Zenpundit asked about electromagnetic pulse weapons and a basic description of how they work, so I hope this helps.
A growing concern relating to potential terror attacks on the U.S. is the use of Electromagnetic Pulse (EMP) weapons. EMPs were first observed in the 1940’s when a variety of atomic bomb tests were conducted. In order to understand, in a very basic way, how pulses of electromagnetic radiation are created, one needs to understand that, according to classical electromagnetic theory, electromagnetic radiation (which includes microwave, radio, infrared, visible light, ultraviolet, X-ray, and gamma radiations) is formed when charged particles are accelerated.
When an atomic bomb detonates, for example, whole nuclei of heavy atoms such as uranium and plutonium are literally ‘blown apart,’ and large amounts of charged particles (electrons and nuclear ions) as well as photons (‘particles of light,’ or pure electromagnetic energy) are produced. The charged particles are accelerated at very high rates, creating additional photons that can have high energies in the gamma ray region. The highest intensity occurs in a very short time period, the result of which is a sudden burst of electromagnetic energy, or pulse, that radiates outward from the detonation point.
Perhaps you already have experienced a ‘mini-EMP’ during lightning storms. A lightning bolt is a stream of electrons that is accelerated down from clouds, and some times your radio or television reception is momentarily disrupted due to lower level electromagnetic radiation produced by the accelerated electron stream. This gives one an idea of the effect EMPs may have on electronic equipment and infrastructure. If a power grid, transformer substation, power lines, satellites, airplane, radio transmitter, telecommunications centers, or anything electronic is irradiated with a high energy, high intensity EMP, not only can signals be disrupted but large induced electric currents (via electromagnetic induction) can form that physically damage the circuitry of the device. Especially vulnerable are microprocessors and any sort of computer chips, which are meant to work with small electric currents. Obviously, this is an amazingly dangerous class of weapons that could cause chaos on battlefields as well as in cities. And unlike nuclear weapons, EMP devices can, in principle, be made relatively easily and cheaply.
As one may expect, much interest in EMP weaponry has existed since WWII. It has been suggested that a substantial EMP weapon could be produced with some basic materials for a price of $400, and here lies a major threat since al Qaeda and other organizations or rogue nations would be able to afford and build them in large quantities. One design that would be relatively simple to build and cheap to produce is called a flux compression generator, where a tube of explosives is placed inside a coil of copper, and a bank of charged capacitors (devices that can store electric charge) provides energy for a magnetic field. When the explosives detonate at one end of the tube, one can imagine the magnetic field being compressed out of the other end of the tube, creating the pulse. There are other types of EMP bombs and devices that have been considered. For a detailed article on EMP weaponry and their consequences, see http://www.abovetopsecret.com/pages/ebomb.html.