COUNTERMEASURES

While the EMP following a nuclear detonation would mostly be dangerous to electronic equipment in operation (for the wave travels mainly along the electric power network into the equipment if the "on" switch is closed), this type of microwave radiation can damage electronic equipment whether is in operation or not. Both US and Soviet equipment can now produce a peak power of 10 GW at a wavelength of 10cm wavelength, and about 1 GW at 1 cm (shorter wavelengths allow smaller dish antennas to form the beam, but are more difficult for the electronics producing high power). However, these weapons are subject to many inherent limitations, even if microwave technology progresses to higher power levels.

One of these limitations is the transparency of the atmosphere to microwaves: fog, rain and other precipitation will attenuate the radiation and eventually make it useless by scattering its energy out of the beam. This will not happen at the longer wavelengths, but the required antennas then become large, unwieldy and vulnerable.

There is also a natural limit to the power densities that can be achieved, because at high enough electric fields, the air ceases to insulate. (There would be no sparking arc discharges if that were not the case.) There are always free electrons in the air; when they are excited by the strong field in the beam, they will shock-ionize neighboring atoms, an avalanche effect will set in, and the electric field in the wave will be short-circuited. (However, since it takes a few nanoseconds to produce the avalanche effect, the process will only short-circuit the trailing edge of the traveling pulse. The lead-ing part of a few nanoseconds will "sneak through.")

More important, there are certain defenses against this new use of directed energy. The three basic measures are shielding (metal cladding that reflects the wave away), redundant circuits ("spare" circuits that take over automatically when their twins or multiplets are damaged), and "hardening" (using semiconductor chips whose operation is less vulnerable to high electric fields).

But the high field of the wave threatens damage not only by direct penetration. It can also induce high voltages and currents in conductors connected to sensitive subsystems, which will then be burned out. Such subsystems can be protected at their input port by frequency filters rejecting microwave frequencies, but passing on signals and power outside the danger band. Another possibility is using optical fibers for transmitting signals to subsystems. They do not conduct at microwave frequencies, so that the attacking pulse can induce no voltage in them.

[More (editorial): "No 'Runaway,' no cover-up at Savannah River," Wall St.J. 12/13/88 (also available in Fort Freedom's Power Plant); on nucl. weapons plants: AtE Dec 88; amounts spent by Swiss and US govts., Fed. Emergency Managm. Agncy. data quoted in Konzak Report (Box 18272, Denver, CO 80218), Jan. 1989; on Reagan's legacy: L.G. Crovitz, "How Reagan weakened the presidency," Commentary Sept. 1988 (synopsis in Fort Freedom's Commentary Tower); "How Congress erodes the power of the presidency," WSJ 2/6/89. Battle of Bulge: Simon & Schuster Encycl. of WWII; W.F. Weldon, "Pulsed power packs a punch," IEEE Spectrum, March 1985; H.K Florig, "The future battlefield: a blast of gigawatts?" IEEE Spectrum, March 1988; see also refer- ences given in the latter two articles.]