2000s AFOSR-Funded Research Leads to New Type of Artificial Muscle (2005-present) Dr. Ray Baughman, director of the NanoTech Institute at the University of Texas, Dallas, and his team of researchers have been working on artificial muscles for more than 20 years. This pioneering work stems from an exploratory research program supported by AFOSR Program Manager Dr. Byung-Lip “Les” Lee since 2005, whereby the team invented many new muscle types, including electrochemical carbon nanotube and conducting polymer muscles, as well fuel-powered muscles. The latter, powered chemically by alcohol or hydrogen, operate similarly to natural muscles, but they are limited in that they cannot function at extreme temperatures and have low efficiencies for energy conversion. Baughman’s nano-based muscles, which are 30 times stronger than natural muscles, are made of very thin sheets of nanotubes (1/10,000th of the diameter of a human hair) that on a weight basis are “strong as steel” in one direction and as elastic as rubber in two other directions. These artificial muscles can also operate at extreme temperatures, which makes them especially attractive for space applications. They are also being viewed as a means for endowing soldiers with super-human strength through the use of exoskeletons. Artificial muscles may also be used to actuate “smart skins,” which
would give Air Force aircraft the ability to change their appearance. “We want to use the carbon nanotube sheets to affect the boundary layers on Air Force micro air vehicles and even larger vehicles to provide a new type of controlability and increase flight efficiency,” Baughman said. The most recent research by Baughman and his international team from Australia, China, South Korea, Canada, and Brazil has resulted in new artificial muscles made from nanotech yarns and infused with paraffin wax can that can lift more than 100,000 times their own weight and generate 85 times more mechanical power during contraction than the same size natural muscle. The new artificial muscles are made by infiltrating a volume-changing “guest,” such as the paraffin wax used for candles, into twisted yarn made of carbon nanotubes. Heating the wax-filled yarn, either electrically or using a flash of light, causes the wax to expand, the yarn volume to increase, and the yarn length to contract. “Because of their simplicity and high performance, these yarn muscles could be used for such diverse applications as robots, catheters for minimally invasive surgery, micromotors, mixers for microfluidic circuits, tunable optical systems, microvalves, positioners, and even toys,” Baughman said.113
97