Electronic Environment #2.2015
To fully determine the electromagnetic susceptibility of a device, it is required to illuminate the device under test (DUT) from many different directions, especially if the DUT is large in relation to the wavelength P. F. Wilson, “Advances in Radiated EMC Measurment Techniques”, Radio Science Bulletin, No 311, December 2004, pp. 65-78., at every frequency using at least two polarizations. Figures 1 and 2 illustrate the importance of high resolution in both direction and frequency measurements. Figure 1 shows the results of a radiation susceptibility test in an anechoic chamber using 120 angles and two polarizations M. Höijer, M. Bäckström and J. Lorén, “Angular patterns in low level coupling measurements and in high level radiated susceptibility testing", in Proc. Int. Zurich Symp. Tech. Exhibition Electromagnetic Compatibility, Zürich, Switzerland, 18-20 August 2003. The test took 48 hours. The figure clearly shows that a slight change in angle of incidence can give a large change in the electromagnetic coupling into the object. Figure 2 shows the measured shielding effectiveness of a device M. Bäckström, K.G. Lövstrand, 2004, Susceptibility of electronic systems to high power microwaves: Summary of test experiences, IEEE Transactions on Electromagnetic Compatibility, Vol. 46, No. 3, August 2004, pp. 396 – 403.. As seen in the figure, a slight shift in frequency can give a large difference in shielding effectiveness. Thus, a test matrix that covers all directions as well as every frequency in a relevant frequency band will be very costly both in time and in test objects. Hence, a more efficient, but still relevant, test method is required. As an HPM weapon aims at achieving destructive effects, the system response will be non-linear and scaling from low-level coupling measurements or disturbance tests will not be possible. It follows that testing must be performed in the destructive non-linear regime. It should be noted that destructive HPM effects may be due to several different physical mechanisms, mainly related to either the absorbed electric energy or to the electric field strength J.H. Yee, W.J. Orvis, G.H. Khanaka, D.L: Lair, "Failure and Switching Mechanisms in Semiconductor P-N Junction devices", IEEE Power Electronics Specialists Conference, Albuquerque, NM, USA, 6 Jun 1983, pp. 154 - 159R. Blish, N. Durrant,
"Semiconductor Device Reliability Failure Models", International SEMATECH, Technology Transfer #00053955A-XFR, 2000D. M. Tasca, "Pulse Power Failure Modes in Semiconductors", IEEE Transactions on Nuclear Science, vol. 17, pp. 364-372, 1970.. For example, overvoltages can lead to a high-voltage dielectric breakdown or to surface inversion due to mobile ion contaminants. An electric breakdown can result in a current surge evaporating material. Induced voltages of the same order as the circuit operating voltage may lead to a temporary upset (nondestructive) J. Benford, J. Swegle and E. Schamiloglu, High power microwaves, 2nd ed., New York: Taylor & Francis (2007). Bursts of HPM pulses can result in cumulative effects eventually breaking a component. To find out exactly which mechanism is responsible for a particular equipment failure event can be challenging. It is usually not relevant from a practical point of view which destructive mechanism is achieved, but this has to be considered in HPM susceptibility testing. Another issue is component testing versus system testing. The Tasca curve can be expressed as the energy density required to destroy an integrated circuit as a function of the pulse length D. M. Tasca, "Pulse Power Failure Modes in Semiconductors", IEEE Transactions on Nuclear Science, vol. 17, pp. 364-372, 1970.. If the same component of a DUT is destroyed during a test series, the Tasca curve for the system will be related to the Tasca curve of that particular component. But if different components are destroyed at different illumination parameters, the Tasca curve of the system would be related to the envelope of the Tasca curves of different components. STANDARDS – HPEM ENVIRONMENT During the last decade several standards have emerged with descriptions of the HPEM environment relevant for the IEMI threat from HPM. IEC 61000-2-13 The International Electrotechnical Commission (IEC) in 2005 published the IEC 61000-2-13 standard with definitions of a "set of typical radiated and conducted HPEM environment waveforms that may be encountered in civil facilities" "Electromagnetic Compatibility (EMC) - Part 2-13: Environment - High-power electromagnetic (HPEM) environments - Radiated and conducted", IEC 61000-2-13, . In this document high-power conditions are considered to exist if the peak electric field exceeds 100 V/m. Both single pulse radiation and bursts of pulses are considered as threats. Examples of typical HPEM waveforms in the time and frequency domains as well as some examples of HPEM generators are given in annexes. The classification of HPEM sources in IEC 61000-2-13 is based on the spectral bandwidth. To include as many dif-
Table 1. Bandwidth classification of HPEM-sources "Electromagnetic Compatibility (EMC) - Part 2-13: Environment - High-power electromagnetic (HPEM) environments - Radiated and conducted", IEC 61000-2-13, .
Figure 1. Angular dependence of power picked up by a probe inside a DUT where the power is normalised against the external field power. The DUT is of the order of 1 m and has apertures. The test frequency is 4 GHz.
Band type
Percent bandwidth
Bandratio
Hypoband or narrowband
pbw ≤ 1 %
br ≤ 1.01
Mesoband
1 % ≤ pbw ≤ 100 %
1.01 < br ≤ 3
Sub-hyperband
100 % ≤ pbw ≤ 163.64 %
3 < br ≤10
Hyperband
163.64 % < pbw ≤ 200 %
br > 10
ferent HPEM sources as possible, it is recommended to select the low and high frequency limits (fl and fh) of emitted radiation pulses such that 90 % of the total pulse energy is contained within these limits. The standard gives a classification of HPEM sources based on bandwidth as given in Table 1, where the percent bandwidth, pbw, is defined as pwb = 100·2(fh-fl)/(fh+fl) and the bandratio, br, as br = fh/fl. Figure 2. The shielding effectiveness of a “radio equipment” DUT as a function of frequency. The five fixed test frequencies of the Swedish microwave test facility are shown as vertical dashed lines.
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The state-of-the-art generator systems considered in the IEC 61000-2-13 are found to have a field × range-product (rEfar) of at least 15 MV (hypoband and mesoband) or several MV (sub-hyperband and hyperband).
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