Electromagnetic pulses (EMP) can be generated from a variety of sources, both natural and synthetic. Naturally occurring EMPs are usually caused by lightning, coronal mass ejections, and electrostatic discharges. Synthetic EMPs, on the other hand, are deliberately induced and can be created by nuclear or non-nuclear weapons. The concept of a flow compression generator with explosive pumping to generate a non-nuclear electromagnetic pulse was first proposed by Andrei Sakharov in the Soviet Union in 1951. According to Maxwell's equations, a pulse of electrical energy is always accompanied by a pulse of magnetic energy.
The first recorded damage caused by an EMP was the solar storm of August 1859, also known as the Carrington event. To achieve the desired frequency characteristics for optimal coupling to the target, wave-forming circuits or microwave generators are used between the pulse source and the antenna. These usually send a pulse to any electrical connection present, in addition to radiating a pulse of energy. A high-altitude electromagnetic pulse (HEMP) weapon is a NEMP warhead designed to detonate high above the Earth's surface.
An EMP typically comprises many frequencies, from a very low limit to an upper limit, depending on the source. Most EMPs have a very sharp edge of attack and build up quickly to their maximum level. Induced pulses have much lower energy than threat pulses, so they are more practical to create but less predictable. The pulses of a controlled switching circuit are usually roughly shaped like a rectangular or square pulse.