EMP: Electromagnetic Pulse
From Network Dictionary Wiki
Electromagnetic Pulse (EMP) is caused by lightning and other high-energy phenomena. EMP is capable of coupling enough energy into unshielded conductors to destroy electronic devices.
In telecommunications and warfare, the term electromagnetic pulse (EMP) has the following meanings:
1.The electromagnetic radiation from an explosion (especially nuclear explosions) or an intensely fluctuating magnetic field caused by Compton-recoil electrons and photoelectrons from photons scattered in the materials of the electronic or explosive device or in a surrounding medium. The resulting electric and magnetic fields may couple with electrical/electronic systems to produce damaging current and voltage surges. See Electromagnetic bomb for details on the damages resulting to electronic devices. The effects are usually not noticeable beyond the blast radius unless the device is nuclear or specifically designed to produce an electromagnetic shockwave. 2.A broadband, high-intensity, short-duration burst of electromagnetic energy. In the case of a nuclear detonation or a meteor impact[1], the electromagnetic pulse consists of a continuous frequency spectrum. Most of the energy is distributed throughout the lower frequencies between 3 Hz and 30 kHz.
Source: from Federal Standard 1037C in support of MIL-STD-188 and from the Department of Defense Dictionary of Military and Associated Terms
In works of fiction, EMP has made many appearances, particularly in science fiction. In the cyberpunk sub-genre, EMP is often portrayed as a superweapon that distorts social order by destroying technological artifacts central to a society, or as a potent weapon against mechanical or robotic enemies. See Electromagnetic pulse in fiction.
Practical considerations
The mechanism for a 400 km high altitude burst EMP: gamma rays hit the atmosphere between 20-40 km altitude, ejecting electrons which are then deflected sideways by the earth's magnetic field. This makes the electrons radiate EMP over a massive area. Because of the curvature of earth's magnetic field over the USA, the maximum EMP occurs south of the detonation and the minimum occurs to the north.The worst of the pulse lasts for only a second, but any unprotected electrical equipment — and anything connected to electrical cables, which act as giant lightning rods or antennas — will be affected by the pulse. Older, vacuum tube (valve) based equipment is much less vulnerable to EMP; Soviet cold war era military aircraft often had avionics based on vacuum tubes. There are a number of websites that explore methods for protecting equipment in the home or business from the effects of an EMP attack.
It is important to note that many nuclear detonations have taken place using bombs dropped by aircraft. The aircraft that delivered the atomic weapons at Hiroshima and Nagasaki did not fall out of the sky due to damage to their electrical or electronic systems. This is simply because electrons (ejected from the air by gamma rays) are stopped quickly in normal (dense) air for bursts below 10 km, so they don't get a chance to be significantly deflected by the Earth's magnetic field (the deflection causes the powerful EMP seen in high altitude bursts), but it does point out the limited use of smaller burst altitudes for widespread EMP.
If the B-29 planes had been within the intense nuclear radiation zone when the bombs exploded over Hiroshima and Nagasaki, then they would have suffered effects from the charge separation (radial) EMP. But this only occurs within the severe blast radius for detonations below about 10 km altitude. EMP disruptions were suffered aboard KC-135 photographic aircraft flying 300 km from the 410 kt Bluegill and 410 kt Kingfish detonations (48 and 95 km burst altitude, respectively) in 1962 [2], but the vital aircraft electronics then were far less sophisticated than today and did not crash the aircraft.