The Explosive Magnetocumulative Generator or EMG is a relatively modern warhead developed as a non-lethal solution to knock out enemy electrical grids and communications systems.
The principle of the EMG is to send out a wide-band pulse of electromagnetic energy, which will be absorbed by surrounding electrical circuits. The sudden increase in potential is easily enough to destroy most electronic devices short of an electricity substation. The effect, known as Electromagnetic Pulse or EMP, was first discovered during the testing of thermonuclear weapons, when scientists wondered why their watches never worked after a test firing.
Obviously, the use of a nuclear weapon is slightly extreme to knock out some digital watches, so the EMG warhead was created. The EMG consists of one or several coils of copper wire, with many turns, surrounded by a ring or sphere of explosives shaped to produce a violent implosion. The coils are heavily charged with electrical energy, and the explosives are set off. The result is the coils themselves being 'squeezed' shortly before their inevitable destruction. The result is all the magnetic flux contained within the coils before the explosion is packed into a far smaller volume, which released an enormous blast of broad-spectrum EM radiation.
The EMG has not yet been deployed in a modern battlefield, although several delivery systems are fully developed should it be needed. The United States has developed a large EMG warhead for the Tomahawk cruise missile, and the Russians have openly completed work on two versions for their Spetznaz special forces teams. A grenade EMG, designed to knock out a single building, and a backpack version for darkening targets roughly the size of an airport.