An Electromagnetic Pulse (EMP) is a short burst of electromagnetic energy that is generated when negatively charged electrons interact with a magnetic field. The pulse usually reaches its maximum value in about five nanoseconds and is halved in 200 nanoseconds. EMPs can occur at different altitudes, with those one mile or less above the Earth's surface known as Surface Burst EMPs (SBEMPs) and those found twenty miles above Earth referred to as High-Altitude EMPS (HEMPs). Most HEMPs fall within the frequency ranges of 100 kilohertz to 10 megahertz, and they can have several frequency ranges due to their short duration. The first man-made EMP was created in 1962 when a 1.4-megaton thermonuclear weapon was detonated 400 km above the Pacific Ocean.
The recovery time for small solar EMPs can range from days to weeks, while larger solar flares can take months to years to recover from. The effects of an EMP depend on its range, weather, ground connection, location, intensity, and length of the burst. The concept of a flow compression generator with explosive pumping to generate a non-nuclear EMP was first proposed by Andrei Sakharov in the Soviet Union in 1951. Natural electromagnetic pulses include lightning, coronal mass ejections (CMEs), and electrostatic discharges. The first recorded damage caused by an EMP was during the solar storm of August 1859, also known as the Carrington event. A High-Altitude Electromagnetic Pulse (HEMP) weapon is a Non-Nuclear Electromagnetic Pulse (NNEMP) warhead designed to detonate high above the Earth's surface. The National Cybersecurity and Communications Integration Center in Arlington has created guidelines to help federal, state and local officials and critical infrastructure owners and operators protect essential equipment from EMP threats.
According to Maxwell's equations, a pulse of electrical energy will always be accompanied by a pulse of magnetic energy. However, pulses from controlled switching circuits are usually roughly shaped like rectangular or square pulses. A pulse of electromagnetic energy typically comprises many frequencies, from a very low limit to an upper limit depending on the source. Induced pulses have much lower energy than threat pulses, making them more practical to create but less predictable. Electromagnetic shielding prevents electromagnetic waves from affecting sensitive electronic devices such as televisions, microwaves, mobile phones and baby monitors, as well as computer processors essential for today's smart devices.