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January 2015 • The PCB Design Magazine 45 beyond design ELECTROMAgNETIC SuSCEPTIBILITY continues signers must be able to shape shielding materi- als to make various parts of the spacecraft. The material must protect the crew from radiation, and it must also deflect dangerous micromete- oroids. Fortunately, back down on Earth we are much safer from cosmic rays. Earth's atmo- sphere offers the same protection as a layer of concrete four meters thick. Incoming particles strike atoms in the atmosphere, producing an avalanche of protons and neutrons that in turn create a shower of millions of fragments—gam- ma rays, muons, neutrinos, electrons and other particles—that rain down over several square ki- lometers. Those reaching sea level are thought to be too weak to have any significant impact on electronic systems. Cosmic radiation intensity can also increase during periods of strong solar activity (flares), where masses of electrons, created by thunder- clouds, can produce bursts of radiation known as terrestrial gamma ray flashes. These flashes can pack more of a punch than cosmic rays and can dramatically affect aircraft electronics. The electronics industry has responded by developing a number of ways to combat the cosmic ray threat. The most common defense against soft errors is error-correcting software, typically involving check bits sent along with each packet of data, which is used to confirm that the contents have not been corrupted. In addition, multiple copies of data are stored in different locations in memory. In particular, vulnerable or critical systems like those on sat- ellites or aircraft have their complete hardware systems built in triplicate. Environments with high levels of ioniz- ing radiation create extraordinary design chal- lenges. A single charged particle can knock thousands of electrons loose, causing electronic noise and signal spikes. This is a particularly se- rious problem in the design of satellites, space- Figure 3: rAD hArD device (courtesy of Intersil).