicated options, only to arrive at the simple concept of replacing the fixed gripper collar with a second spring. The result of this, he explains, is that as the gripper moves downward the extra downforce is still nil, to be slowly built up from the moment of impact. Puik: “The downforce starts by being very small, and then increases gradually. By fine-tuning the setup, you can actually halve the impact force.” This makes the placing process a lot more controlled and consequently, more accurate. Puik is enthusiastic about this solution as well: “Ronald added a second spring to the lower end of the first one. The addition of a spring costing, say 20 cents, has reduced the force acting on

This turned out not to be the case, with absolutely no reduction in quality being found even after multiple testing.

F r2

F gripper k

r1

w

Base structure

Contact point F impact

The theoretical method of calculating the Hertzian contact stresses

The test setup used for the experiments. On the left is a vertical

where the components meet the PCB surface can be used to show

slider used to simulate an accelerated pick & place machine. On

that a component will not damage itself in free fall. Any damage is

the right is the high-speed camera that records the process at

therefore caused by the component being mangled between the

16,000 frames per second. The test setup can reach approximately

suction device and the surface.

ten times the speed of a standard pick & place machine.

Guidance Drive unit Guidance Gripper

Contact Die & Nozzle = 6 Dof Constrained

Nozzle

Component Base

Rz a)

Z

Rz

Ry

X

Imperfections in the design of pick & place machines, lack of

Rx

Ry Y

X

Rx

Die

Substrate

the placing process. The anomalies result in the position of the component being overconstrained.

Z

Y

b)

parallelism in particular, can result in stresses building up during

Contact Die & Substrate = 6 Dof Constrained

Both the PCB surface and the suction holder try to impose their own position on the component. This battle of forces causes the positioning accuracy to be lost and can damage the component.

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Rz

Z Ry Y

X

Rx

Membrane Drive unit Gripper needle

The introduction of a smart design feature above

the component by half. You need to think in terms of energy to understand this. It was quite a stroke of genius.”

the suction device can prevent the placing process from becoming overconstrained and stressing the

Component Base structure

component. As a result the positioning accuracy is maintained and the risk of damage is reduced.

Eliminating the overconstrained state cannot prevent the component from bouncing around, as this is caused by the impact energy.

Drive unit

Drive unit

Pretensioned spring a)

b)

V drive unit, constant Pretensioned spring

Guidance

c)

Mgripper Gripper

By pushing the component into place by gravity or with the aid of a spring, the part is held down enough to prevent

a)

b)

Component

c)

v collision

Mgripper

d)

v collision

Gripper and component Stiffness of contact points

it bouncing. The drawback is that this

Patents The two smart solutions introduced by Ronald Plak, who has gone on to work as a mechanics system designer at CCM (Centre for Concepts in Mechatronics) in Nuenen, have been successfully tested in a simple device for a pick & place module. Further research was done in a follow-up project with Utrecht Academy, where Puik is professor of Microsystem Technology. Students did tests to measure the way the gripper caused printed circuit boards to flex and vibrate. Patent applications have been made for both of Plak’s inventions, in Europe as well as in the United States. All in all, the technology is ready to be brought to market and ready to be licensed. Negotiations have already been started with a number of interested parties, including a foreign company. According to Erik Puik, part of the success of this MicroNed project is due to the involvement in the feedback group of companies like Besi and Assembléon, which build placing machines and other equipment for the back-end of the semiconductor industry. “They were quite open in their collaboration”, Puik says, “and they shared their know-how. The people at Assembléon in particular were very frank about their state-of-the-art solutions. If they hadn’t been, we wouldn’t have got this far.” The external funding also played a major role. “Without MicroNed this couldn’t have taken off the way it did. It enabled us to properly tackle the problem. The outcome of the project, a solution for fast and accurate pick & place of fragile components, will be an essential ingredient for BlueBird.”

increases the force exerted on the component.

The addition of a second spring (C) to the lower end of the stick can prevent the component from bouncing while reducing the downforce to a fraction of that produced by the single-spring version (B) commonly used by the industry.

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BlueBird Ing. Roger Görtzen can confirm this. He also participated in the MicroNed project at TNO, and was closely involved in building the


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test setup. He then became involved in the main BlueBird project. As a founding father he managed to bring together a very diverse consortium, which in addition to TNO included such companies as ALSI, Assembléon, ASML, ASMI, Besi, EVG, ST and NXP, the three technical universities of Delft, Eindhoven and Twente, and the well known imec institute. This project is intended to provide answers to the challenges posed by the ever-continuing miniaturisation of ICs, with increasingly complex and expensive production equipment (such as the lithography systems produced by ASML) and the physical limits that are gradually looming on the horizon. An escape route within the existing footprint of microelectronics is to go upward by putting microchips on top of each other (3D stacking). For the time being the BlueBird project involves working on ways to modify the existing pick & place equipment for stacking fragile chips, Görtzen explains. “We learned a lot from the MicroNed project, and it definitely put TNO Science & Industry on the map as a major player that operates on the same level as the other partners in BlueBird. For example, it facilitated our introduction to what is probably the number one company in pick & place equipment for the chip-towafer-market, Datacon of Austria (part of Besi; Eds.). Within this project TNO is optimising the Datacon die-bonder to improve its accuracy from 10 microns to 2.5 microns while retaining its placing speed.” This is how the ambitious BlueBird initiative is destined to bring the Netherlands to the forefront of the back-end of the semiconductor industry – thanks to MicroNed.

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A dynamic (Adams) simulation of the final design to prevent bouncing. The figure shows the change in length of the spring and the increasing force as functions of the time. Plot number III represents the resulting contact force. The additional spring has resulted in a reduction of 50% relative to curve II.

The solutions to overcome the overconstrained state and the bouncing problem were both realised in a prototype and put through their paces at high speed in the test setup. The follow-up research is taking place at Utrecht Academy (Hogeschool Utrecht).

The final, patented, solution has remained relatively simple. The total For more information, please contact:

device contains fewer than ten parts.

Ing. Erik Puik, e-mail erik.puik@hu.nl or Ing. Roger Görtzen, e-mail roger.gortzen@tno.nl.

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Production rates for microchips and microcomponents for MEMS are high, with manufacture often taking place in batches on wafers containing hundreds to even thousands of identical components. The lithography machines built by ASML for example, are designed not only to work with breathtaking accuracy, but also to cope with dizzying throughput. However, once the separate components are ready, the process sometimes stalls because for assembly into a microsystem means bringing them together very accurately piece by piece. At that point, the pick & place equipment sets the pace, and the entire production process slows down a gear. This bottleneck in the microsystem production process prompted several researchers to search for fast alternatives while maintaining the required accuracy. At TU Delft, selfassembly has been brought in to let the component do the Silicon-based manufacturing techniques make it possible to produce large numbers of small components in batches. The subsequent assembly of these small components is a serial process. Assembly is usually

work themselves.

Image: Philip Broos

done by pick & place equipment. Higher production rates can be achieved by using more machines, but this does not reduce the cost per placed component. Self-assembly, or autonomous assembly, is a promising solution; can large numbers of components be arranged with a minimum of effort per component?

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By Hans van Eerden


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Self-assembly for microsystems: faster, cheaper, smaller DIY at Delft University of Technology Fast and accurate positioning of components is exactly the type of challenge that appeals to the Precision and Microsystems Engineering (PME) department at the Faculty of Mechanical, Maritime and Material Engineering of TU Delft. Within the department, the Micro and Nano Engineering Laboratory, led by Professor Urs Staufer, has shifted the focus of its production technology research from classic mechanical engineering production techniques towards small-scale components and extreme precision. So micro-assembly and nano-assembly are now on the menu in Delft, according to Dr Ir Marcel Tichem. The primary interests of the group, with its mechanical engineering roots, don’t lie with the construction of a few prototype demonstrators, but in the development of functionally complete systems that can be manufactured in an industrial process. Ice gripper Micro-assembly research at TU Delft focuses on new concepts. One research project concerned a so-called ice gripper, a device that can pick up components by rapidly freezing onto them and then heating up quickly to drop them in another spot. Another surprisingly ingenious and assembly-related concept was developed as part of the research into the sub micrometer-scale alignment of glass fibres using a MEMS (Micro Electro Mechanical System). In a follow-up project, researchers are currently working on the alignment of optical microchips with an accuracy of 0.1 micrometres. When MicroNed came in, the university submitted the subject of new assembly concepts for the Micro Factory cluster. This resulted in the Micro Assembly work package with Tichem as coordinator. Iwan Kurniawan went to work on self-assembly under Tichem’s supervision. Kurniawan, a Bachelor of Mechanical Engineering from the famous ITB in Bandung, Indonesia, had already participated in the ice gripper research for his master’s course at TU Delft. In 2005 he started his doctorate research in a MicroNed project, batch assembly of hybrid microsystems, which aims to find an alternative to the conventional pick & place devices used in the assembly process.

Concepts for micro-assembly Various concepts for micro-assembly exist, Tichem starts his explanation. The pick & place machines already mentioned provide an obvious solution, but that doesn’t mean they will always work trouble-free. The problems that always occur when accurately placing components are highlighted in another article in this publication, with components that bounce all over the place, and ingenious solutions to suppress their behaviour. This research was part of a TNO research project (in the same MicroNed work package) investigating the placing of components onto a printed circuit board. Another option for assembly is to use what are known as product-internal assembly functions, Tichem continues, in other words, assembly functions that are built into the product itself. One example is the above-mentioned instrument for aligning glass fibres that his group developed. And there are no doubt many more smart methods, each with its own bag of tricks for assembling certain components. However, the search was on for a rather more generic method, and that is when Kurniawan had the idea of forgetting about a smart assembly device, and instead have Mother Nature (or rather, the components) do the work. In other words: self-assembly. Pitch The initial concept was that of having two different components of a microsystem, each produced on a wafer of its own, and with the microchips on both wafers having the same dimensions and pitch (the fixed distance between the identical components on a wafer). You could then simply stack one wafer on top of the other (wafer-to-wafer bonding) to assemble the components, which could then be cut free from the stacked wafer. For practical applications the concept turned out to be a bit too optimistic. For one thing, the pitches of both wafers certainly don’t always match. However, the idea had laid basis for a practical concept, because if you cut one of the two wafers into separate components, you can then arrange those on an alignment carrier (a wafer with

Adhesive rim

BAW-filter chip

Cap 950 x 500 µm

300 µm Cap 950 x 500 µm

380 µm Cap 950 x 500 µm

A MEMS wafer contains chips with structures that need to be able to move. Such structures could act as a (mechanical) filter, for example. In addition, the wafer carries integrated electronics. To protect the mechanical part, a cap is placed over it, leaving the electronics section accessible for the application of electrical connections.

Cap, 250 µm thick

BAW-filter wafer

Adhesive rim

Sectional view of a MEMS chip with a protective cap placed on a thin adhesive rim that hermetically seals the fragile MEMS structure.

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special features to enable components to be aligned) to match the pitch of the other, still uncut, wafer. With the components on both wafers now matched in pitch, hundreds to thousands of devices can be assembled in a single operation.

Pre-alignment on intermediate carrier

Concept of the self-assembly method researched in Delft. Having been cut from the wafer, the chips are removed from the self-adhesive membrane (known as dicing tape) for assembly and then distributed at high speed and low accuracy on an alignment carrier. The autonomous alignment of the chips takes place on the carrier, after which they are arranged on the carrier in an accurate and regular pattern. Then the chips are transferred in one operation (in one batch) to the wafer on which they are to be assembled.

In a typical pick & place

If the chip is incorrectly oriented

procedure a chip is pushed from

for assembly, a rotation unit

below to release it from the cut

turns it around (known as chip

wafer, which is stuck to the blue

flipping).

dicing tape, to be picked up from above by a vacuum picker.

Example of a pick & place machine as used in the electronics industry for the assembly of MEMS and semiconductors. Doctoral student Iwan Kurniawan used this machine at the Austrian Datacon company for a number of his experiments.

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The chip is then picked up by a

In the last step the chip is finally

second vacuum picker.

placed on the substrate.

Electrostatic The main challenge is to align the separate components on the alignment carrier very efficiently and accurately enough to ensure that they fit perfectly onto the matching components in the uncut wafer. This was the challenge facing Iwan Kurniawan in 2005. His idea was to use electrostatic forces. As an alignment wafer he used a silicon wafer onto which a pattern of electrically chargeable patches had been applied. The components were then expected to position themselves along these patches. The patch material is silicon dioxide (SiO2), a material that can be electrically charged and then retain its charge. Under the influence of the charge, components positioned above the surface will start to become polarised, as a result of which the components and the surface will attract each other. If the alignment carrier for example is positively charged, polarisation will cause the part of the microchip nearest the alignment carrier to become negatively charged, with the part furthest away from the carrier becoming positively charged. The overall charge of the component remains nil, but since the electrostatic attraction (and vice versa, repulsion) between two objects depends on the distance between them (smaller distance means bigger force), the +/â&#x2C6;&#x2019; attraction will outweigh the +/+ repulsion. The net result will be attraction. The alignment carrier and the chips could also be charged with opposite charges to increase the attraction forces even more. The places were no chips are to settle are covered with a layer of aluminium, which is subsequently grounded, so that it does not retain any charge and will therefore not affect the components. In this way, the wafer will become covered in a chessboard pattern of charged SiO2 fields separated by uncharged Al fields. Components are then loosely deposited on the charged wafer, which is then vibrated. The components will start to move about, until they get trapped by one of the electrostatic fields, holding them in the required position. Second-hand laser printer Iwan Kurniawan decided to work out the details of his idea. On


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the internet he bought a second-hand laser printer from which he salvaged the electrostatic charging unit. In a laser printer, this unit charges a rotating drum in a pattern matching the image to be printed; the electrostatic charge attracts the toner, and the rotating drum transfers the toner pattern onto the paper. Kurniawan used it to make a device that used a so-called corona discharge to charge the alignment carrier (and the components, if required) in a kind of spray-charging process. Once he had demonstrated the feasibility of the principle, he went on to build a more professional corona device. He then constructed a setup that could vibrate an alignment carrier onto which components had been scattered. He had the alignment carrier with the required pattern, initially for 5 × 5 components, made at DIMES, the Delft Institute for Microsystems and Nanoelectronics. Experiments with the first silicon alignment carrier, which used only

Naive Just run the experiments and the proof of concept would be in the bag, that is what Kurniawan thought: “Initially I was naive enough to think that electrostatics would do the job.” Alas, no such luck. Although the components ended up in roughly the right locations, the required accuracy was nowhere to be seen. With hindsight it was clear that the cause lay in the shape of the electric field just above the charged carrier. In the vertical direction, perpendicular to the surface, the attractive force is strong – you can hold the carrier upside down without losing the components – but in the horizontal direction the field gradient is only slight. The result is that the components – like magnets on a planning board – will not move into their exact target positions.

electrostatic charging.

For his experiments Kurniawan constructed a charging unit that used a corona wire to apply an electrostatic charge to the SiO2 patches on the alignment carrier.

Working principle:

Detail of the second alignment carrier. Kurniawan has applied a

Legs Kurniawan’s solution for the required fine-tuning of the positioning was redefined in geometrical terms, with a dummy chip that – fitted with a leg at each corner – would fit perfectly into a certain shape on the alignment carrier. Therefore a new alignment carrier had to be made, this time with holes corresponding to the legs on the chips. Experiments showed that this solution worked much better – electrostatically attracted, the chips clicked straight into their exact positions – but that was where symmetry presented itself as the next obstacle. Although an externally symmetrical component may end up in the correct spot, it’s not automatically pointing in the right direction. So, both the

pattern of slots in each position where a chip is to be aligned. The chips have been fitted with legs that fit the slots exactly. At the centre of this pattern is a thin layer of silicon dioxide (SiO₂) to which an electrostatic charge has been applied. The alignment carrier is not the only object featuring a thin layer of SiO2. So does the chip. The geometrical properties (legs on the chips, spaces on the carrier) are complementary and match each other perfectly. The SiO2 patterns are given opposite charges so the chips are attracted to their optimised position on the alignment carrier. The geometry then ensures that the chip can only be accurately aligned on the wafer in one way.

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Chip2Foil

An important prerequisite for self-aligning micro-components by means of electrostatic fields is that the chips are stirred into movement relative to the alignment carrier. Otherwise the chips will stick to the surface of the alignment carrier. The Delft researchers used a simple vibrating table to move the carrier up and down.

The European Union for one sees a future for the concept. A grant was awarded to Chip2Foil last year, as part of the Seventh Framework Programme (www.chip2foil.eu). The project is about the application of UTCs (ultra-thin chips) on foil for the production of microsensors. The applications include systems for drug metering, known as smart blisters, and smart packaging that could for example indicate the freshness of packaged food. Dr Ir Tichem is the coordinator of this European project. He considers the grant from Brussels a result of the self-assembly research. Self-assembly appears to be eminently suited to extremely small components. In this project self-assembly is used to rapidly position ultra thin chips relative to on-foil circuits, after which the electrical connections are printed between them. The partners in the project are the Holst Centre (electrical interconnections), IMEC (for the UTCs and reliability), DSM (foil and the applications), Datacon (for the chip handling), Orbotech (for optical inspection) and Plastic Electronic (for the mechanical chip-bonding). All in all, the Delft group has its research partners lined up. Now if only those elusive components would do the same...

Detail view of a wafer and chips showing the SiO2 surface and the four symmetrically placed alignment legs. The Smart Blister is an application in which large numbers of very thin microchips are placed on a foil, preferably using a reel-to-reel production method. As part of the Chip2Foil project at PME (funded by the EU Snapshots of various moments during the alignment process using

7th Framework Programme), TU Delft is looking for ways in which self-

chips with symmetrically located legs. The 16 chips are aligned in

assembly can play a role to enable high-volume and low-cost execution of

about 15 seconds. The alignment time is independent of the batch

this process. See www.chip2foil.eu.

size.

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alignment carrier and the microchip had to be given an asymmetrical pattern. On the carrier the pattern consists of holes, and on the chips a pattern of legs ensures alignment. Off to DIMES Kurniawan went again, to get a new carrier. It all turned out to be worth the trouble, because he was able to carry out a number of rewarding experiments. Video images show dancing components that all – sooner or later, due to the random nature of the process – find the right positions of their own accord. Feasibility In Kurniawan’s setup the components, say silicon caps placed as protection over an electronic circuit on a wafer, are not only polarised (by the charged wafer surface) and in some cases even electrically charged, but they also dance all over the place. What does this rough treatment mean in terms of practical feasibility? “Mechanically I cannot see any problems, but on the electricity side, polarisation or charging could certainly cause damage. My method will not be suitable for electronic chips, but it could be used for optical or mechanical components”, Kurniawan says. As it is, the researchers from TU Delft have already been working on an alternative for the electrostatic positioning force. Since the alternative concept is the subject of a patent application, their lips must remain sealed for the time being. And speaking of financial feasibility, in some cases a chip still needs to be modified, i.e. fitted with legs, to achieve accurate positioning. It all comes at a cost, Kurniawan concedes, but self-assembly does obviate the need for pick & place equipment and speeds up the production process, which is why he expects it to be profitable. “By the way”, Kurniawan says, “we have also designed a configuration giving only a geometrical pattern to the alignment carrier , and requiring no modification of the chips.”

Part of a cut wafer showing asymmetrical microchips.

Close-up view of an alternative design for the alignment carrier, in which certain locations on the carrier have selectively been given many legs, leaving room elsewhere on the alignment carrier in the locations where the chips are to be positioned. The chips are not electrostatically charged. In this case the chips require no geometrical features; the vibrations will automatically deposit the chips in the holes, removing a major drawback of the earlier design. In this new design there is no need to modify the chips, just the alignment carrier.

To allow for one possible position only, an asymmetric pattern of

Follow-up A first spin-off from Iwan Kurniawan’s research was a followup project that received funding in 2009 from the MEMSLand programme of Point-One. He applied his concept to an actual production stage, the positioning of protective caps on a waferfull of MEMS-chips. The wafer with the chips and the alignment carrier were made available by the NXP company, and the experiments were conducted at Datacon Technology in Austria, where a component placing machine was used for prepositioning. The

cavities and pedestals on the chip was designed.

Close-up view of legs around the free space (the SiO2-surface) on the alignment carrier.

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The same alignment concept has been applied to an industrial case, placing protective caps on a MEMS Snapshots of the alignment process using the second carrier design,

wafer. The snapshots of the

with no protrusions on the chips. The 25 chips took about 15 seconds

alignment process show how

to be aligned.

40 caps are aligned in about

chips used were smaller than the model systems used in Delft and this produced difficulties of its own. “Due to the ever-present electrostatic charge, the chips wouldn’t come unstuck again once they had been picked up by the vacuum picker, because the effect of gravity was too low for their slight weight. Using air to blow them loose didn’t work either since this blew previously placed chips away as well”, Kurniawan recalls. This was a first for Datacon, because their equipment always places components on soldering paste or adhesive. Kurniawan: “In the first experiments, by placing the chips further apart, we managed to align 240 components to produce a yield of far above 80 percent, even over 95 percent. But in practice it still remained quite a challenge.” Another spin-off effect of the research project concerned the TU Delft curriculum. Students contributed their bit to the design of the alignment carrier, to the construction of the corona discharge device, and to measuring the applied charge. Tichem used the knowledge and the experience gained from the self-assembly projects as teaching material in his lectures. “Hopefully, up-andcoming young professionals will help to introduce these new techniques in the industry.”

5 seconds. The caps measure about 500 × 900 μm.

Conclusion Five years have now passed since the MicroNed project started. The researchers have demonstrated great examples of selfassembly, but they have also experienced how unruly the subject matter can be. They are sharing their experiences with fellow researchers in countries like Belgium (IMEC at Leuven/Louvain) and Finland, who are battling with similar concepts. Tichem and Kurniawan are convinced their approach has a future. Tichem: “In practical terms, one of the feasible implementations in the short term is to combine pick & place with self-assembly.” Pick & place would then be used to bring components quickly, though inaccurately, into the desired position, after which selfassembly would take over to apply the finishing touches in the form of accurate alignment. For more information please contact: Dr Ir Marcel Tichem, e-mail m.tichem@tudelft.nl, or Iwan Kurniawan M.Sc, i.kurniawan@hotmail.com.

Close-up view of the MEMS wafer onto which the caps were to be assembled at Datacon.

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One of the projects at PME involved designing an ice gripper, which was built in collaboration with Integrated Mechanisation Solutions (IMS). In a flash, a component is frozen to the gripper using a droplet of water, picked up, and moved. After rapid heating, the connection melts again.

Wafer and chips, the protective caps that are to be placed onto the MEMS on the wafer above.

Microscopic view of the area on the Datacom MEMS wafer over which the protective cap was to be placed.

In another project, financed by IOP Precision Technology, a chip with

Microscopic image of the alignment carrier used for the test at

MEMS structures is used to position and fix in place an optic glass fibre,

Datacon. The upper image shows the still empty socket. Below it

using two degrees of freedom to achieve sub-micron precision. This

the socket contains the aligned protective cap. The amount of play

design has been patented.

between the cap and the socket determines the maximum achievable alignment accuracy.

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Part 3

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MST in space

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Delft University of Technology has been in the public eye for many years with its programme for building and launching small or nano satellites. The MISAT cluster – part of the MicroNed programme – has given this development a major impetus. Not only has the university conceived plans to develop a satellite colony in space that can serve as a radio telescope, but the project has already generated a major spin-off. And there’s more where this is coming from, with a decade’s worth of questions waiting for graduate and doctoral students to get their teeth into. As the breeding ground of MISAT, MicroNed has put nano-scale Dutch space research on the map. Artist’s impression of a future OLFAR mission, with a swarm of microsatellites in a lunar orbit. While the satellites are passing behind the Moon, they will be able to detect and record very weak radio signals from distant galaxies without interference from terrestrial signals. When the microsatellites emerge from behind the Moon after about two hours, the recorded data is relayed to the earth station. This generation of microsatellites will simply be put into an Earth orbit from which they will navigate to the Moon under their own power.

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By Ruud Overdijk


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A satellite swarm as radio telescope Ant colony It was a television broadcast by Dutch TV network VPRO that led to the insight that small, limited-intelligence satellites can also be used to achieve great results. “In 2004 we were watching a programme about an ant colony”, Verhoeven recalls, “which showed how ants in numbers can work together to do all kinds of useful things without being aware of it. This gave us the idea of developing a satellite colony in which numbers of satellites work together. The animal kingdom has many examples of small animals that aren’t very intelligent, yet manage to achieve quite a lot. Ants, like bees, live in colonies and work closely together. If you see nanosatellites as insects, you need to look at the insect world for ideas on how they would behave Insects operate most effectively when they are in a swarm, so nanosatellites could also complete a mission success­fully by operating in a swarm.” This insight also gave us a clue to the kind of mission for which nanosatellites would be best suited. Verhoeven: “You don’t need lots of satellites for every mission, and if you don’t need lots of satellites, there’s no point in using a swarm. In my opinion one of the main breakthroughs of the MISAT programme is that we have discovered that nanosatellites should be compared with insects, and that they should operate in swarms. This realisation enables us to move in a whole new direction of space research.” Space telescope Thinking about the type of mission suitable for a swarm of nanosatellites, Verhoeven hit on radio astronomy. The Netherlands has made major contributions to the field with the radio telescope at Dwingeloo (dating from 1956) and the Westerbork Synthesis Radio Telescope (which entered service in 1970). The latest development is the LOFAR (LOw Frequency ARray), which entered service in June of this year. Radio astronomy is about detecting radio signals originating

The spare flight model of the Delfi-C3 satellite, which has been steadily orbiting the Earth for well over two years now. The ground station at TU Delft as well as radio hams all over the world make radio contact with the microsatellite several times a day.

Microsatellites and nanosatellites are small and light, which is why it should be possible to launch them using specially modified guided missiles fired from jet fighters in flight. This would avoid the need for expensive launch vehicles

(Photo: internet)

The space research activities at TU Delft really stemmed from a desire to do something different for a change, says Dr Chris Verhoeven of the faculty of Electrical Engineering, Mathematics and Computer Science. “Electronics and spacecraft form an interesting combination. A few years ago we decided to build a small satellite the size of a brick and weighing a few kilos, known as a cubesat. The result was Delfi-C3, the first Dutch university satellite, which was built in collaboration with the faculty of Aerospace Engineering.” Delfi-C3 is called a microsatellite, but it is in fact a nanosatellite. According to the official definition a microsatellite weighs between 10 and 100 kg, while a nanosatellite weighs between 1 and 10 kg. Delfi-C3, which weighs a bit over 2 kg, was launched in April 2008 and it is still orbiting the Earth in good order. The adventure didn’t end with that first satellite however. Researchers wanted more, and so started to think about options for the next steps. As far back as 2003 there had been ideas of working with a whole colony of small satellites rather than a single spacecraft (see ‘Microsatellite swarm reduces vulnerability’ in Delft Outlook 2004-1). A colony of nanosatellites would be less vulnerable than a single standard satellite, in terms of gamma radiation and solar storms as well as cost cutting. Small and light, nanosatellites could be mass-produced in the future. Given the average launch cost of about € 50,000 per kilogramme, nano­satellites provide such a low-cost approach to space research that even the Netherlands can afford. However, the compact nature of the satellites also presents a problem. Equipment inside the satellite runs on electric power and produces heat that is difficult to dissipate in the vacuum of space. This limits the capability of small satellites, since we cannot keep making them smarter simply by adding more processing power. In other words, although nanosatellites are nice and small, they are also limited in their on-board intelligence.

launched from Earth. It would also require less energy to get them into orbit, since the atmosphere is much less dense at higher altitudes. Using this method a nanosatellite could be launched exactly when it is required (e.g. in the event of a natural disaster) and then become operational within 3 to 4 hours.

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Artist’s impression of the Delfi-n3Xt satellite. The successor to Delfi-C3, it will be launched by conventional means in 2011. It is currently being developed and built by the project partners: TU Delft, ISIS, TNO, SystematIC, NLR, Dutch Space, and MicroNed. The new features that distinguish it from Delfi-C3 include a fully capable on-board attitude (Image: TU Delft)

control system, a microthruster (still experimental), new solar cells (a test model), and an S-band transmitter for high data transmission rates.

The behaviour of a swarm of nanosatellites will have to be achieved by applying only a few simple rules, just like in the natural world. Take a flock of birds, for instance. Each bird knows it should avoid flying into its neighbours as well as any obstacles. When a flock flies around a church steeple, the entire flock swerves, and it does it in such a way that the average energy expended by the birds is kept to a minimum. As far as is known, the birds do not communicate about the process, but manage to avoid the obstacle purely by applying the simple rules: ‘avoid collisions’ and ‘waste as little energy as possible’. Biologists call this emergent behaviour.

Microsatellites or nanosatellites in swarm formations will excel in exactly those fields in which standard satellites find it hard or impossible to operate, e.g. in ultra-low orbits, unstable orbits, and in deep space (e.g. in asteroid and radiation belts), any trajectory in fact that is expected to curtail the service life of the spacecraft. Swarms can be used to monitor certain areas much more frequently and from a variety of angles simultaneously. Microsatellites and nanosatellites can also operate in extremely low Earth orbits (100 – 150 km), enabling them to come closer to their observation targets. However,

from outer space and analysing them to find out how the universe was created. The universe has been expanding ever since the Big Bang, but we can still pick up signals from its early beginnings. Several satellites have been launched that are providing us with highly detailed images of that period in time. There is however a certain period right after the Big Bang from which we can detect very little. We do know that there should be radio signals produced by hydrogen, but due to the expanding universe and the long time it has taken those signals to reach us, their frequency is lowered, a phenomenon known as red shift. The Earth’s atmosphere prevents us from detecting any signals below 10 MHz using earthbound systems. To detect such signals in space, you need a space telescope with a very large area. Observations from space are also plagued by another problem, which is that the Earth is a massive source of interference. Observations by NASA’s Explorer missions in the early 1970s showed that the problem can be solved by moving out of sight, beyond the Moon. So hence the idea of creating OLFAR (Orbiting Low Frequency ARray) in the ideal location for a large space telescope on the far side of the Moon. “OLFAR consists of a swarm of nanosatellites covering an area of 100 square kilometres”, Verhoeven explains. “Together they form a large telescope array that we can use to detect low-frequency signals between 100 kHz and 30 MHz. This not only enables us to look at the period right after the Big Bang known as the Dark Ages, but also to search for earth-like planets outside our solar system. In addition we might be able to detect traces of highenergy particles in the universe as they strike the Moon. We can do many different things with an instrument like that out in space.”

the relatively high drag induced by the upper atmosphere will limit the service life of satellites in these orbits to between ten to eighty days, depending on the solar cycle, but this doesn’t really matter since a swarm element is in fact expendable.

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Plasma motor So the idea of a swarm satellites had been born, and with it the concept of a possible mission. Knowing where to send your sat-


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While Delft-n3Xt will soon be flying with a microthruster based on

(SEM-Photo: Courtesy of H. Shea, EPFL, http://lmts.epfl.ch)

cool-gas generators (see MicroMegazine 3), CubeSats will use ion motors. This is a SEM image of a single ion generator (70 μm high with an inner diameter of 20 μm), 19 of which together in an array form the electric motor. The array was designed and manufactured from pure silicon using etching techniques by Ir R. Krpoun and Dr H. Shea of the Microsystems for Space Technologies Laboratory at the École Polytechnique Féd. de Lausanne. The silicon balls in the capillary tube regulate the hydraulic impedance.

(Image: Steven Engelen / TU Delft)

ellite swarm is one thing, but actually getting it there is another thing altogether. Verhoeven: “Inspired by the insects we came up with the idea that they should be able to fly there autonomously. This can be done using a small plasma motor that ejects high-velocity ions. A motor like that produces very little thrust, but it can do so for very long periods. It could remain active long enough to get the satellite near the Moon in a year.” Self-propelled satellites turn out to offer other benefits too. First of all it enables the telescope to be built one satellite at a time, so you don’t need a large and expensive system to deliver 50 satellites to their calculated destination. The second benefit is that the satellites become much more flexible once they can fly by themselves, widening the range of applications. For example, you could have a few carrying a cheap optical instrument stationed 400 km above the Earth, and if you needed to observe a place on Earth, e.g. in the event of a natural disaster, you could simply direct them to the right spot.

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An artist’s impression of a future OLFAR nanosatellite with its 5-m long dipole antenna to receive radio signals from distant galaxies. The solar panels provide power for, among other things, the ion motors that will move the satellite from its Earth orbit to its destination in an orbit around the Moon. Radio telescopes like the large dish arrays at Westerbork, scan the heavens for higher frequencies that limit the amount of time we can look back into the past of our universe. In addition they can be used to investigate highfrequency phenomena such as radio pulsars, galaxies, hot gas clouds, quasars, magnetars, and gamma ray bursts (as long as they extinguished long enough ago).

(Photo: Astron, Dwingeloo)

Pulsar navigation system If a satellite flies autonomously, it also needs to know where it is. In comes the second major addition, an on-board navigation system. “We have found a very exotic solution for this”, Verhoeven says, “in the form of a pulsar navigation system. Pulsars are rotating stars that emit a highly stable wide-band radio signal. Some 1800 potentially usable ones have now been identified, each with its own signature, and they make for very good timers. They are a bit like electromagnetic lighthouses you can use to navigate by.” Various graduate students have already demonstrated that pulsars can be used for navigation purposes. Building the receivers and the navigation equipment will take a few years yet, but once

The new LOFAR radio telescope scans for much lower frequencies (approx. 10 – 240 MHz), which is why it covers a much larger area than the dish radio telescopes. The small telescopes are linked up to form a single giant virtual instrument using interferometric methods.

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complete it will provide a good navigation system that can also be used here on Earth, and, depending on the required accuracy, will at least provide a reliable backup system for the current GPS. Unlike GPS it doesn’t require a bunch of satellites to be kept in permanent orbit, and nobody can switch it off or jam it.

In 1968 NASA launched the Radio Astronomy Explorer 1, the first lowfrequency space-based radio telescope, to study the background radiation. It immediately detected that the Earth’s ionosphere itself emits a whole range of signals, a major discovery that came as a complete surprise. It was impossible to determine where the radio (Image: TU Delft)

signals were coming from, so no image could be made. In June 1973 NASA launched the RAE-2 into a Moon orbit. Its readings proved that the far side of the Moon is completely shielded from terrestrial interference and that this made it possible to perform low-frequency research from there. The satellite’s lack of a directional antenna meant that relatively little information could be gathered.

An OLFAR telescope will consist of several dozen nanosatellites, offering many antennas that can listen for radio signals in the

Roaming Once nanosatellites can fly themselves and be aware of their position, the sky is the limit”, an enthusiastic Verhoeven says. “You could send them to the Moon, or even beyond to investigate planets. Or you could just allow them to roam and wait until they find something worthwhile. They could for example find an Earth-skimmer, attach themselves to it, and use their pulsar navigation system to keep us updated about its position. Or they could be used to find space junk, latch onto it, and then gradually push it towards the Earth until it burns up in the atmosphere. In this way they would be working just like antibodies cleaning up space. If space junk really starts to become an issue, launch providers could demand that 20 or so space antibodies be taken along with every launch.”

low-frequency range spread out in their lunar orbit. While the nanosatellites are hidden behind the Moon, they store the information about the received radio signals and pass it on to the other satellites to correlate the data. The volume of the preprocessed data will be much less than that of the individual data from each satellite, making it much easier to relay back to Earth via the satellite that is closest to us at the time. This makes for a considerable reduction in the bandwidth requirements of the transmitter and the energy it would take to send the data, the distance between the Earth and the Moon being very large. This is just one of the possible scenarios. An alternative would be to have each of the satellites store its own collected data and then send it back to the earth station using its own systems.

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OLFAR is an ambitious plan for which a lot still needs to be done. Verhoeven: “We need to work on the satellite’s propulsion, navigation and attitude control systems, but also on sufficient memory capacity, long-range radio, etc. We intend to develop all these technologies bit by bit, and test them on separate nanosatellites. We have the ambition to do this within the next ten years. Before this decade is out, the Netherlands could and should have sent a nanosatellite to the Moon. OLFAR has become the magnetic North of our compass.”


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Pulsars are neutron stars that revolve around their axis at high speeds, emitting extremely powerful electromagnetic radiation. Like a lighthouse, the star sweeps its rotating radiation beams past the Earth at regular intervals. Each pulsar has its own extremely stable rotation rate, on a par with most atomic clocks, making the pulses eminently suitable as time references. As we also know the exact position in the sky of each pulsar, electrical engineers at TU Delft decided to design a special pulsar-navigation receiver for use aboard nanosatellites,

Spin-off OLFAR could prove to be a major stimulus to Dutch space research. It is also a project that attracts numerous graduate and doctorate students, and that could generate important spin-offs. Innovative Solutions In Space (ISIS) for example, is a company that evolved directly from the space research activities at TU Delft and which is also involved in MISAT. “ISIS is a direct spin-off from Delfi-C3”, says Jeroen Rotteveel, one of the company directors. “The company was founded in January 2006 by five people from the project management team, and today it employs 29.” The core competence of ISIS is Space Systems Engineering, i.e. supplying products and services to support spaceflight projects. The focus is on microsatellites and nanosatellites. ISIS supplies products such as radio transmitters and receivers, antennas, earth stations, sensors, and complete satellites (CubeSats). Some of the products were developed in house – and in some cases were a spin-off from research conducted at TU Delft – while other products come from outside suppliers. Customers are free to choose the package of satellite parts and subsystems they want to purchase, and ISIS provides the support for the entire package.

enabling the satellite to determine its position, velocity, and acceleration regardless of their position in the solar system. It will no longer be necessary to carry an atomic clock, since the pulsar signals are just as accurate. This offers great advantages to spacecraft designed to travel far into deep space and which have to be as light as possible, with the lowest possible power consumption. In the course of his doctoral research, Dr Chris Verhoeven invented a new type of oscillator for which a patent was granted. Both transmitters and receivers use oscillators. Verhoeven’s design is remarkable for one thing because of its extreme stability. It also contains very few components,

ƒresonator

which improves its robustness. When Ir Wouter Weggelaar became involved in the Delfi-C3 project as part of his graduation work, he designed a transceiver based on this oscillator.

ƒfosc

Transmitter side of the transceiver designed specifically for the Delfi-C3 satellite by Ir Weggelaar, which now contacts the TU Delft earth station

Transceiver “We see our role in space technology mainly as that of systems integrator”, Rotteveel says. “We collect separate technologies and equipment and stick them together so they become useful. That’s also how we see our role within MicroNed. Everybody was working on the latest technologies, but the glue that holds everything together to form something socially and commercially relevant seemed to be somewhat lacking. We convert MicroNed’s results into a commercially viable product, which we then market together. That is the great challenge offered by

from space on a daily basis. The spacecraft carries two transceivers, because a satellite’s communication system is crucial for achieving its mission objectives. The transceivers contain extra circuits to enable them to also operate simultaneously as transponders to relay incoming signals directly without the intervention of the onboard computer. The linear transponders operate in the amateur radio bands (downlink: 145.870 MHz / 2-m band – uplink: 435.550 MHz / 70-cm band). The range of the 100 mW transceiver is 650 km (overhead) to 3000 km (with the satellite on the horizon). Radio amateurs all over the world have been using the Delfi-C3 relay facilities with great success for the past two years.

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Using the knowledge gained from the Delfi-C3 project, ISIS has designed its own transceiver. The system architecture has remained largely the same, but a number of modifications have been made, one of which was to omit a conversion step for the transponder, which was a mission objective specific to Delfi-C3. The transceiver still operates in the amateur bands. Other modifications include the variable data transmission speeds for earth station links. The current ISIS transceivers have been fitted with a 104-pin connector, which has become a de facto standard in CubeSats. The prototypes were tested in thermal chambers for heat resistance and in vacuum conditions, as well as on vibration tables to simulate launch conditions.

a project like MicroNed: implementing new technology at the right moment to create a good product.” The transceiver mounted in the Delfi-C3 satellite is a fine example of the way in which technology developed at TU Delft can continue into industry. The device contained a new and innovative type of oscillator developed from a concept by Verhoeven. Wouter Weggelaar, who now works at ISIS as an engineer, worked on the device for Verhoeven during his graduation year. “The transceiver worked perfectly – and still does”, says Weggelaar, “but it was purpose-designed for Delfi-C3.” With a number of modifications, some minor, some major, ISIS managed to convert the transceiver into a universal transceiver product for CubeSats. Weggelaar: “For example, we replaced the connector that links it to the other electronics inside the satellite with a type that is the de-facto standard for commercially available CubeSat products, and we changed the power supply section to match what you would expect to find in a standard CubeSat. We also developed an entirely new software package. The data transmission rate has been increased and made adjustable, and it now has user-selectable modulation types for uploading data to the satellite. This product is now selling well.”

The engineers at ISIS also designed a modular antenna system that offers optimal performance in combination with the ISIS transceivers. The system combines the mechanical, electrical, and data transmission interfaces of the antenna in a highly compact system that can be mounted on top of a small satellite. It contains four coiled antennas made of special memory metal, and each antenna element can be individually deployed.

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Cost-effective ISIS has a large number of customers all over the world, including many academic research groups. “Less than one million euros will buy you a nanosatellite mission”, Rotteveel says. “That is in an entirely different league from the 3,500 million euros it cost to send Galileo into space. A million euros is a budget available to a research group for pioneering research, and so that is where most of our customers can be found. Then there is growing interest from government organi-


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The ISIS S band transmitter for nanosatellites is the latest addition to the product range. Compared with its predecessor this transmitter uses a much higher frequency range (2.3 – 2.5 GHz), making much higher data transmission rates possible. With missions carrying complex payloads such

sations and organisations such as ESA and NASA, because small satellites can be used to fly very cost-effective missions.” In addition to the systems engineering branch, ISIS has two subsidiaries: Innovative Data Services (IDS) and Innovative Space Logistics (ISL). ISD supplies data to customers. The data can come purely from satellites, or it can be enhanced by data obtained from entirely different systems. IDS can collect the data, process it, and deliver it in a customer-specified format. ISL is the company’s launching services, which acts as a broker for small satellite launches. “We handle all the interfaces”, Weggelaar explains, “both on the technical side and the organisation side. We have a lot of know-how, and we know the launch providers, which enables us to do business quickly and efficiently.” For a company like ISIS the knowledge of the MicroNed participants is essential if it is to bring new and innovative products to market. And for programmes such as MicroNed, companies like ISIS are of major importance for translating the scientific and technological developments into systems that are valuable to society as a whole. This makes MISAT a prime example of how all parties can profit from collaboration.

a system will be essential to ensure that the nanosatellites can send their scientific data back down to Earth.

Standard ISIS casing for nanosatellites. This modular system, combined with other products from the ISIS portfolio, forms the basis for a range of satellites ISIS is developing for its own use and for customers. ISIS also operates as a systems integrating partner for nanosatellites, and the company currently has contracts for five satellites.

For more information, please contact Dr Chris Verhoeven, phone +31 15 278 6482, e-mail c.j.m.verhoeven@tudelft.nl, or Ir. Erik-Jan van Kampen, phone +31 15 278 7147, e-mail e.vankampen@tudelft.nl, or Ir. Jeroen Rotteveel, phone +31 15 256 9018, e-mail j.rotteveel@isispace.nl, or Dr Bert Monna, phone +31 15 251 1100, e-mail b.monna@systematic.nl.

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Interval analysis has many practical uses Interval analysis is a mathematical technique that instead of singular or crisp values uses an interval of possible values. As an example, let us assume that a satellite is to use its thrusters to move itself from its current position (point A) to a second satellite in order to dock with it (point B). In theory it would be possible to calculate the exact magnitude and direction of the thrust to be produced by the thrusters. In practice however, these calculations include a number of significant uncertainties. We need to ask ourselves for example, whether we really know

(Photo: NASA)

A theoretical offshoot of the MISAT project – that nonetheless has a large number of possible practical applications – is the research on interval analysis, a mathematical method for solving numeric problems by means of a computer. Major application areas of the method include the so-called nonlinear optimisation problems. Although previous methods existed for such problems, these did not offer any guarantee that the optimal solution will be found. Interval analysis does offer such a guarantee.

A Soyuz spacecraft docking with the

Interval calculations are used

Autopilot landings might contribute to improved

International Space Station on 1 November

to determine the trajectories

flight safety. Important parameters required by

2002, as seen from inside the ISS. Satellite

that a satellite may follow given

the flight computer handling the landing would

miniaturisation can result in a loss of quality

the uncertainty in its initial position

include the aircraft’s position and attitude.

in sensors and actuators, which introduces

as well as the uncertainty in the amount

Using the interval method for solving the

uncertainties that will make autonomous

of thrust its propulsion system develops. Any

integer ambiguity problem, three GPS receivers

docking more difficult. The on-board control

action that will not get the satellite to the target

(one mounted on each wing tip, and one on

systems will have to take these uncertainties into

satellite, taking into account the uncertainties,

the fuselage) would suffice to calculate the

account as they try to optimise the approach

can be struck from the list of possible actions.

full attitude of the aircraft. To determine the

and docking manoeuvres.

This enables the system to calculate the optimal

aircraft’s position with the required extreme

trajectory to its target in an iterative process.

accuracy, an additional antenna will be required on the runway.

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the exact location of point A, the satellite’s current position, and the same applies to the destination, point B. It also remains to be seen whether the power and direction of the thrusters can be controlled with sufficient accuracy. Uncertainties like these can render a calculation based on clear and crisp values next to useless. Interval analysis does not assume singular values, but instead uses a series of values, an interval. Regarding position A it can be said that the satellite is certainly located between two points A1 and A2, and a similar statement applies to the destination point, B. The required thrust magnitude and direction for a number of possible trajectories between these two intervals can then be calculated. By repeating these calculations throughout the duration of the satellite’s flight, the optimal control settings for the satellite at any given moment can be calculated. Uncertainties “This is the only real solution if you’re dealing with uncertainties and possible measuring errors”, says Ir. Erik-Jan van Kampen. “In small satellites in particular, these uncertainties add up because the sensors and actuators are so much smaller and therefore less accurate.” Together with Ir. Elwin de Weerdt, Van Kampen is working on interval analysis at the Aerospace Software and Technologies Institute (ASTI) of the Aerospace Engineering faculty of TU Delft. In a few months they both hope to gain their doctorate for their research as part of MISAT. Van Kampen focuses on approach and docking procedures for satellites, and the subject of De Weerdt’s research is that of flying satellites in formations, or swarms. “My research looks at the most efficient way of moving a satellite into a specific position between a number of other satellites without hitting any of them in the process”, he explains. “How can we calculate the best trajectory to bring a satellite into position at a certain time using the least possible amount of propellant? Using interval analysis you can scan all the possible solutions, which enables you to find the best one.”


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Satellite

carrier wave

Other applications in which attitude verification is extremely important include the unmanned radiocontrolled aircraft (with a 3-m span) used by Heering UAS

Practical problems Interval analysis was developed during the 1950s and 1960s, but e.b=(phi+N)lambda didn’t gain much interest until recent years, with practical applications now being on the horizon. The main reason for this is that computers have now became so fast that they can perform large measurement: phi1 numbers of calculations in a relatively short time, e measurement: phi2 offering a means of solving many practical problems. b In addition to their MISAT research, Van Kampen and De Weerdt also worked on number of other problems, an important one of which concerned possibilities of using multiple GPS receivers to determine an aircraft’s attitude as well as its position by means of the GPS signal phases. If you determine the phase of the received GPS signal, you could in principle determine your receiver 1 receiver 2 position with an accuracy of a few millimetres. The problem is that the receivers cannot tell the phase difference between two Two GPS receivers measure the phase of the incoming different readings apart. They can tell the phase shift, but they satellite signal. The phase differences of the signal, which cannot know how many whole wavelengths need to be added. will probably vary for each receiver, are a measure of the This is a problem known as Integer Ambiguity. Together with Dr length and direction of the imaginary line (b) connecting the Ping Chu (their assistant supervisor) and Professor Bob Mulder receivers. Since the receivers cannot know in which wave they (their supervisor and professor at the Control & Simulation secare measuring the phase, there will remain an ambiguity in tion of the Aerospace Engineering faculty) Van Kampen and De the number of full waves between each pair of receivers. By Weerdt solved this problem using interval analysis. As a result using interval calculations to combine different satellites and of this work an aircraft fitted with three GPS receivers can now frequencies, these ambiguities can be resolved. Tests carried determine its exact attitude (including yaw, pitch and roll) in out with the Cessna Citation in use by TU Delft and the Dutch addition to its location relative to the Earth’s surface. The solution National Aerospace Laboratory (NLR) were able to validate the of this problem, for which a patent application has been filed, calculation methods developed by doctoral students Ir Elwin should enable an aircraft to land itself fully automatically. de Weerdt and Ir Erik-Jan van Kampen. Modeling Quite another problem that Van Kampen and De Weerdt looked at is how to model human perception, and a pilot’s perception in particular. To create a good flight simulator you need a model of the way in which a pilot reacts, e.g. how quickly he will respond to a stimulus produced by the simulator, or how strongly will he pull on the controls if something in the simulation makes him feel he should do so. The description of this behaviour turns out

to be a non-linear optimisation problem that lands itself well to an interval analysis solution. The nature of the work done by Van Kampen and De Weerdt is mainly theoretical, with an added focus on the implementation of the theory in the software. They explicitly avoided the hardware side of things. However, the range of possible applications is such that hardware implementation appears to be mainly a matter of time. The MISAT research

to prepare accurate contour maps.

Interval optimisation methods have also been used to identify perception models in pilots. Pilots’ behaviour in a simulator is compared with their behaviour in a real aircraft to find out how the simulator’s motions can be made more life-like. The changes are achieved by fine-tuning the simulator’s motion filters.

subjects form a point in case. If nanosatellites are to become capable of following the best possible trajectory in space, a hardware implementation of the research by De Weerdt is essential. And if nanosatellites are to be capable of docking with each other or with other objects, the research by Van Kampen could prove to be very valuable. The theory is clear. Now for the practical application!

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The amplifiers and filters in the masts of current mobile telephone networks are non-actively cooled. If they were to Image: Philip Broos

be actively cooled to extremely low temperatures (â&#x2C6;&#x2019;173 °C), their performance would improve by leaps and bounds. In areas with high population densities, the same number of masts would suffice for a much greater capacity. In areas with low population densities, like Australia, the cooled performance could be used to increase reception range, which equates to fewer masts per square kilometre.

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Pin-point cooling

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Small and vibration-free microcooler proves popular in satellite astronomy

269 °C) with a minimum of input power, and which does it all without any vibrations. The Cooling and Instrumentation research group at the University of Twente has managed to integrate microcooling and sorption cooling. The invention, which took some thirty man years of research and development, is being marketed by spin-off company, Kryoz Technologies.

(Photo: ESA and the SPIRE Consortium)

A cooler no bigger than the microchips and sensors it will be cooling, capable of reaching temperatures as low as 4 K (minus

Images of the deep infrared spectrum of the M74 galaxy at three

By Joost van Kasteren

different wavelengths. The images were obtained on 19 July 2009 using ESA’s recently launched Herschel telescope. These wavelengths

Brainwaves In addition to telecommunications there are many other applications in which vibration-free cooling of electronic circuits and sensors will yield improved performance. One example is the detection of weak infrared or x-ray sources in deep [outer?] space. Microcoolers can also be used to cool SQUIDs (Superconducting Quantum Interference Devices) to temperatures at which superconductivity occurs. SQUIDs can be used to detect very weak magnetic signals. One application is in medical diagnostics to measure foetal heart signals, or to detect brain activity. “Over a decade ago we ran into the problem that the equipment needed to cool microsystems is relatively large”, explains

Professor Marcel ter Brake, who is full-time professor in the chair of Energy, Materials and Systems of IMPACT, institute for energy and resources of the University of Twente. “To cool a sensor with a diameter of a few millimetres down to the temperature of liquid nitrogen requires a cooling plant that takes up a volume of about ten litres, including its casing. So, in 1997, together with Professor Miko Elwenspoek and Professor Horst Rogalla, we applied, successfully as it turned out, for an grant form the Dutch technology foundations STW [in full??] grant to see if we could use the University of Twente’s expertise in micromechanics to reduce the size of the cooling system, or at least parts of it.” Vibrations In this initial undertaking, Johannes Burger as PhD student in the project, realised a prototype microcooler, etched into silicon. It used an expanding gas fed through glass tubes. Reducing the pressure lowers the temperature to the point where the gas becomes liquid. The subsequent evaporation process extracts heat from its surroundings, cooling them (in this prototype) to a temperature of 165 K (−104 °C). Ter Brake: “In fact the cooling cycle is like that of an ordinary refrigerator, which also extracts heat by evaporating the cooling medium in a continuous process.” However, the common or garden fridge or freezer uses an intermittently running electric motor to compress the vapour phase, which was out of the question for the microcooler since the motor’s vibrations would

are the equivalent of the colours blue, green, and red in the visible spectrum. The images have been enhanced to bring out the galaxy’s intricate structure and background details. The image is at its sharpest at a wavelength of 250 microns. The combined image enables astronomers to perform calculations on the properties of the material emitted by the galaxy.

(Image: NASA/SAO/CXC)

“One of the major application fields is telecommunications”, says Dr Ir. Pieter-Paul Lerou, managing director of the company that was incorporated last year. “Together with the University of Twente we are developing a microcooler for use in mobile telephone masts. If you lower the temperature of the first amplifier stage in these stransceiver stations, the signal-to-noise ratio is improved, and a single antenna will be able to serve more mobile telephones. In Australia this will be useful because it means you can do with fewer antennas per square kilometre. In Western Europe it will enable us to accommodate the huge growth in mobile communications without increasing the number of mobile telephone masts at the same rate. Given the public resistance to antenna systems, this will appeal to telecom companies.”

X-ray image of N132D, the supernova remnant of a massive star in the Large Magellanic Cloud, a galaxy at a distance of 160,000 light years from Earth. The image was taken by the Chandra satellite launched by NASA in July 1993. The different colours represent different sections of the x-ray spectrum, with red, green and blue representing low, average, and high x-ray energy levels, respectively.

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interfere with the operation of the electronic circuits and sensors that were being cooled. Ter Brake: “This is why we opted for the sorption process to compress the gas. We use activated carbon as a compressor. It is a material with a large internal surface area, which can be used to store large quantities of gas. Adsorption is a physical process. There is no chemical reaction between the refrigerant gas and the activated carbon (as is the case with chemical absorption), which means that the material will not become degraded. Heating the activated carbon will desorb the gas and enable a high pressure to be created. When the gas is then allowed to expand, it will cool to the point where is becomes liquid.”

Dark current (e –pixel/s)

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(Images: ESA /AOES Medialab)

102 100 10-2 10-4 Drawing of the helium tank carried

Herschel satellite launched by ESA on

by Herschel. The three scientific

14 May 2009. This space telescope

instruments are arranged on top, and

includes a 3.5-metre mirror, the largest

will be covered by a hood to create a

ever to be launched into space. The

cryostat. The tank contains 2367 litres

light from the telescope hits three

of superfluid helium, making it the

scientific instruments, including a

largest component of the satellite. If

spectroscope. Dubbed HIFI, this was

the cooling technology developed by

developed by a consortium led by

Twente University had been used, the

SRON in Groningen. The telescope

size and weight of the satellite would

covers a section of the far infrared

have been drastically reduced without

spectrum reaching into the sub-

affecting the performance of the

millimetre range, and is designed to

instruments.

study the coldest and furthest objects of the universe, which cannot be done from Earth due to atmospheric disturbance. To protect the instruments and maintain the highest possible sensitivity, superfluid helium is used to cool them to −273 K (0.3 °C above absolute zero).

160 180 200 220 240 260 280 300 320 340 Temperature (K)

Intrinsic noise of an optical silicon-based detector.

(Photo: Thales Cryogenics, Eindhoven)

Artist’s impression of the European

An example of commercially available coolers. These coolers were developed mainly for military applications and have cooling capacities in the range of 0.1 to 10 watts at a temperature of 80 K, a bit excessive for electronic circuits dissipating energy in the milliwatt range.

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Microsatellite A few years ago, the development of the microcooler and the sorption-based compressor was combined in a research project undertaken as part of the MicroNed programme. The research focused on developing cooling systems for microsatellites, a project of the Aerospace Faculty of TU Delft. Ter Brake: “Microsatellites, or even nanosatellites, provide a low-cost option for space missions. The question for us was, what would happen to the satellite’s heat balance if it was scaled down. It would probably become critical for a number of the satellite’s components. A microcooler might then provide a solution.” The combination of microcooling and space exploration didn’t just appear out of the blue. Between 2003 and 2006 Ter Brake’s group conducted a research project for the European Space Agency, ESA, which was continued in 2008. The researchers were looking for vibration-free cooling systems for use in spectroscopes searching for infrared and x-ray sources in the universe. Cooling a spectroscope detector improves the signal-to-noise ratio, which enhances its detection capabilities. The project, which was funded by MicroNed and allowed a postdoc researcher to be appointed, led to the integration of the microcooler and the sorption compressor into a cooling system with an overall volume of half a litre. It is a gas-liquid system, in which activated carbon acts as the medium for building up pressure, and in which two buffer tanks are used for the intermediate storage of highpressure and low-pressure gas. The design is remarkable for its heat exchanger, in which the high-pressure gas, before expanding, is cooled by the returning low-pressure gas.


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Three sheets of glass As mentioned above, the first prototype of the cooling tip used a combination of silicon with glass tubes to transport the gas. The cooler was difficult to make, but it did prove that it was possible to make a microscopically small cooling tip capable of providing vibration-free cooling down to temperatures in the order of magnitude of 160 K. The next step was to optimise the thermodynamics of the microcooler, a task Ir. Pieter-Paul Lerou has occupied himself with these past few years. “The thermodynamics of the unit are somewhat critical”, Lerou says. “The gross cooling capacity is of the order of magnitude of 40 milliwatts and to bring about the actual cooling you need a net power in the order of magnitude of 20 milliwatts. This means that your thermal losses must not exceed 20 milliwatts, or you will run the risk of condensing little or no gas, and you will fail to reach the required temperature.” The thermodynamic optimisation resulted in a certain geometry of the microcooler and the use of specific materials, or rather material, which in this case is glass, a good thermal insulator. In its final guise the cooler consists of three stacked sheets of glass with a length of 17 millimetres. Warm (room temperature) high-pressure gas is fed to the cooling tip through a channel in the topmost layer of glass, and exits through a nozzle etched in the glass. From the cooling tip the cold, low-pressure gas flows back through a channel in the lower glass sheet. The two sheets of glass with the low-pressure and high-pressure gas flows are separated by the third – very thin – sheet of glass, which uses contact conductivity to act as a heat exchanger between the two gas flows. Unique Manufacturing the microcooler, which is far from simple, takes place at Micronit Microfluidics in Enschede, a company set up by a group of the University of Twente graduates and which specialises in the design, development, and manufacture of microfluidics devices, as used in ‘labs on a chip’. Micronit R&D manager Dr Ir. Marko Blom: “We use a single type of glass to avoid creating stresses caused by different coefficients of expansion. We have a separate wafer for each layer, so a total of three wafers. The manufacturing process involves six masking steps and ten tooling steps, each of which involves several

4

1

2

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3 5 8

10 9 P H

6

7

Schematic diagram of

P

L

the Linde-Hampson sorption cycle with Joule-Thomson

13

12 11

expansion. The

Demonstration microcooler constructed as part of Johannes Burger’s

activated carbon is

doctorate research in 2001. The heat collector with its five compressor

held by the container

cells below it is cooled by means of a fan (which has been removed

(1) which is separated

for this picture). On the right are the gas connections of the five cells.

by a gas gap (3) from

Next to these are two flow meters that measure the gas flows on

the heat collector (5).

the low-pressure and high-pressure sides. The triangular case is the

The gas gap actuator

vacuum space containing the cooling stage.

(2) contains a small

quantity of carbon with a specially selected contact gas. The carbon is heated to release the contact gas, which fills the gap to establish a good thermal contact between the container and the heat collector. This cools the carbon inside the container down to the temperature of the heat collector, and adsorbs gas in the container until the pressure drops to the point at which the low-pressure valve (7) opens, and refrigerant gas from the low-pressure buffer (8) is adsorbed by the carbon in the container. When the carbon in the container is saturated with refrigerant gas, the gas gap actuator is no longer heated, causing the contact gas from the gas gap to be adsorbed by the carbon of the actuator. This creates a thermal insulation between the container

Cooling stage of the 2001 demonstration microcooler, which uses

and the heat collector. The carbon in the container is then heated

three 9 mm × 9 mm silicon chips, and which is connected though glass

by an internal heating element (4), causing the refrigerant gas to

tubes. The thicker tubes in the picture are in fact pairs of concentric

be desorbed and the pressure inside the container to rise. As soon

tubes that together form the counterflow heat exchanger (high-

as the pressure in the container exceeds the pressure inside the

pressure gas flows through the inner, and low-pressure gas flows

high-pressure buffer (10), the high-pressure valve (9) opens, and

in the opposite direction through the gap between the two tubes).

high-pressure refrigerant gas flows from the container through the

The thin glass tubes were added to provide mechanical stability. The

aftercooler (6) and into the high-pressure buffer. From there the

chip at the top left is the splitter which divides the counterflow heat

gas flows through a counterflow heat exchanger (13) and through a

exchanger into two gas lines; the chip halfway along the tubes is a

restriction (11), where it expands and cools off as a result of the Joule-

condenser in which a thermoelectric element cools the refrigerant gas

Thomson effect. As it cools, the refrigerant gas condenses, and collects

to the point at which it condenses. The chip on the right is where the

as a liquid in the evaporator (12), at which point the cooling system’s

liquid expands and drops still further in temperature. This chip also

refrigerating power becomes available for use.

contains the evaporator.

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Temperature plot of the demonstration microcooler when cooling. The broken line shows the temperature of the condenser, while the other line shows the evaporator temperature. When the condenser reaches approximately 230 K (−43 °C), the refrigerant (ethylene) liquefies and the temperature of the Joule-Thomson tip containing the evaporator drops much more rapidly.

3D design and end product of the cold stage of a second-generation

The microcooler has a capacity of 20 milliwatts at −173°C. This version

micro-cooler. The cold stage consists of three very thin layers of glass

from 2004 still needs to be fed nitrogen from a gas bottle.

that are atomically flat. The layers bond immediately when they are stacked together. No adhesive is required.

Close-up view of the evaporator at the end of the cold stage, which

Glass wafer with 15 designs for the intermediate layer of the

is attached to the electronic circuit that needs to be cooled. The

microcooler, as manufactured by Micronit Microfluidics. The

attachment method is very important and still the subject of research.

intermediate layer contains the heat exchanger ducts. During the manufacturing process, which includes etching and powder blasting, 50% of the material is removed. With so much material being removed, tensions build up inside the wafer, which makes the bonding of the three glass layers into coolers a highly demanding process. After years of research Micronit is now capable of bonding over twenty layers of glass into a single monolith.

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process steps. The tooling steps include etching and powder blasting to create a three-dimensional structure on and in the glass. I think I’m safe in saying that we’re one of the very few, if not the only, company in the world that can do this.” When all the steps have been completed, the wafers are bonded together. Blom: “The surface of the glass is so pure that we can just stack them and raise the temperature to make the sheets stick permanently together. There is no glue or solder involved, nor could there be, because an extra layer would interfere with the thermal properties. Once the wafers have been bonded together, the individual microcoolers are separated. Each wafer holds twenty microcoolers, which makes it a relatively large product when compared with microchips. The manufacturing process is still semi-automated, because we’re dealing with small batches. Once the numbers increase, it will become worthwhile to fully automate the entire process.” “There’s a very real chance that the numbers will be increasing in the near future”, Lerou says. “When the capacity of mobile telephone masts increases substantially thanks to our coolers, I expect the demand to increase considerably.” Square kilometre array Another application field that may stimulate the demand for microcoolers is radio astronomy, and in particular the so-called SKA antennas like the system being constructed by ASTRON at Dwingeloo. These square kilometre array antennas are designed to pick up and locate weak radio signals coming from space. They consist of thousands of simple antennas spread over a large area. The microcooler could be used to dramatically improve the signalto-noise ratio, just like it does in telecom systems. Lerou: “Proper cooling would allow the number of antennas to be halved, or even quartered. Even though each antenna does not cost much, it would save a lot of money. You would also reduce the cost of signal processing. And to further lower the costs, we are looking at distributed cooling options, with a single compressor serving 64 microcoolers.” Distributed cooling would also be very useful in satellites. To save space and weight, it would be nice if several microcoolers could be connected to a single sorption compressor. The best configuration for a distributed cooling system is currently being explored


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by several parties, including the European Space Agency, ESA. All in all, the combination of a vibration-free sorption compressor and a microcooler that can be made to measure for any sensor or chip appears to be a promising option for a host of applications varying from telecommunications to space exploration and medical diagnostics. Lerou: “The great advantage is that you can offer it as a fully integrated package, a closed system with a long service life and without any vibrations. Embedded cooling, if you like, a completely new concept in this market.” For more information, please contact Professor Marcel ter Brake, phone +31 53 489 4349, e-mail h.j.m.terbrake@tnw.utwente.nl, or Dr Pieter-Paul Lerou, phone +31 53 203 0995, e-mail pieter.lerou@kryoz.nl, or Dr Marko Blom, phone +31 53 850 6850, e-mail marko.blom@micronit.com.

300 280

Cold-stage temperature [K]

260

The application of microcoolers in SQUID technology, as used in brain

The Delfi-C3 nanosatellite developed by TU Delft and launched on

research, can improve the imaging quality.

28 April 2008.

240

An artist’s impression of the Square Kilometre Array (SKA) that is

220

being realised at Dwingeloo in the Netherlands by ASTRON. The SKA will be two orders of magnitude larger than existing radio telescopes,

200

resulting in a proportionally greater sensitivity. This unprecedented

180

sensitivity will be a major step forward in gathering knowledge about

160

the Big Bang, the theory of relativity, the formation of stars, and the origins of life.

140

The sensitivity of SKA, with its large number of receivers (107), is

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100

determined to a major extent by the noise introduced by the first

0

200

400

600

800

1000

1200

Time [s]

amplifier in the receiver chain. Cooling this amplifier will greatly improve the signal to noise ratio. To enable this to be done on such a large scale, a microcooler will probably be the only viable

Cooling curve of the second- generation cold stage. The tip cools from room

option. Two other locations are still competing for the realisation

temperature to about 100 K (−173 °C) in roughly fifteen minutes. The cooling

of the SKA, Australia and South Africa. The so-called ‘First light’ is

time of the current generation has already dropped far below ten minutes.

expected for 2020.

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The European ENVISAT satellite, used for observing climate changes and environmental pollution, and launched in

(Image: ESA

2003, is the largest satellite ever built by ESA. Immediately following its launch, the solar sensors were used to make the satellite position its solar panels to face the sun in order to optimise its power supply. The solar sensors are also used in the event of such calamities as malfunctions in the subsystems that handle the accurate positioning of the satellite itself.

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The first autonomous solar sensor Micro Micro

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Miniature satellites demand smaller sensors using less power

Satellites come in all sorts and sizes, with the largest as big as a good-sized bus, and the smallest, known as CubeSats, measuring only ten centimetres cubed. Earlier this year the first Dutch nanosatellite was launched into space. The satellite, Delfi-C3, measures 10 × 10 × 30 cm. If a satellite that size is to be able to carry any form of payload, the subsystems controlling the device and keeping it in its earth orbit, need to be considerably smaller than recent standards. Researchers at TNO have succeeded in creating a small, low-power solar sensor that provides it own energy. The plan is to reduce the size of the sensor a further ten times. If everything goes according to plan, the Delfi-n3Xt satellite will be launched in 2012. Ever since the nineteen seventies TNO has been developing and

By Arno Schrauwers

producing solar sensors for the global satellite market. The sun acquisition sensor is one of the first sensors developed in Delft.

Solar sensors are used to optimise the attitude of a satellite relative to the sun in order to maximise the yield of the satellite’s solar panels. TNO Industry & Technology, formerly and famously known as TPD, has been manufacturing solar and stellar sensors since the late nineteen sixties, and dozens of satellites have been launched since with TPD sensors on board. The 3-tonne Rosetta probe, which was launched in 2004 on a mission to Comet 67 P/ Churyumov-Gerasimenko (which it will reach in 2015), and the Mars Express vehicle which is currently orbiting the red planet, also contain TPD-sensors. TNO is one of only five prominent manufacturers of solar sensors in the world. A research group at TNO Industry & Technology, in collaboration with TU Delft, has now developed a solar sensor a fraction of the size of current types. The miniaturisation fits in with the trend towards smaller satellites. The solar sensor also carries its own power supply in the form of highefficiency gallium arsenide solar cells (offering an efficiency of over 26%), which contribute a large part to the miniaturisation. “Microsatellites and nanosatellites aren’t suitable for telecommunications”, says Johan Leijtens, system designer at TNO Science & Industry, “because they can’t deliver enough power. On the other hand, small satellites are very useful for all kinds of earth observa-

tion applications such as detecting potentially harmful cyanobacteria in surface waters, monitoring crops, or locating crops that could be turned into narcotics. If you want more updates of the areas under surveillance, you will need to put up more satellites, and small ones come cheaper than large ones. Rather than 1.3 billion euros, which is the cost of the big Envisat satellite carrying instruments that include TNO’s SCIAMACHI atmospheric pollution detector, a single small satellite would cost only a few million euros. The U.S. Air Force Research Laboratory has already shown its interest in the TNO solar sensors for use in small spy satellites. The solar sensor’s use isn’t limited to space exploration; you could also use it to align solar panels on top of buildings, or to measure the optimum light settings for market garden greenhouses.” Photodiode array Although solar sensors are essential if satellites are to get the most out of the available solar energy, a solar sensor is in fact a simple device. It consists of a membrane with a pinhole in it, and a few millimetres behind it, an array of photodiodes used to measure the angle of incidence of the light entering through the pinhole. However, with all its external electronics, the power supply, and the

The photodiodes are mounted on a central cube-shaped structure and look for the sun to peep over the edge. The accuracy is about 3°.

In the second half of the nineteen eighties a membrane with a 6 × 6 mm aperture was added above the photodiodes, increasing the accuracy of the solar sensors to 0.2°.

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The three most commonly used TNO solar sensor types. The sensor

high-accuracy membrane-type solar sensor (accurate to within 0.2°).

on the left is a low-accuracy (3°) model, the one in the middle is a

The model on the right is very small, but less accurate (5°).

In the nineteen nineties TNO introduced a digital solar sensor. The digital device can easily distinguish between the sunlight and the light reflected by the earth, so the Albedo effect no longer plays a role.

The size of solar sensors is determined largely by the power supply system. The sensor on the left operates using a stabilised 6.5 V power Images: TNO Delft

source. The one in the middle runs on an unstabilised 28 V source, but uses its own circuitry to stabilise the power, increasing its size almost twofold. TNO and the Harvast Imaging company have developed a new sensor optimised for low power consumption. The 368 × 368 array of photodiodes uses very little energy, which makes it possible to use a small dedicated solar cell to power it. As the unit’s height would have been dominated by the size of the connector, it was decided to use an RF datalink instead.

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connections, it still ends up as a fist-sized device weighing a pound. Sensors are essential components of a satellite, but you need to minimise their share of the total in order to maximise the payload capacity in the form of earth observation equipment, transmitters, receivers, etc.. And then there is the trend towards miniaturisation. Leijtens: “This had a lot to do with cost. A large satellite like Envisat, with TNO’s SCIAMACHI instrument on board, weighs about 13 tonnes and costs about 1.3 billion euros including the launch. Microsatellites or nanosatellites on the other hand are the size of a beer barrel with an all-up weight of about 150 kg, and cost 15 to 20 million euros for the satellite and 50 to 100 million euros for the entire mission, with a large chunk of the cost being related to the development of the mission. If you build multiple satellites carrying identical instruments, the construction cost per unit can be reduced considerably, down to the order of magnitude of 25 million euro each for a series of ten satellites. This is a relatively small investment, which renders the concept attractive for a wide range of earth observation applications.” Reproducibility Leijtens started on the development of a smaller solar sensor in 2004 as part of the MicroNed programme. The research organisation is collaborating with the TU Delft and the Belgian company, Harvest Imaging, founded by Professor A.J.P. Theuwissen of the Department of Electronic Instrumentation at TU Delft. The heart of the newly developed solar sensor is a microchip measuring just 5 mm by 5 mm. Leijtens: “We integrated all the control and signal processing electronics on that single chip. They include 368 × 368 pixel active light sensor and a special electronic circuit that quickly and efficiently determines which of the photodiodes in the pixel sensor are being illuminated by the sun’s rays. The essence of a sensor like this lies in having the best possible reliability and reproducibility. The reliability has been improved by integrating as many functions as possible on a single chip. The reproducibility for the sensor as a whole is achieved by accurately checking a number of physical dimensions that must be maintained during production. Miniaturisation reduces all these dimensions, which makes it increasingly difficult to maintain the required precision.”


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The AWSS solar sensor as currently orbiting on board the Delfi-C3 satellite, launched on 28 April 2008. This is a high-accuracy analogue solar sensor (accurate to within 0.5°) with an autonomous power supply, and a wireless data link (915 MHz) replacing wiring and a connector. Its volume (4 × 6 × 2.8 cm) is determined mostly by the conventional photodiode, the membrane, and the electronics. The antenna is protected by a polyurethane coating.

Photo: TNO Delft

Glass sheet To manufacture another crucial element of the sensor, the membrane that covers it, two techniques were tried that might produce the required precision of approximately 10 micrometres. The first of these is the chip technique, in which the pinholes are etched into a silicon wafer coated with silicon nitride (a method that makes it possible to manufacture a batch of membranes simultaneously). The second (patented) technique uses a sheet of glass, the back of which is coated with a non-reflecting layer onto which the pattern of electrical connecting tracks is applied. The front carries the membrane and an absorption layer to avoid reflections, which would interfere with the measurements. The sensor itself, with all its integrated electronics, is a miracle of technical ingenuity. But there is more to it than that. The power supply is another problem area in sensors. Normally speaking, solar sensors draw their power from the solar panels carried by the satellite, but this energy needs to be distributed among the many other power-consuming systems on board. Again, as with the mass, economy is of the essence. Also, satellites have their own distribution voltage, which varies from satellite to satellite. It’s usually 28 volts (either stabilised or not), but telecom satellites for example often use 110 volts, which means you will need to add a converter to create the right voltage to power the sensor.

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On 17 April 2007, seven CubeSats were released in space after being launched as secondary payload aboard a Dnepr rocket. Immediately after deployment, the U.S. Aerospace Corporation’s AeroCube 2 took this picture of one of the other CubeSats, the CP-4 satellite developed by California Polytechnic State University.

Independent The new solar sensor produced by TNO has its own built-in power supply, which according to Leijtens makes it the first satellite sensor to operate independently of the satellite’s internal power system. The high-efficiency solar cells used for the power supply are made of germanium with a sensitive layer of gallium arsenide. They will convert at least 26% of the incoming solar energy into electricity, whereas your common or garden silicon cell won’t exceed 10 to 12%. The high efficiency is the result in part of the layered construction of the solar cells, which enables a large part of the sun’s visible and UV spectrum to be converted into electrical energy. The solar sensor itself is far from wasteful, and needs only 25 milliwatts to read and process its data. Its radio frequency (RF) communication system requires another 25 mW, bringing its total power consumption to 50 mW. This means that the sensor can make do with a small solar cell for its power needs, small enough to be mounted on the sensor housing.

Six months before launch the AWSS solar sensor is being installed in the Delfi-C3 nanosatellite in the cleanroom at the Aerospace Faculty of TU Delft, under the watchful eye of Johan Leijtens.

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Top view of the central structure of the Delfi-C3 nanosatellite, with the AWSS sensor and the four solar panels on top. The solar cells developed by Dutch Space (at the tips of the panels) are flexible and are currently being flight-tested. At its lower end, the satellite carries

Photos: TNO Delft

the second solar sensor (not visible).

Researchers at TNO are experimenting with mounting the sensor and the membrane on a single sheet of glass in order to further reduce the size of the solar sensor.

The result is an ultra small, yet still analogue, solar sensor mounted on a piece of radiation-resistant glass (so it will not discolour when hit by cosmic rays). The frame on the left contains the glass substrate with the membrane, with the actual sensor below it. The other side of the sensor can be seen on the right. The frame (with its mounting holes) is considerable larger that the sensor itself.

Macro image showing the prototype of the specially developed APS+ imager. The sunlight hits the array of photodiodes (pixel array). The signal is processed in the column on the right. An A/D convertor will soon be added. This chip was developed in collaboration with Harvast Imaging and TU Delft.

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RF communication The radio frequency data link is another first. The sensor’s measurements need to be fed to other parts of the satellite so it can change its attitude if necessary. The connector used for this purpose on the old type of sensors took up a lot of space, Leijtens says. “So, we incorporated a wireless data link system that relays the sensor data by means of radio waves. The RF section occupies about half the overall volume of the new sensor, but as the size of the sensor is still determined by the size of the solar cell, it doesn’t matter. What does matter though, is that the use of RF enabled us to reduce the height of the sensor by some 80%. We probably won’t be able to reduce the size of the unit much below two square centimetres if we continue to use a radio frequency data link, because we will always be restricted by the radio frequencies used, and ultimately the antenna will dictate the size of the system. A smaller antenna means higher frequencies and higher losses. Optical solutions might become an option, but suitable VCSELs (Vertical Cavity Surface Emitting Lasers) have a much lower power efficiency than an RF system, which would mean using a larger solar cell. These are very interesting developments to keep tabs on though, because semiconductor lasers are also becoming increasingly efficient. As the RF field is also rapidly developing, we cannot tell yet which system will turn out to be the smallest.” As the solar sensors are reduced in size, positioning problems are introduced. Positioning is done using an alignment aid, but this has a lower limit. If the device to be positioned on the satellite becomes too small, its alignment becomes less accurate. The solution would be to include the solar sensor in a larger system including, for example, GPS instruments and star cameras. “We’re working on that too”, Leijtens says, “together with a large number of Dutch small and medium-sized companies. The project is being supported by the Netherlands Space Office as part of the Prequalification ESA Programme (PEP) scheme.” Reliability “TNO and its partners are currently working on the reliability of the system. This is a factor of great importance during the sensor’s operational life, but it is also essential if we are to be able to put the thing together without problems. Next year we will complete the project by delivering a glass substrate sensor, the immersed technology, and a chip with a digital solar sensor. The remarkable


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thing is that only a year ago we failed to secure an ESA order for the development of a new solar sensor. The order went to a competitor, even though our technology at the time was also considered very good. I can safely say that our current design puts us clearly ahead of the competition. For example, their sensor clearly had a higher power consumption because it used a less intelligent method for scanning the sensor’s photodiodes. They are using a separate microprocessor, with all the bother that involves. Our sensor on the other hand has been truly optimised for this particular application.” “We have loads of new ideas, not just about the design itself, but also regarding the applications. The U.S. military is interested, and NATO is studying the possible use of small observation satellites to provide a cost-effective option for covering white areas in war zone reconnaissance. The currently available observation satellites are mostly used to monitor the former Soviet Union, but we have nothing up there to cover, say, Afghanistan or Africa. Microsatellites could prove to be a low-cost and easy to launch platform. The miniaturisation of the sensors and the resulting cost savings bring all kinds of new applications within reach both here on earth and out in space. We’re about to witness an application boom.”

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High ep silon

High epsil on

The eventual performance of the sensor will depend to a large extent on the

Refle cting layer

properties resulting from the various

Stray light coati ng

thin-film coating steps. Even though the naked eye can only see a sheet of glass

Carrie r

with a sensor mounted on it, the glass also incorporates a layer with a high

Anti refle x coa ting

emission coefficient to ensure that the sensor will not get too hot. It further

Sens or

Sunse nsor

The plan eventually, as part of the next phase, is to integrate an efficient

Absorb ing la yer

solar cell into the unit, to be connected

Carrie r

through the substrate to the electronics

Anti re flex co ating Elektr onic ci rcuits RF-cir cuit

incorporates the reflecting membrane

on the underside. This will create a fully autonomous sensor on a glass substrate. The principle has already been patented by TNO.

Senso r

with the aperture, an absorbing layer,

an antireflection layer on the underside, and a number of layers to provide the electrical connections.

This recently (2010) produced mini digital sunsensor is based on the APS+ sensor, but it is neither autonomous nor wireless. It is due to the rather conservative approach of the space companies. The sensor is now the stepping stone towards the originally intended autonomous and wireless version, with core properties such as low power and small size. Compared to the conventional digital sunsensor, the volume and mass are more than one order of magnitude less, while the power consumption

For more information, please contact

is reduced from 1.4W to 55mW. Novel manufacturing methodes combined with a

ing. Johan Leijtens, e-mail johan.leijtens@tno.nl

severely limited number of components is expected to bring down the price of the sensor significantly..

Albedo

Thanks to special electronic circuits the imager uses very little energy. The chip contains special hardware that detects the brightest pixel for each row and column in a single clock cycle, providing a smart way of reading the array of 512

The development of a dedicated power supply and the integration of the various functions onto the microchip weren’t the only new features of the TNO design for the solar sensor. Leijtens: “We started by focusing on detailing the glass substrate assembly, the so-called immersed technology, in which solar rays pass through the glass, and on the design of the microchip. We really have too many new ideas to work on them all.” The researchers did manage to look for a solution to a problem that occurs when analogue sensors are used. These are more reliable than digital sensors, because they require fewer electronics and can therefore run on

less energy. The problem with analogue sensors is that they are affected by the albedo, which is the sunlight reflected by the earth. The albedo can severely affect measurements by satellites, some of which orbit the earth at altitudes of only five to six hundred kilometres. In digital sensors the interference is fairly simple to remove by filtering, although this requires additional electronics. The solution is to use sensors that measure wavelengths at which the earth’s albedo appears dark (i.e. does not emit light). By using this effect it would appear to be possible to build solar sensors that are not only insensitive to albedo, but also use microwatts rather than milliwatts.

× 512 photodiodes.

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Innovative mic 2012 will see the launch of the Delfi-n3Xt microsatellite, the successor to Delfi-C3, which was launched in 2008. Unlike its predecessor, Delfi-n3Xt will be fitted with a microthruster that will enable the satellite to change its position at any time. It will be one of the smallest and most innovative microthruster systems orbiting the Earth. MicroNed researchers have carried out its design, manufacture and testing.

(Photo: Indian Space Research Organisation ISRO, Bangalore, India)

By Bennie Mols

On 28 April 2008, a rocket was launched from a space compound near the city of Chennai on the east coast of India, carrying the Dutch Delfi-C3 satellite into orbit. Unlike most satellites orbiting the Earth, which are large and heavy, this satellite is small and light. Delfi-C3 has a volume of three litres â&#x2C6;&#x2019; it measures 10 by 10 by 30 centimetres â&#x2C6;&#x2019; and weighs about three kilogrammes. It draws its power from solar panels, and communicates with the ground station via long, thin antennas that extend like tape measures.

The launch of a PSLV rocket carrying ten payloads including the Dutch Delfi-C3 nanosatellite from the space centre of the Indian space organisation, ISRO, on the southeast coast of India on 28 April 2008.

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For many decades satellites have tended to become increasingly heavy and more complex. Driven by the cost of premature malfunction or even the total loss of a satellite, quality control gained in significance, escalating the cost of space missions. In addition, it was taking longer and longer for satellites to become ready for launch. Anyone looking for a carrier to take small experiments into space might have to wait ten years before an instrument could


rothruster for Delft microsatellite

MilliNewtons Delfi-C3 still sends in its reports from space via a daily radio link, providing a perfect demonstration of a first-generation nanosatellite in space. Using the principle of swarm logic, future generations of microsatellites may have to be able to fly in strict formation with possibly dozens of other microsatellites, maintaining their relative position within tight limits. This is where microthrusters come in, a minute rocket engine capable of carefully nudging a microsatellite into position while in orbit. The launch of Delfi-n3Xt, the successor

Artist’s impression of Delfi-C3 in orbit. The transmitter and receiver antennas and the solar panels are positioned so as to ensure optimum communication and Image: TU Delft

Delfi-C3 embodies a new satellite philosophy developed in the United States during the late 1990s, which was to start making satellites smaller and lighter rather than bigger and heavier. Satellites up to 500 kilogrammes were called microsatellites (those weighing 10 kg or less are more correctly known as nanosatellites). In other words, the credo has become ‘small is beautiful’. In microsatellite design, the main limiting factor isn’t weight, as it is in large satellites, but volume. This means that miniaturisation is a must. Fortunately, the development of microsystem technology started around the 1980s, enabling increasingly small electromechanical systems to be developed, including valves, filters, sensors, microcoolers, solar sensors, and now thrusters. Delfi-C3 was the first microsatellite to be developed in the Netherlands. Future developments may result in swarms of microsatellites flying through space in formation. They could be used to observe the Earth, for example, or inspect a space station on the outside. Together they would perform just as well as, and perhaps even better than, a single large satellite. The great advantage of using a swarm is that it would be much less vulnerable than a big satellite. Even if one member of the swarm were to fail, the remaining satellites would still be able to carry out their scheduled tasks. The strategy for successful survival of a colony of bees or ants depends on the same principle, swarm logic.

of Delfi-C3, has been scheduled for 2012. Delfi-n3Xt has the same external dimensions as Delfi C3 – 10 × 10 × 34 centimetres – and will be one of the world’s first nanosatellites to be fitted with a micro propulsion system. MicroNed provided additional funding to enable this new technology to qualify for the job. Ir Berry Sanders MBA of the TNO Defence, Security & Safety Core Area in Rijswijk is the coordinator of the Dutch programme in which TNO collaborates with researchers from TU Delft and the University of Twente to develop the micro propulsion system. “Our challenge was to miniaturise the rocket thruster system”, Sanders explains, “to obtain a small thruster that would produce sufficient thrust. We also needed to be able to control the amount of thrust with great precision.” A thruster generally consists of a pressure chamber in which a propellant gas is generated or stored, a valve that controls the flow of gas from the pressure chamber, and a nozzle in which the discharged gas accelerates. The nozzle has an hourglass shape. As the gas flows through the converging part of the thruster, it accelerates until it reaches the speed of sound in the narrowest section (the throat). The accelerated gas then flows out into space through the diverging part of the nozzle, reaching velocities far above the speed of sound. In order to deliver small (milliNewton) thrusts, the nozzle has to be very small. Typically the throat has a radius which is much smaller than a millimetre. This, combined with the low pressures in space, can result in nozzle dimensions of the order of magnitude of the free space between the gas molecules. This can cause the thruster’s performance to sink to unacceptably low levels. The task of the researchers was to find out which nozzle diameter, shape, and roughness would still provide sufficient thrust to move the microsatellite in space. The thrusts involved are of the order of magnitude of only a few milliNewtons, about a thousandth of a millionth of what a large, conventional thruster produces. “And this is the result”, Sanders says, holding up a ten by ten centimetre printed circuit board. On it, a small buffer tank (plenum)

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power generation in spite of the satellite’s tumbling.

Image: TU Delft

finally be accepted on a mission. Universities in particular suffered from these problems.

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Artist’s impression of the Delfi-n3Xt satellite, which is to be launched in 2012. The main innovation of Delfi-n3Xt in relation to Delfi-C3 is its active attitude control system, which uses electromagnetic coils and reaction wheels. The system is experimental, but will be used to aim the payloads and, if possible, the microthruster. It is expected that the microthruster will enable future nanosatellites to move into and maintain specific orbits, and enable them to participate in swarms.

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Image: TU Delft

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Based on a successful demonstration for the SME-LET programme, TNO and Bradford Artist’s impression of three satellites flying in formation. As part of a

Engineering were commissioned

swarm satellites will not need to maintain strict formation, only having

to demonstrate the gas

to stay in each other’s vicinity while maintaining some distance, like a

generators (measuring

flock of birds. This minimises the requirements for the thruster, which

45 × 150 mm) in space

can thus be made smaller and lighter. For many applications, including

on board the Proba-2

the OLFAR radioastronomy project, it is more important to know

satellite, which was

exactly where a satellite is than it is to move it into a specific position.

launched from Russia on 2 November 2009.

Within Microned’s MISAT project, TNO, TU Delft, and the University of Twente have continued the miniaturisation of the technology by creating a propulsion system for use in cubesats. Miniaturisation techniques were

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TNO, together with the Bradford

developed within Microned for the

Engineering company, made a first

valves and sensors. As a result the size of the

attempt at miniaturising cool gas

gas generators could be reduced to twenty percent

generators for use in space in 2004

of the original. This 10 × 10 cm engineering model used for

– as part of the Small and Medium

testing carries 8 cool gas generators (each containing 0.3 grammes

Enterprises – Leading Edge Technologies

of propellant). Weighing about 130 grammes, the model has

(SME-LET) programme of the European

demonstrated the feasibility of this type of system. The electronics

Space Agency (ESA). The system contains 12 cool gas

that communicate with the satellite’s on-board computer system

generators, each weighing a few grammes, around

are used to control the valve and the gas generators, and to provide

a shared buffer tank in which the gas is stored for

pressure and temperature sensor readings. This system was

later use.

successfully tested on the ground in 2007.

containing eight cool gas generators has been mounted. The cool gas generators can replenish the tank eight times with the propellant, nitrogen gas, which will then be released by a microvalve to pass through the micronozzle (integrated with the valve) before flowing out into space and nudging Delfi-n3Xt into position. “This is one of the smallest and most innovative thruster systems to be used in flight”, Sanders continues. “It is about one tenth the size that could be achieved using conventional technology.” Based on this engineering model the researchers are building a qualification model which will be used for the final qualifying tests, and which should be identical to the flight model. Dr Marcus Louwerse of the University of Twente made the thruster’s microsystems, Ir Barry Zandbergen of the Aerospace Engineering faculty of TU Delft simulated and tested the minute thruster, and TNO Defence, Security & Safety finally, integrated all the components into a unit. The entire project was funded mostly by MicroNed, with TNO, the University of Twente, and TU Delft also contributing. All in all the research and custom work took between ten and fifteen man-years. Flow simulation The eight small cylinders in the gas tank on the printed circuit board are miniature cool gas generators, as Sanders explains. They do not contain pressurised gas, but an electric signal will start a chemical reaction in one of the generators to produce nitrogen gas, which is then stored in the casing containing the gas generators, which doubles as a buffer tank. Whenever necessary, the microvalve opens and allows the nitrogen gas to flow from the buffer tank through the nozzle and out into space. The world’s rocket builders had ample experience with large thrusters, but this does not automatically apply to microthrusters, which are so much smaller and produce a much less dense gas jet. Within the FUNMOD (Fundamentals, Modeling and Design of Microsystems) cluster at MicroNed, researchers from Delft studied the differences between gas flows in microthrusters and conventional rockets. “A gas jet passing through a small nozzle encounters more resistance than a jet flowing from a large aperture”, says FUNMOD cluster leader Professor Daniel Rixen of TU Delft. “This reduces the thrust, which means you can no longer simply apply the classic design rules for thrusters.”


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Thin air The researchers at FUNMOD generally study problems of a fundamental nature, not aimed at any specific application. However, they thought the microthruster would be a good test case to link fundamental flow research to a practical application. Doctoral student Federico La Torre and Professor Chris Kleijn of the Multi Scale Physics department of TU Delft used a computer to simulate the gas flow in the microthruster to find out how the thrust efficiency depends on the shape, size, and wall roughness of the nozzle. “We were faced with the problem that the gas molecules are packed very close together when the inlet flow enters the throat, whereas they are relatively far apart when they are discharged through the nozzle”, Kleijn explains. “The typical gas pressure of the inlet flow is three bar, but the exit pressure is something like 0.01 bar. The difference in pressure poses a problem for conventional flow simulations.” Conventional Computational Fluid Dynamics (or CFD), implemented in commercial simulation software treats the gas flow as a continuum. This means that the gas is no longer considered as a collection of separate molecules, but as a continuous medium, each point of which has a specific velocity, pressure, and temperature. At the microthruster inlet, the gas molecules are packed close enough together to allow CFD to be used, but the outlet flow is so thin that you cannot ignore the fact that it consists of separate molecules. Kleijn: “The crucial question at that point becomes which simulation technique you should use on the exit flow, and where you should separate one simulation method from the other.”

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Front view of the test model. The recess for the external valve with the nozzle is at the centre. Microsatellites consist mostly of a frame in which printed circuit boards are stacked. Space for the system was therefore at a premium, which is why it was decided to mount the gas generators next to each other. The casing containing the gas generators doubles as a buffer tank in which the gas is stored for later use.

In 2008 the T3mPS microthruster was selected to be demonstrated on the Delfin3Xt satellite. The original design has now been modified. This qualification model or prototype, with the nozzle at its centre, was designed and built in 2009. The external valve of the test model has been replaced with an internal device. The valve and the MST nozzle from the University of Twente have now been fitted inside the metal buffer tank. The cap on the left contains the sensors and their connectors. The connections of the gas generators have been moved to the rear of the unit.

The see-through CAD drawing clearly shows how the casing containing the gas generators, the sensors and the control valve doubles as a buffer tank. After launch a gas generator fills the buffer tank with nitrogen gas for the nozzle. Once the gas from the first

Particle simulation To simulate the nozzle flow, La Torre and Kleijn used a technique known as DSMC, or Discrete Simulation using the Monte Carlo method. This simulation technique uses a clever method to reduce the immense quantities of molecules to a manageable number (see text box for details). Together with TNO Science and Industry in Delft and Eindhoven, Kleijn’s group devised the X-stream DSMC code to solve this problem. Using the combination of CFD for the nitrogen inlet flow and DSMC for a major part of the outlet flow, La Torre and Kleijn looked at two problems. In the first place they wanted to find out how the rarefied nozzle flow affected the system’s thrust. The smaller a nozzle becomes, the more rarefied

gas generator has been used, the second generator is activated, etc. The electronic design has also been adapted To save weight, the casing and the eight gas

to meet the requirements of the

generators were built from pure titanium at

Delfi-n3Xt satellite. For instance,

the TNO-PML workshop. The required level of

the communication protocol was

miniaturisation entailed developing several new

changed from CAN-X bus to I²C bus.

production methods. These have been fully documented to make sure they remain available for future projects.

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The shape of the nozzle causes the nitrogen gas to accelerate to

the gas flow from the nozzle becomes, and the more important it becomes to find the answer to this question. In the second place they needed to know how the roughness of the nozzle’s walls affected thrust. A nozzle can never be perfectly smooth, and as it gets smaller, the effect of the walls’ roughness on the rocket’s performance was expected to increase.

supersonic speeds. The propellant gas enters the thruster through the converging section, reaching a speed of Mach 1 at the throat, the narrowest part of the passage. As the gas then enters the diverging section, it expands and accelerates further, leaving the nozzle at several times the speed of sound.

A number of test structures were made to determine the correct

Wall roughness To investigate the effect of the wall roughness, La Torre looked at both the circumferential and the longitudinal surface roughness of the nozzle. “As it turned out, the longitudinal roughness did not affect the thrust figures”, La Torre says, “and this is caused by the fact that the effective surface area of the flow aperture hardly changes. On the other hand, the circumferential roughness does have a marked effect, and can easily reduce the thrust by fifteen to twenty percent.” When considering the effect of the low density of the gas flow, the main question is how much the efficiency of the microthruster is reduced by increasingly smaller nozzle sizes, and consequently, lower thrust figures. For thrust figures in the low milliNewton to low microNewton range the efficiency is considerably reduced. This is caused by the fact that the area (the boundary layer) in which the

setting of the laser to obtain the right nozzle shape. In each instance a series of structures was made using the same settings. The silicon was then broken into pieces to assess the cross-section. Since silicon breaks along a crystal face, one of the breaks is sure to be right through the middle of one of the nozzles in the array.

Various stages during the production of a nozzle from silicon, as viewed through an electron microscope. To make the aperture, Ir Job Louwerse of the University of Twente used a femtosecond laser to work a 250 μm diameter surface according to a predefined pattern. The pattern was repeated 32 times for the first image, 64 times for the second image, 128 times for the third image, and 256 times for the last image. When silicon is treated with a femtosecond laser, micropillars are formed, creating the texture of the nozzle wall. The grooves in the

The cool gas generators are made of titanium and contain 0.3

walls are a remnant of these micropillars.

grammes of propellant. The two holes carry the electrodes for the electric ignition system. The small hole on the right is the outlet for the propellant gas.

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Main characteristics of the microthruster used on Delfi-n3Xt: • Thrust is provided by nitrogen gas generated in flight by small cool gas generators. The gas is stored in a buffer tank which doubles as the casing for the cool gas generators. The buffer tank is connected to the valve leading to the thruster. • The nozzle has a smallest diameter (the throat) of 100 and 250 micrometres. • The valve and the nozzle are manufactured using MEMS technology. • The thrust is between 1 and 100 milliNewtons. • The mass is less than 120 grammes. • It measures less than 90 × 96 × 35 millimetres.


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Bracket for the valve

Connector with 19 nozzles designed by Fernando Tardaguila and Barry

Discrete Simulation using the Monte Carlo method

Zandbergen of the TU Delft faculty of Aerospace Engineering and

(bottom) and nozzle of

manufactured especially by Dr Marcus Louwerse for testing

the qualification model of the microthruster.

at the Delft faculty of Aerospace Engineering. Each nozzle

For the next model

produces a thrust of only 5 mN, too little to be easily

The gas in the tiny microthruster still contains thousands of billions of molecules. These cannot all be simulated individually by even the largest existing computer. DSMC will therefore model the gas using a much lower number of particles. La Torre MSc and Professor Kleijn used between 100,000 and twenty million artificial particles. Each of these artificial particles represents a number of real gas molecules. The chances of any two particles colliding depend on the relative velocity of the two particles, the temperature, and the diameter of the particles. In addition there is a random factor, which is generated by the Monte Carlo method. It’s a bit like throwing dice to decide whether or not particles will collide.

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Dr Marcus Louwerse

measured using the means available at the time. This is why 19 nozzles were made in the silicon, producing

of the University of

an easily measured combined thrust of 95 mN. The

Twente is currently

silicon disc has been fused onto a glass tube. A metal

developing a silicon valve that will be

connector glued into the lower end of the glass tube is

integrated with the

screwed into the test rig.

nozzle.

The micropillar texture resulting from the femtosecond laser bombardment

bulk of the flow is affected by the wall, becomes relatively greater as the nozzle size decreases. La Torre: “On the other hand, this means that the angle of the nozzle aperture can be larger than dictated by the conventional design rules. After all, as the boundary layer thickness increases, the effective nozzle aperture decreases.” Although La Torre and Kleijn limited their research to microthrusters for microsatellites, the range of possible applications for microthruster systems is not limited to aerospace engineering, according to Berry Sanders of TNO Defence, Security & Safety. “If you’re analysing small quantities of gas or liquid in a lab-on-a-chip, you need a small pump system to move the fluid around. You don’t want your pump system to become much bigger than the chip itself. This is where the principles of microthruster systems could come in handy.” Glass nozzle TNO Defence, Security & Safety used the simulation results produced by La Torre and Kleijn to design the nozzle. Sanders: “The results enabled us to calculate the nozzle dimensions at which the thrust would become too low. Just to be on the safe

turned out to be less than ideal, and so Dr Louwerse created a nozzle with a much smoother wall at the centre of 6 mm

A number of test pieces were cut to assess the

diameter glass disc. The disc is fused onto

shape. The SEM view shows how nicely curved

a glass tube, which is then suspended by

Top view of the glass nozzle with the

the entrance to the nozzle is as a result of

means of O-rings and connected to the

nozzle shape at the centre (300 μm

allowing the glass to melt in a controlled manner.

propellant tank.

diameter).

represent groups of molecules and calculating their interaction using a probabilistic approach, Direct Simulation Monte Carlo (b). If we look at even more particles, it is better to abandon analysis altogether and (a)

(b)

(c)

estimate the probability of a particle being in a certain location with a

A fluid can be considered as a collection of particles (molecules) that

certain velocity (Boltzmann equation). Finally, if the distance between

interact as a result of short-distance and long-distance forces. In order

particles is very small relative to the size of the system (as determined

to be able to predict its behaviour, we must calculate the motions of

by the Knudsen number), only the macroscopic effects of the motions

each individual particle (a). This takes a fair amount of calculations,

(temperature, pressure, mean velocity, etc.) need to be considered.

as a gas real system, even a microscale one, contains a large number

In that case the fluid’s properties are described as a continuous field,

of molecules that all interact with each other. Simulating a large

with its behaviour determined by Navier-Stokes equations and solved

number of molecules can be simplified by considering particles that

using Computational Fluid Dynamics (CFD) (c).

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Molecular Dynamics The imaginary domain of the flow is divided up into small cells, each of which can contain dozens of particles. Looking at the behaviour of the particles inside the cells, you can then calculate macroscopic flow variables such as pressure, temperature and velocity. In Molecular Dynamics (MD), the movement of each and every gas molecule is simulated in a computer. DSMC is a practical alternative to MD, in which you model only a small fraction of the molecules. Theoretically, MD is the most accurate technique because it includes every gas molecule in the simulation. However, because of the immense number of molecules involved, calculations using MD take too much time to be of practical use for systems larger than a few nanometres. Even using DSMC for the entire domain of a micronozzle takes an enormous amount of calculation time, because the number

of molecules is already very large on the inflow side. The most practical solution therefore is to simulate the dense gas inlet flow using CFD, and to use DSMC for the main part of the nozzle flow, where the gas is rarefied. La Torre conducted full DSMC simulations for entire thruster system to validate the more practical and faster combined CFD/ DSMC. The full DSMC simulations took a month or two on a large parallel computer. Based on the comparison between full DSMC and combined CFD/DSMC, La Torre was able to determine the best place for separating the CFD and DSMC domains in order to optimise the simulation’s reliability versus calculation cost ratio. Thus he was able to obtain very accurate solutions in less than 10% of the calculation time needed for a full DSMC simulation.

side, we designed our thruster to stay well clear of that value.” It was decided to make the nozzle 525 micrometres long, which is the thickness of a standard silicon wafer as used for microchip manufacture. At its narrowest point − the throat − the system was to measure between 100 and 250 micrometres wide. The angles of the inlet section and outlet of the nozzle were to be between 15 and 20 degrees from the centre line. Based on this design, Marcus Louwerse of the University of Twente, who recently gained his doctorate, produced a number of nozzles. Nobody knew what the best technology was for producing such a minute nozzle. Nobody knew how to keep the surface smooth enough to prevent disrupting the gas flow. Louwerse started by trying out two different techniques: “First of all, my brother Job used a femtosecond laser to machine a piece of silicon into a nozzle. The femtosecond laser fires very short pulses at the silicon, causing the material to evaporate. When we looked at the result through an electron microscope, the surface of the walls turned out to be much too rough. Another drawback of this technique is that you have to create the inlet section from one side, and create the outlet section from the other side, which causes alignment problems.”

The flow inside the microthruster was simulated at the Multi Scale Physics department of TU Delft using a computer to see how the thrust efficiency is affected by the shape, size, and wall roughness of the nozzle. This figure shows cross-sections of three nozzles of different size: 3.6 × 7.8 mm, 0.12 × 0.26 mm, and 0.036 × 0.078 mm. The nominal thrusts are 1 N, 1 mN, and 0.1 mN, respectively. The velocity of the gas flow varies from Mach 0.3 (subsonic) at the inlet and the throat to about Mach 4 (supersonic) at the diverging section of the nozzle. The transition from subsonic to supersonic takes place at the throat. The wider the area with the high Mach number at the end of the nozzle, the higher the thrust. In the 1 N nozzle, the area with a Mach number above 4 almost reaches the walls, with only very thin boundary layers in which the velocity is reduced by friction. In the smaller nozzles the surface-to-volume ratio is much greater, with a lower Reynolds number, as a result of which the boundary layers are much thicker, considerably reducing the size of the high-velocity area. In the smallest nozzle Mach 4 isn’t even reached.

A second technique yielded better results. Louwerse now starts with a half-millimetre thick sheet of Borofloat glass instead of silicon. Using a technique called powder-blasting, he makes a small, 300 μm diameter, hole in the glass. He then raises the temperature of the glass to the point where it starts to reflow, allowing him to round off the inlet section of the nozzle with exactly the right curvature. “This process yields a much smoother wall than we got by laser treatment of silicon”, says Dr Louwerse: “Apart from the smoothness, the important thing is to get the nozzle perfectly symmetrical. If it weren’t it would be much more difficult to navigate the microsatellite in the right direction without causing it to spin. The melting process took care of that too. So, the microthruster fitted to Delfin3Xt will have a glass nozzle.” Funded by MicroNed, Dr Louwerse is currently working on a leak tight silicon valve for the thruster.

The effect of the wall roughness on nozzle flow and efficiency. The upper part of the figure shows Mach numbers for a nozzle with a nominal thrust of 1.14 mN and smooth walls. The lower part of the figure shows the flow in the same nozzle, but this time with a sinusoidal wall roughness with a 10 micrometre wavelength and a 4 micrometre amplitude, at right angles to the direction of flow. The wall roughness causes various parasitic weak shocks (as evidenced by the irregularities in the Mach number contours) and results in loss of energy and efficiency.

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Marketing Delfi-n3Xt will have to demonstrate that microsatellites can offer the same level of functionality as larger satellites. In addition to testing the thruster, Delfi-n3Xt will also have to show that it is capable of sending data back down to Earth at high transmission speeds.


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“Together with Sweden the Netherlands have managed to reach a leading position within Europe in the field of microsatellite propulsion”, project leader Berry Sanders says. “We hope that the Dutch industry will be able to sell our knowledge and skills in the future. We’re currently in discussion with Innovative Solutions In Space, a Delft-based company, about the right of use of the microthruster. Once we’ve cut a deal, they can start marketing the entire system.” These days, one in ten satellites is a microsatellite, and Sanders thinks the numbers will increase. “NASA is already using micro­ satellites for small scientific experiments. India has been adding five microsatellites to most of their space missions. Although micro­ satellites will never be able to completely replace large satellites, they are where the future’s going.” For more information, please contact:

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Reducing the nominal thrust. i.e. reducing the dimensions of nozzles, results in a lower Reynolds number and a higher surface-to-volume ratio. This results in thicker boundary layers and reduced efficiency of micronozzles. The 1 N nozzle still produces 98% of the theoretically achievable thrust, the 1 mN nozzle achieves 93% of the ideal value,

The engineering model of the thruster developed for the Delfi-n3Xt

and the 1 μN nozzle achieves only 75%.

satellite attached to the pivoted thrust arm of a (recently developed)

Ir Berry Sanders MBA, e-mail berry.sanders@tno.nl, or

50 mN thrust test bench with a measurement range of 2-50 mN. The

Prof. Dr Ir Chris Kleijn, e-mail c.r.kleijn@tudelft.nl, or

Hybrid simulation of the flow in a micronozzle with a nominal thrust

test bench is inside an industrial vacuum chamber, which was modfied

Dr Marcus Louwerse, e-mail m.c.louwerse@ewi.utwente.nl, or

of 25 μN. In the converging section of the system, the pressure

for this specific purpose by the Aerospace Engineering faculty of

Ir Barry Zandbergen, e-mail b.t.c.zandbergen@tudelft.nl.

and the density of the propellant gas are high, as a result of which

TU Delft. To avoid having to interrupt the tests when the cool gas

Internet: www.delfispace.nl.

the free space between the molecules is small relative to the

generators run out of propellant, a flexible tube (centre) is used to

dimensions of the nozzle. This means we can consider the gas as a

continuously feed nitrogen gas into the thruster’s buffer tank (upper

If the wall of a laser-cut hole is left

continuum, and simulate the flow using CFD. In the throat of the

right). The higher the thrust produced, the larger the deflection of the

untreated, micropillars are left by the

nozzle the gas expands with a shock to a much lower pressure and

rail at the thrust sensor (the brown box on the left).

process. By firing the laser repeatedly at

density. In this rarefied area the free space of the molecules has

the wall, the micropillars are removed

suddenly become large with respect to the nozzle dimensions, so we

and replaced by longitudinal grooves, as

can no longer consider the gas as a continuum. Therefore, the DSMC

shown in previous images. The concentric

method is used to calculate the motions of individual particles,

roughness reduces the nozzle’s efficiency.

which accurately reflect the behaviour of individual molecules in the rarefied gas. The CFD simulations in the converging section of the nozzle and the DSMC simulations in the diverging section meet

The effect of the

at a common interface, the optimum location of which depends on

longitudinal wall

the dimensions of the nozzle and the way in which it is operated.

roughness on the flow inside a nozzle.

La Torre and Kleijn found a criterion that can be used to accurately predict this optimum location in the throat.

Again, a sinusoidal roughness with a 10 micrometre wavelength and a 4 micrometre amplitude is being simulated, but this time the roughness runs parallel to the direction of flow. The effect

Results obtained with the test model of the microthruster fitted with the connector carrying 19 identical nozzles. Each nozzle is designed to generate a thrust of 5 mN at a buffer tank pressure of 2 bar. The figure shows the results

of such a longitudinal roughness was negligible, with no parasitic shock waves

of a test series in which the mass flow was varied in steps. The resulting thrust

occurring, and practically loss of efficiency.

and pressure in the buffer tank are also shown. The relationship between the mass flow and the changes in pressure and thrust can be clearly seen.

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Chapter 5 The MicroNed programme’s founders set out with an ambition: To establish a market-oriented, dynamic and sustainable public-private knowledge infrastructure on microsystems and to form a solid base for new product-market combinations. The founders were aware that only by focusing on core capabilities and by creating momentum, could regions achieve and maintain a leading position. The question that arises at the end of the MicroNed programme is whether that goal was achieved. We can best answer that question if we look at the goals in detail.

a | S et up of a dynamic, sustainable knowledge infrastructure in the area of Microsystem technology. The goal of MicroNed was to optimise the use of the existing infrastructure by creating mobility in R&D, and by generating an environment where cooperation and knowledge sharing would optimise each of the partners’ capabilities. That environment would have a culture of flexibility, adjusting itself to new developments and new opportunities. It would decidedly not be another institute or cleanroom. “Working closely together with other companies is becoming more essential than ever before, while the average size of the companies is decreasing. Participating in open networks is increasing in importance.” Kees Groeneveld, managing director of, FHI, a small technology branch organisation 136

When the programme started most of the collaborative activities in R&D were inside local expert communities, for instance a small start-up company together with a university or R&D activity in a large company with a university. Cleanrooms at the universities and large companies were mainly for internal use. As there was no MST research programme at a national level, no coordinated infrastructure existed. R&D projects as a rule were inflexible. An activity was planned for four years, a PhD student was trained on the job and adjustments to the plans were difficult. Whenever companies were involved, their role was predominantly on the sidelines. Once or twice a year the companies were asked for input and that was it. Activities with only few participants often lacked important expertise and expertise was only exchanged piecemeal. Project dynamics were more or less non-existent and there was barely any community building between the projects. This was not because people did not want to do differently, but it was built into the system and they had to abide by the rules. Inflexibility, absence of company involvement and lack of community building was clearly not creating the right circumstances for optimal exploitation of the MST capabilities of all the scientists and the private enterprises involved. This was especially true in the cases where products were being made by disruptive technology and especially where these products concerned new markets, for instance, microsatellites. “Microfluidics is a disruptive technology requiring major adjustments by its potential users. This will take time. Besides, it is characterised by its multi-disciplinarity.” Ronny van ‘t Oever, CTO Micronit BV.


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MicroNed Achievements MicroNed, therefore, initiated activities involving more than one university, and small companies cooperating with large ones. Extensive collaboration was encouraged, and the partners were allowed to propose alterations to plans and adjustments depending on the results and changing needs. To keep the programme mission up to date with the world of MST during its term of execution, research that appeared to be out of touch, was refocused or, in some cases, stopped. Besides these interventions, there was also a certain natural dynamic, in the form of a new partner that wanted to join, or partners that wanted to join another working group of MicroNed that suited their needs better, or partners that chose to stop participating in MicroNed. The organisation of MicroNed provided tools to handle these changes. In terms of numbers, these were substantial: approximately 150 project mutations took place, which involved about 9% of the total programme volume. Of these, 80% were a consequence of natural dynamics, and 20% a consequence of actions stipulated by the MicroNed management, following on from recommendations from external experts halfway through the programme. “MicroNed’s uniqueness is its orientation towards thinking in systems/solution, and also the active approach of small and medium-sized enterprises. The MicroNed management was not afraid of reconstructing work packages following requests from its participants.” Professor Cees van Rijn, CEO Aquamarijn BV The MicroNed consortium was composed of partners from various scientific and professional backgrounds,

each having its own community, drives, habits, codes of conduct and so on. The challenge for MicroNed was to unite these separate entities while keeping their individual strengths. The challenge will be to merge research organisations at different locations and/or to align research programmes at different locations within the Netherlands first in the framework of MicroNed and then within Europe.” Laurent Marchand, head of component engineering of the European Space Agency ESA / ESTEC Both scientists and representatives of commercial organisations acknowledge that by participating in MicroNed’s close collaboration, their mutual understanding of the other’s role and capabilities was enhanced. Over 150 work package meetings with the partners and interested users provided input and direction to the research activities. This led to stronger bonds and mutual relations and provided a fertile environment for setting up new initiatives. Interaction between different work packages in MicroNed was enabled by the clear and the fair arrangements concerning intellectual property (IP). After all, these decide how ownership and thus future benefits are to be distributed among the stakeholders. Clear arrangements had to be made to protect the legal and commercial position of all the parties involved especially in cases where one had to use one another’s knowledge and IP to generate new IP. In a programme like MicroNed where both SMEs and large industrial companies participate, trust is based on fair IP arrangements. Hence MicroNed defined the IP arrangements in such a way that it fitted the ambition

of an open and dynamic ecosystem. An important starting point was that parties within a programme granted each other the rights to their IP to conduct the research within the programme. During the execution of the programme new partners expressed their interest in joining MicroNed or staying close to see the outcome. A procedure for enrolment was defined by the board. For full partnership the Consortium Agreement had to be signed with the consent of all partners; users only needed to sign a non-disclosure agreement, MicroNed therefore was never a closed shop. It started with 32 active partners and ended up with over 60 partners and users, nearly 50 of them private enterprises (see Table 8: MicroNed users and partners). Most of them were taken on board the NanoNextNL programme, where the ecosystem concept was also embraced. MicroNed provided a substantial addition to the number of collaborations and projects between scientific institutes and private enterprises in the Netherlands. MicroNed started out with nineteen work packages, which resulted in nearly 160 new cooperative activities with industry. Besides these new industry-oriented collaborations and projects, about 200 academic partnerships and projects emerged in MicroNed. Several of the new projects have an international character. “In this sense MicroNed is organising Dutch MST research, enabling a process of intensive interaction and discussion among the participating organisations and contributing to a process of prioritisation, with the universities aligning themselves to the industries. The programme forces an evaluation of the 137


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research agendas and prohibits fragmented university research.” Kees Eijkel, Managing Director of Holding Technopolis Twente. If a project shows exceptional promise, an extra boost might cause the difference between successful continuation and it being shelved. So MicroNed initiated internal calls for short-term projects aiming at the exploitation of high potential activities (Auxiliary Projects). In 2008 and 2009 fourteen special projects received funding. The initiative was highly appreciated by the community. A substantial contribution to the creation of a dynamic MST community and network was the 2007 MicroNano Conference, jointly organised by MicroNed and MinacNed. This combined the MinacNed industry-oriented annual workshop with the more academic MicroNed Conference. The initiative grew into a yearly place to be for academics and industrialists working in MST. In 2008 NanoNed joined as well, adding a community more oriented towards nanotechnology. The conference evolved into a unique platform for presenting technology developments and is providing a fertile breeding ground for new cooperative ventures. In 2009 some 550 people from academia (65%) and industry (35%) attended the conference (in 2007: 300); about 10% were international visitors. The first issue of MicroMegazine was published in 2009. The science magazine aims at industrialists, academics, science journalists, opinion makers, civil servants and others interested in MST and innovation, publicising MicroNed’s successful outcomes like 138

projects with a commercial follow-up or those that have made a breakthrough. People within and outside the MicroNed community are greatly appreciative of the magazine while other popular (technical) magazines have often followed up with articles about MicroNed’s partners. As a whole the MicroNed community was very active in disseminating acquired knowledge. Altogether the community produced more than a thousand articles and presentations (see table 6: Scientific dissemination). This knowledge was also anchored in education, as will be explained more elaborately later on.

Conclusion 1: MicroNed brought the Dutch MST community closer together, creating new and sustainable partnerships between industry and academia. Flexibility in the execution of disruptive R&D programmes seems to be essential to ensure successful technology transfer in a dynamic community. Consequently the number of MicroNed’s industrial partners doubled. Both the MicroMegazine and the National Micro and Nano Conference were crucial instruments in creating a lively and interactive community. Many long-term partnerships were created, both national and international, while knowledge was anchored in education. The lessons learnt and the active MicroNed community were brought into the NanoNextNL programme.

B | S trengthen the fundamental and multidisciplinary knowledge in the area of microsystems along the whole value chain In the past products could be created straightforwardly. They were assembled from separately developed components, each part working in a single domain, such as an IC with a separate sensor. Such systems measure a single parameter, they are placed in a package providing mechanical strength and electrical interconnection. Today ICs require several integrated sensor functions, sensors that function in complex physical and (bio) chemical environments. Interconnections now also encompass fluidic and optical signals – the package has become an integral part of the design. As a consequence we now need semiconductor people understanding and speaking the language of biotechnologists and mechanical engineers capable of handling optical devices. Product specialists, scientists and engineers must understand one another’s drives and capabilities. They were brought together in MicroNed projects to encourage this to happen. For instance, the agricultural university at Wageningen and semiconductor company NXP may seem odd partners, but the copper surface of the NXP DNA sensors needs a specific organic coating which the department of Organic Chemistry at Wageningen University was able to deliver. But this sensor would be useless without a specific knowledge of diseases. The Royal Tropical Institute (KIT) in Amsterdam has this knowledge, transforming the sensor into a functional device. Even then, the results would have remained in the realm of exotic R&D without the drive of a company like NXP to turn them into a product. Complementary collaborations like these have created


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multi-disciplinary value chains that will last beyond MicroNed. A phenomenon that was not planned, but turned out to be a major achievement, was the emergence of new MST supply chains. Several of the initial MicroNed partners from industry ended up in one another’s small specialist supply chains, for example the micro fluidics supply chain: Micronit, Lionix, Bronkhorst, Demcon, Medspray, and Nanomi who later on formed the Microfluidics platform in MinacNed. This also allowed a cluster of smaller companies to act as one larger entity, offering a more complete solution. The same can be said of the Space cluster in MicroNed. To a lesser extent this was true of the modeling and fabrication clusters, where specific design and engineering tools for platform technology were being developed. Some of these tools, for modeling and manufacturing for instance, were successfully transferred to the more applicationoriented clusters. The optimisation tool used to calculate an optimal tube shape for the Coriolis sensor, or the tools used for the complicated interaction dynamics between multi nozzle systems for inkjet are good examples. “Application-oriented research is allowed as long as it fits into the platforms and can be potentially interesting for others in the programme. In general, MicroNed aims at creating the tooling that enables the application.” Wybren Jouwsma, founder of Bronkhorst High Tech BV Because of the pre-competitive nature of the MicroNed programme, the R&D was not finalised and several of the products in those budding supply

chains still need more of a boost for them to be developed. Several activities found a productionoriented follow-up in the High Tech Factory, a shared production facility at the University of Twente, funded by the Pieken-in-de-Delta programme. The High Tech Factory initiative aims at establishing a pilot production infrastructure for products based on microsystems and nanotechnology. Interestingly, this group has been extended by existing and more recently founded MST companies, such as Ostendum, Medimate, Smarttip, SolMateS and IMS. Four of them are OEMs and one is an established technology provider.

Conclusion 2: The R&D projects in the MicroNed programme were concentrated on complex MST systems, requiring multidisciplinary teams. Therefore scientists from various disciplines and high-tech companies were brought together in complementary project teams to learn from one another’s drive, challenges and jargon. The formation of specialised supply chains created new business opportunities. Partners of MicroNed completed the R&D network outside MicroNed with dedicated platforms (like the Microfluidics platform) and fabrication initiatives, which enlarged and reinforced the Dutch MST value chain.

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C|B  ridge the gap between lab innovation and commercial product Once a principle and its feasibility has been proved most academics tend to stop, leaving the seed to wither in a dry and barren pre-commercial desert, also nicknamed the ’valley of death’. Such a seed, however, needs fostering, shelter from rain and storm, watering and space to grow. That space is often missing in a commercial environment, especially when the right technology-application-market combination has not yet fully crystallised. Companies might sense its commercial potential, but they also realise it needs a couple more years of care to mature. During that phase industrial input and help is required to transform invention into innovative products. Through the dynamic community mentioned earlier, MicroNed provided an environment where such cases found shelter. Sometimes partners were deeply involved in the R&D activities, sometimes they were only involved as potential users. There are many examples of successful MicroNed projects in this book, such as the formation of droplets in inkjet printing with Océ, the micro dispensers for inhalers, the sun sensors and thrusters for microsatellites, the next generation micro reactors, the detection techniques for freshness in fruit and vegetables and for the early diagnosis of tuberculosis, to name but a few. Although we have chosen to publish the most advanced and successful projects in this book, many more projects remain invisible. Consequently, for various reasons, the potential of many of the MicroNed projects will remain unrevealed. Some of the successful MicroNed projects simply cannot be shown in full detail: the cases where companies discovered really 139


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interesting commercial opportunities were taken out of the MicroNed programme, because pre-commercial R&D is outside the scope of the MicroNed programme. In these cases MicroNed lost direct sight of the invention since it was to be incorporated in a protected industrial environment. A good example is the application of inkjet technology in the dairy industry, transformed into “milk jet” technology by FrieslandCampina and TNO Science & Industry, or the water filtration fibres of the University of Twente and Aquamarijn. Sometimes a MicroNed project is a part of a larger project. Take the TNO gripper for instance, as described in Chapter 3, where researchers at TNO Science & Industry dug into the problem of placing fragile MST components on a printed circuit board. They are building a new type of gripper which is expected to play a key role in the BlueBird project, a huge project for 3D chip assembly. In this case the full potential of the MicroNed project will only be known once the bigger project, of which it is a part, is successfully completed. And finally, some projects simply need some more time to flourish, within or outside MicroNed.

Conclusion 3: MicroNed created an environment in which mutual understanding between project partners from science and industry could evolve. It is this understanding that led to close collaborations. Because of this, inventions and newly developed products and processes did not remain at the research stage but took a step forward towards marketable products as this publication illustrates. Besides the successes, many projects in the MicroNed programme remain unrevealed for various reasons. 140

D | S et up and expand the amount of training and education in the area of microsystem technology MicroNed is proud to claim that over eighty young people were awarded a PhD for their research for the programme. They were not educated in just another technology, but also in a way of working which is more in line with the nature of MST where technology development is more multidisciplinary and where there fewer barriers between laboratory-factory or academia-industry. Several of the PhD recipients have already found a job in the industry, interestingly in many cases in companies not yet known for their interest in MST. Several of these PhD graduates are pursuing their academic careers in postdoc appointments at Dutch or foreign universities. Typifying the uptake of MST in university programmes are the ten new MST professorships that can be directly traced back to the MicroNed programme, (Table 7: New MST professors). They include not only MST trained academics, but also SME industrialists who are now (part time) university (associate) professors, examples being Professor Cees van Rijn, CEO of Aquamarijn and Dr Joost Lötters, Manager Development of Bronkhorst-High-Tech. So many of the results of MicroNed projects have been passed on in Bachelor and Master level courses, workshops and special education programmes, for example in the special course at the Hogeschool Zuyd polytech. the Micro Coriolis practicum at the University of Twente and the MEMS practicum at TU Delft. An honorary doctorate was awarded by TU Delft to Wybren Jouwsma, founder of Bronkhorst High-Tech BV, while Wageningen University awarded a personal

professorship to Dr Han Zuilhof. Furthermore, members of staff of Delft University and one from TNO accepted posts as lectors at Universities of Applied Sciences. MicroNed also acted as a magnet for international talent in the form of Professor Eberhard Gill, who came from the Deutsches Zentrum für Luft- und Raumfahr (DLR), or Professor Urs Staufer, who came from the École polytechnique fédérale de Lausanne (EPFL). Special mention should be made of the growing interest in MST from the Universities of Applied Sciences, as reported in an article about the use of microreactors by students at Hogeschool Zuyd in issue 4 of MicroMegazine, while issue 1 of the science magazine carried an article about students at Hogeschool Utrecht studying microsystems with one of the latest electron microscopes. Hogeschool Utrecht also participated successfully in one of the Auxiliary Projects.

Conclusion 4: MicroNed has had an important influence on training and education in the field of MST, not only for universities, but also for Universities of Applied Sciences. Some eighty PhDs were awarded, along with professorships and lectureships, hundreds of students were actively involved in bachelor as well as master programmes and the results of projects were disseminated and applied.


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E | C reate spin-off research MicroNed research projects started in many cases as explorative ventures. What is going to happen to these projects when MicroNed comes to an end? As explained earlier, the most successful projects left MicroNed early to be incorporated into industry (~10%), some projects stopped, either voluntarily or through a management decision (~15%), but most projects (75%) will now look for new funding opportunities and will go on to extend the various collaborations which have been formed during MicroNed in other settings. MicroNed, together with the industry, defined five key areas where it wanted to excel (MicroNed Industry Day October 2008). These key areas clearly show the natural interest groups in MicroNed, rather than the original matrix of MicroNed clusters. The end of the MicroNed programme will be a natural transition for most stakeholders involved. Numerous MicroNed partners are to participate in the NanoNextNL programme, arranged in a new and apparently more natural way. For instance, part of the space cluster will be embedded in the sensors and actuators programme in NanoNextNL. However, many MST space activities are planned outside NanoNextNL, with STW Assist for instance, and are being placed under the ambitious umbrella mission called Olfar. The mission, which has already attracted international attention, will be announced at the National Space Office (NSO) special meeting on the 29th October 2010 at ESTEC in Noordwijk. Other examples include the activities of the food processing industry, which mainly took place under the DSTI (Dutch Separation Technology Institute). The various related research activities within MicroNed

(such as encapsulation, fractionation and emulsification) will be incorporated in the related programmes of NanoNextNL, but backed up by a new institute, the Institute for Sustainable Processing Technology (ISPT). Thus, the overall trend is for MST technology challenges to be incorporated in NanoNextNL, the National Research Programme for Micro and Nano Technology. The created ecosystem is being brought together here, arranged in highly specialised groups. Special interest groups such as a space mission initiative, a micro-fluidics cluster or a food-processing cluster are embedded in other dedicated (industrial) platforms where they have their own dynamics and organisation and exist outside the boundaries of enabling technology programmes like MicroNed or NanoNextNL. Besides NanoNextNL, many new MST projects are being funded by EU-FP7, Smart Mix, Agentschap NL (SenterNovem), Pieken-in-de-Delta, STW, Point One (e.g. MEMSland), FOM, ESA and Nano4Vitality. In total more than 31 new projects have been reported by MicroNed partners (end of 2009 figures) with an estimated value in excess of 20 million euros.

Conclusion 5: The most successful MicroNed projects have been embraced by industry and have disappeared from MicroNedâ&#x20AC;&#x2122;s immediate supervision. A large part of the MicroNed community is now active in the NanoNextNL programme. The trend now is to face challenges related to micro and nano technology in the NanoNextNL programme, while dedicated (industrial) initiatives are finding their own organisation outside this national research programme.

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F|C  reate a basis for new commercial activities based on MST Manufacturing and processing have been important subjects for the MicroNed partners. We identified fourteen cases were MicroNed projects led to new processes or manufacturing technologies, (see Table 4: new or improved processes from MicroNed), eighteen new product ideas and ten improvements in existing products originating from the MicroNed programme, (see Table 3: New products from MicroNed and Table 5: Improved products from MicroNed). Some of the new products are still being developed in the academic realm. Nevertheless they have already found their way to MicroNed partners, users and other interested parties. Not all new products are suitable for adaptation by the existing partners. Another commercial trajectory is needed especially when a new product concept does not belong to any existing product range or when the product is disruptive for an existing supply chain. In such cases, starting up a spin-off company is a more viable commercialisation strategy. Such a diverse programme makes it difficult to calculate the exact contribution to the Dutch economy. However, MicroNed has contributed significantly to the creation of at least ten new companies, one of which has grown already into a 25+ employees company, (see Table 2: MicroNed spin-off companies). MicroNed has also contributed to the growth of several existing MST companies (for instance, LioniX and Micronit nearly doubled the number of employees) and MST activities within large companies.

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“I can only say that without MicroNed, there would not have been a Nanomi company. I would probably still be just one of the employees of a company.” Gert Veldhuis, CEO Nanomi BV Patents are often considered a good indicator of the success of a programme. However, this is not as simple as it seems. There can be sound economic reasons not to patent or to patent at a much later stage. Patenting an invention in an early (pre-commercial) phase is not always appealing or commercially interesting, while after filing many more years of development are often required to make a technology/product suitable for the market. Furthermore, filing a patent is only useful when a commercial follow-up is envisaged. During pre-competitive research, as in MicroNed, this is not a realistic expectation. Nevertheless eighteen patents were applied for during the execution of the programme, (see Table 1: Patents of the MicroNed programme). Surprisingly most of the patenting was in the area of electronics and sensors. Some areas are less suitable for patenting, like modeling / simulation and areas involving process and application development. Protection by trade secrets and company confidential process knowledge is a defence strategy more common to these industry segments. At first glance, there doesn’t appear to be a relationship between patented inventions and spin-offs, although most spin-off companies are based on unique core technology. Investigating this, it turned out that this was related to the long period it takes to mature new technology. Although MicroNed was influential, sometimes essential, for the start-ups, the creation of some of the companies was based on 142

pre-MicroNed research. This underpins the need for long-term research projects, which transform from fundamental research to more engineering oriented development. These findings also support the opinion that striving for as many patents as possible is not an effective strategy. From an economic perspective, it is not just the growth of the companies that is important, but also the change of focus towards products with a better value proposition. Some of our partners initially aimed at MST products and services with limited added value (a technology proposition). Near the end of the MicroNed programme those products are being offered with substantially more added value for supplier and customer, a service-based proposition. Interestingly, more economic deliverables came from SMEs than from large enterprises, underpinning the SME friendliness of the programme.

Conclusion 6: The MicroNed programme has led to a total of 32 developments relating to new MST products and processes. Some eighteen patents and ten spin-off companies directly originating from MicroNed played a role in the commercialisation process. Even though the research took place mostly at scientific institutes, participation of the industry has been essential, both in the R&D and for transformation from lab stage into pre-commercial products.

G | R ealisation of MST centre of gravity In a strictly geographic sense there is no such thing as a physical centre of gravity for MST in the Netherlands. There are various MST or MST related activities in the Netherlands ranging from national initiatives (such as Holst, Memsland and CTMM) to more local/ regional ones (like High Tech Factory, Dimes, or MiPlaza) or even individual research projects such as STW or NWO grants. All these initiatives have their own dynamics separate from MicroNed. However, from a world perspective the Netherlands as a whole can be regarded as a single region. For regions to be successful, cooperation and focus are essential. As explained before, the MicroNed programme therefore actively supported the formation of expert clusters within the Netherlands, often anchored in lasting platforms outside MicroNed. Worth mentioning are: the inkjet activities concentrated in Eindhoven/Venlo/ Enschede; the space community brought together in the MISAT cluster operating around Delft and held tightly together by new missions; the microfluidic cluster in the east of the country (initiated by MicroNed partners and anchored in MinacNed); the MST food cluster around Wageningen/Deventer; and finally the equipment cluster concentrated around Eindhoven, but reaching as far as Delft. More importantly, MicroNed is one of the founders of the new national micro and nano technology programme, NanoNext. This programme has specifically incorporated MicroNed’s ideas about the need for focus, the importance of cooperation between small and large industries and academia as well as the need for an active and dynamic ecosystem. It is expected that due to its sheer size and organisational form this government supported programme will


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become the centre of gravity for all micro and nano technology research activities in the Netherlands. One of the driving forces behind the clusters is the shared challenges and focus, often defined by MicroNed discussions and part of the post MicroNed follow-up research. Hence it is not surprising to see these clusters and their agendas back in the new NanoNextNL programme. “There is no simple alternative to carrying out our broad research agenda without participating in a broadly oriented programme tuned to the needs of the industry. Some part of it will have a more free explorative way of working others will be more structured and focused on solving well-defined problems. Organise these all around demand driven broad themes.” Marcel Pâques, Principle Scientist of FrieslandCampina

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Conclusion 7: There is no such thing as a physical centre of gravity for MST in the Netherlands. The MST activities and expertise are distributed over various initiatives, both national ones and more local/regional ones. Therefore MicroNed actively supported the formation of expert clusters and platforms, often regionally anchored. These expert clusters can also be found in the new national micro and nano technology programme, NanoNextNL, which is expected to become the centre of gravity for MST in the Netherlands.

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Chapter 6 Microsystem Technology in an international context The future of MST in the Netherlands very much depends on the driving forces in the industrial and commercial sectors. Initially it was safety in the automotive industry that gave the impetus to the global MST market. MEMS accelerometers and gyroscopes found their way into cars, for instance for ABS and airbag systems, followed by sensors for tyre pressure management. More recently, the same sensors have enabled new functionalities in games and mobile phones. The number of gyroscopes in phones is expected to rise from zero in 2009 to 26 million in 2010 and 285 million units in 2014. This development means that high-end cell phones will have to offer even more functionalities in the future, like barometric pressure sensors for determining altitude. Whereas initially such sensors had limited capability, being able to sense just one thing, modern sensors are multi-functional, combining multiple sensors in one package or on a single chip, as well as data processors and wireless communication subsystems. In the near future, energy harvesting will transform them into self-sustaining sensor systems, operating as stand-alone units or as a part of a network. Whatâ&#x20AC;&#x2122;s more MEMS microphones, RF MEMS components and small, integrated cameras are now all part of common (smart) portable electronic devices. MEMS, as this subsection of MST is named, now represents an eight billion dollar market, covered by about 150 companies worldwide. Sensor costs have significantly decreased over the years. So that one can now buy three axis accelerometers for a price considerably less then was paid for a single axis accelerometer a few years ago. The competitive and capital inten144


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Beyond MicroNed sive nature of this establishing market entails that it is dominated by semiconductor giants, like as Texas Instruments, HP and ST electronics. In MicroNed’s view, this is not a segment that will shape the future for MST in the Netherlands. Sensorification The appearance of MEMS sensors is part of a larger trend towards the ‘sensorification’ of the personal and professional environment. Solving specific problems frequently begins with measuring cause and effect. For instance, the concern that a gradual accumulation of small amounts of chemicals in drinking water or food may eventually damage our health has led to the development of ultrasensitive measurement tools. But smart sensors can also be used to facilitate interaction with our environment by sensing and anticipating our demand for light, temperature, etc. Ambient Assisted Living, as it is called, depends very much on sensors registering our presence, the temperature of a room etc. combined with intelligent systems. Besides needing sensors, individual equipment also needs to communicate. Imagine for instance climate control installations receiving weather forecasts, heavy energy consuming devices like washer dryers receiving up-to-date energy prices (smart grid). This ‘internet of things’ therefore will need microprocessors and communication functionality, actuators and so on. An interesting example is the Quake Catcher Network, which involved thousands of voluntary participants worldwide allowing the accelerometers in their laptop to constantly monitor earthquake activity. In places were sensors are needed, but where there is lack of land lines for electrical power and telecommu-

nications, wireless communication would be a solution, preferably along with energy harvesting functions, to overcome the need for frequent battery replacement. Energy harvesters use energy very efficiently through the limited amount of energy uptake. This in turn provides another push for miniaturisation, while smaller electronics in general lead to more energy efficient systems. Great challenges One should not forget that meeting the great challenges of the 21st century also provides a boost to sensorification and miniaturisation. Looming shortages of minerals, water and energy, increasing demands for health care, the fight against terrorism, energy conservation and environmental care in general are high on the political agendas. Microsystems are expected to play a crucial role here; we have already mentioned energy harvesters, saving on the use of energy. But sensors are also incorporated into smart grids, enabling delocalised generation of energy, and energy usage that is often carbon neutral and more evenly time-distributed. Explosive and toxin detection systems used in the fight against terrorism also use microsystem sensors. The ability to detect a diversity of (bio) chemicals, often in very low concentrations, is something only microsystems can enable. Health Care might be the most demanding application in terms of complexity, impact and reliability. Medical diagnostics in particular presents difficulties because of the complex media to be analysed. But the rewards are high. This market is expected to see the highest

growth figures of all in the coming years. But MST in Health Care is not just a question of more and better measurement. There is also a need for intelligent drug dosing, with mechanical pumps or through targeted chemical release. This will lead to less use of medicine, minimising of side effects and maximising of treatment efficiency. When such dosing mechanisms are coupled with diagnostic instruments, the loop is closed and optimisation can even go a step further. Surgical instruments for minimal invasive operations, prosthetics, electrodes for the treatment of Parkinson disease etc., are all enabled by MST. Many of these microsystems will rely on microfluidics to concentrate or pre-treat samples, to transport the samples to the sensors, to provide small doses accurately and in good time. The fast growing microfluidic market segment represents a 1.1 billion dollar market in itself and is expected to reach 3 billion dollars in 2014. Finally, health is also affected by nutrition, a dawning realisation that offers great potential for the Netherlands with its very strong food industry. Functional food can include smart additives that offer targeted nutrients to promote health and prevent illness, perhaps even on a personalised level. MST revolution Three aspects are important in the increasing role of microsystems in industry and in our daily life and need to be mentioned in order to give a clear understanding of the future of the MST industry: Technologies like microsystem technology and nanotechnology are disruptive by nature bringing about the break-up of old supply chains and the creation of new 145


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ones. Companies unable or unwilling to acquire new technological capabilities on time will succumb to the competition. Older generations of products and their supply chains might totally disappear. The demise of large scale industrial R&D and the advance of open innovation offers ample opportunities for entrepreneurial high tech companies to develop new products and processes and perform R&D services. The enabling properties of MST products and their economic consequences cause a snow-ball effect. The value chain of a MST based product is often like a pyramid upside down. Take for instance an accelerometer in the game console WII: the cost price is around one euro. It enables a consumer device with a selling price of around € 200, with accessories in the € 50 – € 200 range and software packages, of which several are sold per console, costing around € 50 a piece. Altogether the one-euro accelerometer enables the sales of several hundreds of euros of hardware and software. The same applies to inkjet heads or water filtration membranes. On top of these aspects specific to MST, we have to remember that developments in technology and markets are proceeding fast. Products appear and disappear seemingly overnight. We need flexibility, and more specifically adaptability. As to nanotechnology, interest remains as strong as ever, but is being manifest differently. The focus is sharper than in the case of MST and much more attention is being paid to how nanotechnology can be usefully and safely applied. One of the worries is the reluctance of Dutch companies to start working with nanotechnology. This may be caused by a hesitation to become involved in a sensitive public debate about safety and health, the lack of solid busi146

ness cases or by the huge investments involved in commercialising nanotechnology. MST could help to facilitate the debate by bridging the macro-nano gap. The lack of industrial scientists and engineers working on nanotechnology underpins the need for academic industrial cooperation in this domain. Small companies, too, could play a role here, being less vulnerable to public opinion. MST and the Dutch industrial landscape How will all this affect Dutch industry? The strong points of Dutch industry in general are its expertise and track record in equipment manufacturing, and its agricultural and process industry. Examples include microreactors for the chemical industry, micronozzles for spray drying and inhalers, microfluidic chips for miniaturised laboratories, sensors in equipment etc. Moreover Microsystem technology will specifically be an enabler for those products. Equipment companies already operating in the nano world, like FEI and ASML, are leaning on microtools and components. The Dutch industry has a strong position in microfluidics, a growth area providing not only enabling components for medical diagnostics, but also for analytical instruments, microreactors and other processing equipment like emulsificators. There are major opportunities for controlling processes better, and for making more complex ingredients and compounds, for instance, in the pharmaceutical industry. A particular strength of Dutch industry and academia is their willingness to cooperate on a basis of equality. This is a great asset, particularly in open innovation environments. In such circumstances specialisation and a flexible attitude towards market demands of the suppliers are essential.

Trends in the government, industry and academia triangle There are many ideas about how to promote innovation. They rank from “laissez-faire” (the Schumpeter approach) to industrial policy. However, there is consensus about the added value of dynamic clusters in the process of innovation. Those clusters can consist of more or less hierarchical organised structures led by large enterprises (the ASML supply chain being a good example), or cooperative activities between peers (e.g. the Dutch Devlab and Sensorclub). In the case of ASML the general direction of the R&D, dictated by the internationally accepted ITRS roadmap for semi conductors, is set out by the OEM and the subcontractors (often much smaller then the company in the lead) will follow. Organising an R&D activity together with a group of peers, without a dominating organisation in the lead, in a less stabilised product/market/technology environment is less straightforward. It needs an environment suited to flexible cooperation. How to facilitate such an environment and what framework is needed for that, is currently the subject of a great deal of discussion. Another innovation-related debate centres around the difference between universities and companies. The gap between the cherished “academic freedom” and the often single-minded drive for short-term results of the companies (especially small and medium-sized enterprises) is difficult to bridge. This is especially so if it is much more attractive and simple for academics to participate in long-term research projects or perform R&D work in cooperation with a large enterprise’s R&D organisation. This remains a potential threat for that part of the Dutch economy that is knowledge intensive, since collaboration and momentum are


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required to remain among the global top. Even though the Netherlands has excellent R&D and resources, this cannot compare in sheer size with the massive R&D programmes of the emerging Asian countries or with specific regions that create momentum by focusing on certain technology/product/market combinations. The Netherlands is very small compared to regions like Silicon Valley and some regions in Asia. On a global scale the Netherlands as a whole is a region comparable in size to North Rhine Westphalia in Germany. But the flip side is that while competition is global, so are the opportunities. To obtain and maintain the lead in specific areas we can build on our position as the worldâ&#x20AC;&#x2122;s seventh largest exporting country, with excellent infrastructure support, our strong agricultural sector and the accompanying process industry, as well as our expertise in equipment manufacturing,. The examples of (small) Dutch companies leading certain niche markets are numerous. We need to focus on our strong winning positions; we must adapt to the changing market environment. Focal point Determining what should become the focal points for concerted R&D action in the Netherlands will be a much-debated subject in the coming years. Real, new and often disruptive, technologies and product concepts, essential for economic growth, are often promoted by innovative SMEs and start-ups. Roadmapbased development for new generations of existing products is more the domain of large and established enterprises. Governments find it easier to listen to the harmonised voices of a few large companies, backed by solid market and employment figures, than to the cacophonic orchestra of entrepreneurs backed only by

their visions. SME-oriented development programmes will have to find their own place. When MicroNed started out it had a clear idea about its missions and goals. MicroNed wanted to establish a market-oriented, dynamic and sustainable publicprivate knowledge infrastructure for MEMS, to form a solid base for new product-market combinations. That original vision was fine-tuned during intensive discussions with industry leaders and companies midway through the MicroNed programme, resulting in a vision of the future of MST in the Netherlands: MicroNed Visie 2010. The report identified important (commercial) opportunities for microfluidic and sensor products, but also concluded that there was a need to address fundamental industrialisation issues. Opportunities & problems MST is a common term for a number of promising technologies or product combinations, mostly involving more or less straightforward MEMS components and more recently, complicated systems. Contrary to what would expect from the use of the term â&#x20AC;&#x153;systemâ&#x20AC;? in the acronym MEMS1, MEMS was primarily about components, mainly for the automotive industry. Nowadays, MST is much more multi-functional covering more diverse market segments. The major market segments are MEMS (for the automotive and consumer markets), followed by microfluidics (mainly for healthcare and analytics) and nanotechnology (instrumentation and materials taking the lead, but pharmaceuticals/healthcare following close behind). The point to be remembered is that nanotechnology is to a large extent enabled by microsystem 1 Micro Electro Mechanical Systems

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production and measurement instruments. Micro (and nano) technology innovations are slowly entering our daily life. Not so much in the form of grand schemes like Ambient Living, Internet of things or Smart Grid, but as small enablers like accelerometers in WII stations, actuators and sensors in portable medical devices, like insulin dosing equipment, and small sensors and actuators in our cars. These new enabling products are creating completely new value chains: new types of equipment are needed to apply MEMS layers, to structure microfluidic devices, to integrate smaller and smaller components into packages and to enable nanotechnology processing and measurement. Although the complexity of the micro and nano technologies and their applications seem to call for large, broadly oriented groups, results can only be achieved by ambitious and focused teams. To obtain a competitive national position one needs momentum; to make effective use of fast changing markets and technologies, one needs flexible organisations. Balancing these seemingly conflicting demands is the real challenge. The answer lies in the concept of an open ecosystem. Open Ecosystems In the past, large enterprises operating as Integrated Device Manufactures were able to create complete products in-house, requiring only the raw materials. The increasing number of different, specific scientific and engineering disciplines for each product, the speed of technological and market developments, the cost involved in maintaining large R&D organisations and inefficient production facilities, have resulted in the so-called Integrated Device Manufacturers no longer 147


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being cost-effective. Most of these large companies have therefore vanished or been transformed into head and tail organisations, concentrating on marketing and application-oriented R&D. They outsource as much as possible including fabrication and the development of components and subsystems. The concept of in-house R&D and production also inhibited the exploitation of many new ideas and technologies that did not fit into the strategy of the inventing organisation. Awareness of this led to open innovation being adopted by many of these organisations, not just electronic companies like Philips, but even the processing industry. The pharmaceutical industry in particular has become aware of the limitations of in-house research. Only a small number of their new products have their origin in the big companies and most are acquired elsewhere. This even goes for one of the biggest MEMS players: ST Microelectronics in Switzerland which had brought several products to market in cooperation with small companies. As a consequence, the future seems bright for multiorganisation, multi-disciplinary teams that are broad in technology scope and operate across the value chain to optimise development efforts and to shorten the time to market. These teams operate best with an equal status level for academics, industrialists, OEMs, component suppliers, process specialists, and providers of enabling technologies. Technology-based clusters or ecosystems are thus required, especially in areas where a multidisciplinary approach is needed, as in MST. MicroNedâ&#x20AC;&#x2122;s original vision was to create such an open and dynamic MicroNano ecosystem for organisations competing on a global scale. Far from having disappeared at the end of MicroNed, an even wider 148

community now supports such ecosystems since they carry the promise of added value for scientists as well as industrialists. For scientists they provide insight into the industrial problems to be worked on and offer support from industrial experts with specific expertise. For industrialists, they enable new products, processes to be screened and, last but not least, top talent to be recruited. This is a public private win-win situation. However, we need adaptability and room for dynamics in the development projects, not just to allow partners to switch from one part of the programme to another, but also to welcome new partners. The dynamics are especially needed in areas where technology developments are disruptive, i.e. where entire new products disturb existing supply chains and cooperation patterns. Focusing and clustering Some compare technology development with naval actions, of which there two kinds. The first one is a based on an organised fleet of ships-of-the-line under a unified leadership, following a pre-planned course, heading straight into the battlefield with massive force. The second is based on a fleet of independently operating ships, each of them flexibly exploring niche opportunities. Both strategies have their role and both aim for localised supremacy. The ASML supply chain can be compared to the shipof-the-line approach: roadmap-based development taking incremental, but challenging, steps resulting in a follow up of product generations. The strategy fits very well in more or less established product/market/ application combinations. The need for specific R&D and its potential economic value can be underpinned by market figures, the risks can be calculated, although

the investments involved are substantial. However, the number of Dutch large system suppliers is limited (ASML, ASMI, Philips Healthcare, OcĂŠ, FEI etc.) and they tend to transfer production (and R&D) to other countries as dictated by economics. Besides, these companies tend to be vulnerable to technology paradigm shifts (the invention of the transistor being an illustrative example). Niche markets or disruptive products are better served in a flexible setting. Here we often lack solid market figures and we must listen to people with a nose for paradigm shifts and to people with a mindset for following market developments: entrepreneurial professors and scientific entrepreneurs! The individual investments are often lower, but the risks are substantially higher. Developing sequential generations of products seemingly need road map based programmes and disruptive activities a more flexible setting, Governments are then faced with the questions: Do we give specific support to certain product/market/technology combinations (industrial policy)? Or do we restrict ourselves to facilitating innovation in a more general sense, with few restrictions on technology and applications? These are not necessarily contradictory, for both strategies share a need for an environment of companies (big and small) and universities with a shared technology interest and a (local) government that facilitates and/or promotes the venture. If paradigm shifts are identified and new technologies promise to create new opportunities, there should be room to explore them. However, at a certain point in time a choice will have to be made if the Dutch industry is to have an impact on the global landscape. Which niches fit and which donâ&#x20AC;&#x2122;t? Which areas are overcrowded and do not relate to our strengths, and where are the realistic opportunities?


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The MicroNed management was surprised to find that several of the large companies said that participating in the community was more important for them than the financial support for their own R&D. The MicroNed partners also expressed a strong willingness to operate in flexible and dynamic technology based ecosystems. There is a growing positive attitude for start-up companies, especially at universities. So we envisage a future for the Netherlands where small high tech companies explore market niches and participate in OEM supply chains, amongst others in the following areas: microfluidics, sensors and devices for medical diagnostics, laboratory and other equipment, and industrial processes for MST. Epilogue Well, that’s the end, at least for MicroNed, but not for MST in the Netherlands. MicroNed planted many seeds, it nurtured several young plants and it cared for several offshoots on older trees. MicroNed facilitated the emergence of new companies that bring new MST products and new technologies and for quite a few different markets and applications. Several large companies also made substantial progress towards renewing their products and technologies. These technologies have the potential to become platform technologies for several companies and several innovative products2. The programme was not only beneficial for companies, it also influenced the way universities work and the content of their educational programmes. Wageningen 2 Samenvatting MicroNed visie 2010+, kleine producten voor

succesvolle bedrijven. Richard van der Linde, Henne van Heeren, Fred van Keulen, November 2008

University brought their biochemical experts in contact with MST, in line with the general trend that research groups should become more multi-technology oriented. The faculties of the three technical universities disco­ vered the opportunities of MST, and will be introducing this technology into the world of mechatronic systems. On the other hand, the pioneers of MST learned to appreciate the values of sound engineering tools, such as modeling & simulation. The next generations of products will therefore be designed much more efficiently! And the discussion between nano and microtechnology? The awareness grew that there is more to win in working together than in competition. It is difficult to imagine nanotechnology without the handling and processing tools from the microworld. On the other hand, nanotechnology is providing an essential tool kit for microfluidic based sensors, catalysts in microreactors, etc. The joint forces in NanoNextNL will be the start of a united micronano approach.

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van Leeuwenhoek, (who can be regarded as the first microsystem scientist and engineer)! MicroNed also brought people together, creating added value and critical mass. The budding micro­ fluidica network in Twente for instance has grown into a national microfluidic cluster. Several of the MicroNed partners participate in this cluster. It has also enough momentum to attract ‘newbies’ in microtechnology. The annual Netherlands MicroNano Conference is another example of bringing people together; it gained momentum when MicroNed and MinacNed joint forces, getting another boost when NanoNed joined too. It has become the place to meet. So, the most lasting contribution of the MicroNed consortium might well be the creation of a micro (and nano) community. MicroNed triggered companies and universities to work with new partners, it taught those separate worlds to appreciate each other; and initiated bonds that will outlast the programme. It is in those bonds that the future of MST in the Netherlands lies.

Technology, although essential for the economic strength of a country like the Netherlands, is hard to develop in an environment that is traditionally oriented towards services, trade and financing (in 2002 just 19 per cent of the working population was employed in industry). It is therefore good news that recently the number of technical students increased again after several years of decline. The MicroNed consortium is also very glad that it provided Dutch universities and polytechnics with the essential microtechnology expertise to train this new generation of scientists. And, who knows, there might even be new microtechnology scientists among them of the calibre of Antonie 149


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Appendices

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Table 1: Patents from the MicroNed programme Patent

Patentnumber

Owner

Application

Albedo Insensitive Sunsensor

06075694.7

TNO

Agricultural

Remarks

Light sensor

06075693.9

TNO

Space

Multiple Apparature Battle Startracker (MABS)

06076878.5

TNO

Space

A method for making a glass supported system, such glass supported

08007746.4-2111

University of Twente

Process industry

Tailor-made functionalized silicon and/or germanium surfaces

PCT Int. Appl. (2005)

Wageningen University

Food & Health semiconductor

expanded 2006.08.30

Transmitter Receiver System

PCT/EP2008/067245

Delft University

Space & ICT

Also applications for EU and

Atomising device, atomising body and method of manufacturing the same

2009-002178

Medspray Xmems

Medical

Composition and fibrils from whey protein peptides

2001123

FrieslandCampina

Agricultural

Coriolis Flowsensor met optisch reflectieve bewegingssensor

EP2187184A1

University of Twente,

Semiconductor and similar industries

US2010122585A1

Bronkhorst

Stromingsmeetapparaat

1034905

Bronkhorst

Semiconductor and similar industries

Rotary connector for a rotating shank or axle

2002128

Delft University

Industrial

Assembly device relating to a placement device

WO 2008/156359/A1

TNO

Industrial

Placement device and assembly device comprising a placement device

EP07110562.1

TNO

Industrial

Method of making a product with a micro or nano size structure and

2007056

Aquamarijn

Water filtration

US2009237453

Oce

Printing industry

US 7,535,295 B1

Maxim Integrated Products

Electronic industry

system and the use of a glass supported system

USA patents

product Orifice plate for an ink-jet print-head and a method for manufacturing the orifice plate Chopper Stabilized Amplifiers combining low choppers noise and linear frequency characteristics Method for measuring a temperature, electromechanical device for

Inc. (USA) 2003431 in the Netherlands

Delft University

Life Science & Proces industry

2003643 in the Netherlands

Delft University

Life Science & Proces industry

measuring a temperature System and method for micro- and nanoelectromechanical sample mass measurement

152

Applied

sold to MTT


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Table 2: MicroNed spinoff companies Spin off company

Focus of activity

Website

Kryoz Technologies

Cryogenics; design, production and selling of micro cryocooler systems for specific, fully

www.kryoz.nl

integrated, stand-alone cryocooler systems, which can be used by our customer as a ‘cryogenic black box’. Since the cooler contains no mechanical moving parts, the system generates no vibrations and has a potential long life-time. ISIS

With miniaturization of electronics and breakthrough technologies from the IT-sector

www.isispace.nl

and consumer electronics, satellites and space based systems can be designed and developed in a different way. Nanomi Emulsification

Nanomi’s core technology is its proprietary microsieve™ emulsification process. The

Systems

microsieves™ are made by precise semi-conductor technology, which enables the

www.nanomi.com

production of highly monodisperse droplets and particles in a robust, reproducible and cost effective way. Innosieve Diagnostics

innovative diagnostic applications using nano/microtechnology-based microsieves in

www.innosieve.com

combination with LED-based optical photonic detection. Innosieve Diagnostics currently directs towards the development and sales of easy-to-use, micro/nanotechnology-based applications for the non-destructive detection of micro-organisms, eventually to even omit the use of enrichments. ChemTrix

Chemtrix (Geleen, NL) developed a little chip which is used for testing chemical

www.chemtrix.com

reactions. The advantages are: producing can be cheaper, safer and more sustainable and the development of farmaceutical chemicals can be done faster. Emultech

EmulTech, a contract development organization focusing on Advanced Drug Delivery

www.emultech.nl

Systems, provides solutions to the pharmaceutical and biotechnology industries through its proprietary Emulsion Technology for Micro Encapsulates (ET4ME). EmulTech currently offers clients tailor made enabling technology for the development and production of Advanced Drug Delivery Systems. Flowid

Microreactors are mainly used for organic synthesis of (im)miscible fluids (liquid & gas)

www.flowid.nl

that are extremely exothermic and fast, e.g. for the fine chemical and pharmaceutical industry. Innovative Data Services BV

a) The Automatic Identification System (AIS) is a ship-to-ship or ship-to-shore tracking

www.innovativedataservices.com

and communications system that provides information for surveillance and the safe navigation of ships, from which tracked messages indicating position and state information are sent. b) The strength of IDS’ space infrastructures lies in its numbers, employing many relatively simple, and thus low-cost, spacecraft to ensure the same capability and operational reliability as complex, large spacecraft.

HighFlux BV

Microfiltration with polymers

u.c.

Quintessentie

Fast track business development

www.qanbridge.nl

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Table 3: New products from MicroNed New product propositions

Main partners involved

Status

Electronics for wireless communication

TUD, NLR, Cosine

R&D

Coriolis sensor

Demcon, Bronkhorst, TUD, LioniX

Pre-industrial development

Leak tight microvalve

UT, Bronkhorst

R&D

Delfi interface bus

ISIS, Sytematic

Pre-industrial development

Micro sun sensor

TNO

Two patents applied for

Reconfigurable GPS receiver

Maxim

Licensed to USA company

Space-microcooler

Kryoz

Pre-industrial development by spinoff company

Gradiometer

UT, Shell, Fugro etc

R&D

Transmitter & receiver

TUD

Applied for patent

Microthruster

TNO

R&D

Medical inhaler

Medspray

Pre-industrial development

Nebulizers for parfum

Medspray

Discussion with potential users

Devices for encaptulation

Nanomi

Pre-industrial development

Lifescience chip (NXP)

NXP

R&D

Antibodies

WUR

Research

Freshness detection

WUR, TUD, Frieslandcampina

R&D

High speed gripper

TNO

Applied for patent

Extreme sensitive temperature sensor

TUD

R&D

New or improved processes

Main partners involved

Status

Sample preparation using Ultrasound

TUD, Aquamarijn, Philips

R&D

Industrialisation of encaptulates by upscaling

UT

Research

Haptic placement of CCD sensor

HU, Adimac

Pre-industrial development

Speed up of detection of tuberculosis with microdishes

KIT, MicroDish

R&D

Improved methods of finding oil from space

UT, Shell

R&D

Scanning of oilwells

Fugro, UT

R&D

Spraydrying

TNO, FrieslandCampina

Pre-industrial development

Spinning of protein fibrils

FrieslandCampina, WUR

Applied for patent

Encaptulation with fibrils

WUR, FrieslandCampina

Pre-industrial development

Chemical surface modification

WUR, NXP

Research

Packaging of electrical / fluidic / vacuum systems

Micronit

Pre-industrial development

Industrial production technologies for polymer production

Nanomi, TU/e, DPI

R&D

High speed milling for micro reactors

van Hoorn Carbide, Philips, Alliance

Pre-industrial development

Batch micro assembly

TUD, Memsland, Besi/Datacon

Pre-industrial development

Table 4: New or improved processes

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Table 5: Improved products Improvement of existing products

Main partners involved

Status

Optimal machine frame

ASML, TUD

R&D

Bus sensors vacuum environments

ASML

Pre-industrial development

Microreactor cooling

Kryoz

Research

Radiotelescope cooling

Kryoz

Pre-industrial development

GPS versterker koeling

Kryoz

Pre-industrial development

Architectuur Delfi NeXT

ISIS

Pre industrial development

Modeling& control distr. Systems

TUD, ESA

R&D

Anti-wetting for MEMS-inkjet

UT, Oce

R&D

Optimization simulation toolbox

TU/e

Open source

high speed coupling for micro turbines

MTT

patent sold

Table 6: Scientific dissemination Scientific dissemination Scientific presentations

490

Journal publications

152

Conference contributions

510

Contributions to books

18

Total scientific dissemination

1170

Table 7: New MST professors Person

From

To

Jacquelien Scherpen

Delft University

RUG (professor)

Harold van Brummelen

Delft University

TU/e (professor)

Joost Lรถtters

Bronkhorst High Tech

UT (professor)

Erik Puik

TNO

Lector MST Hogeschool Utrecht

Hans Langen

Delft University

Lector Avans Hogeschool Breda

Stefan Luding

Delft University

UT (professor)

Urs Staufer

EPFL

TUD (professor)

Rob Lammertink

UT

UT (professor)

Cees van Rijn

Aquamarijn

WUR (professor)

Eberhard Gill

Delft University

TUD (professor)

Wybren Jouwsma

Bronkhorst

TUD: Honorary Doctor

Han Zuilhof

WUR

Personal Professorate

Kofi Makinwa

Delft University

Anthony van Leeuwenhoek Professorate

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Table 8: Partners and users of the MicroNed programme Partners of MicroNed

Users of MicroNed

AkzoNobel

www.akzo-nobel.com

Adimec

www.adimec.com

Alliance

www.the-alliance.eu

Aeronamic

www.aeronamic.nl

AMC/UVA

www.amc.uva.nl

Bakker Magnetics

www.bakkermagnetics.com

Aquamarijn

www.microfiltration.nl

Bradford Engineering

www.bradford-space.com

ASML

www.asml.com

CCM

www.ccm.nl

Biomade

www.biomade.nl

Chemtrix

www.chemtrix.com

Bronkhorst High-Tech

www.bronkhorst.com

Contamac

www.werktuigbouw.nl

Cavendish Kinetics

www.cavendish-kinetics.com

ECN

www.ecn.nl

Chess Embedded

www.chess.nl

EFC

www.efcfiltration.com

Cosine Research

www.cosine.nl

Epcos

www.epcos.com

Demcon

www.demcon.nl

FlowID

www.flowid.nl

Eindhoven University of Technology

www.tue.nl

Fugro

www.fugro.com

Erasmus MC

www.erasmusmc.nl

FutureChemistry

www.futurechemistry.com

Femto

www.femto.nl

MA3 solutions

www.ma3solutions.com

FrieslandCampina

www.frieslandcampina.com

MEMS TC

www.memstc.com

Hogeschool Utrecht

www.hu.nl

MTT

www.mtt-eu.com

ISIS

www.isispace.nl

PDS Software

www.pdssoftware.com

Keygene

www.keygene.com

Philips Apptech

www.apptech.philips.com

KIT

www.kit.nl

Phoenix

www.phoenixbv.com

LioniX

www.lionixbv.nl

Physixfactor

www.physixfactor.com

Medspray

www.medspray.nl

Shell

www.shell.com

Micronit Microfluidics

www.micronit.com

Singulus

www.singulus.nl

Nanomi

www.nanomi.com

VDL-ETG

www.vdletg.com

NLR

www.nlr.nl

NXP

www.nxp.com

OcĂŠ

www.oce.com

Philips Research

www.philips.com

Plant research International

www.pri.wur.nl

RUG

www.rug.nl

Systematic Design

www.systematic.nl

TNO

www.tno.nl

TU Delft

www.tudelft.nl

TWMS

www.twms.nl

Unilever

www.unilever.nl

University of Twente

www.utwente.nl

van Hoorn Carbide

www.hoorn-carbide.com

Wageningen University

www.wageningenuniversity.nl

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