An electromagnetic pulse (EMP), also sometimes called a transient electromagnetic disturbance, is a short burst of electromagnetic energy. Such a pulse may occur in the form of a radiated, electric or magnetic field or conducted electrical current depending on the source, and may be natural or man-made. The term "electromagnetic pulse" is commonly abbreviated to EMP, pronounced by saying the letters separately (E-M-P).
EMP interference is generally damaging to electronic equipment, and at higher energy levels a powerful EMP event such as a lightning strike can damage physical objects such as buildings and aircraft structures. The management of EMP effects is an important branch of electromagnetic compatibility (EMC) engineering. The damaging effects of high-energy EMP have been used to create EMP weapons. These are typically divided into nuclear and non-nuclear devices.
Such weapons, both real and fictional, have gained traction in popular culture.
An electromagnetic pulse is a relatively short burst of electromagnetic energy. Its shortness means that it will always be spread over a range of frequencies. Pulses are typically characterised by: The type of energy (radiated, electric, magnetic or conducted). The range or spectrum of frequencies present. Pulse waveform: shape, duration and amplitude. The last two of these, the frequency spectrum and the pulse waveform, are interrelated via the Fourier transform and may be seen as two different ways of describing the same pulse.
An EMP typically contains energy at many frequencies from DC (zero Hz) to some upper limit depending on the source. The whole range of concern is sometimes referred to as "DC to daylight", with optical (infrared, visible, ultraviolet) and ionizing (X and gamma rays) ranges usually being excluded. The highest frequencies are present in Nuclear EMP (NEMP) bursts. These continue up into the optical and ionizing ranges. Some types of EMP event can leave a visible trail, such as lightning and sparks, but these are side effects of the current flow through the air and are not part of the EMP itself.
|A National Airborne Operations CenterBoeing E-4 on |
EMP simulator HAGII-C for testing.
Minor EMP events, and especially pulse trains, cause low levels of electrical noise or interference which can affect the operation of susceptible devices. For example a common problem in the mid-twentieth century was the interference emitted by the ignition systems of gasoline engines, which caused radio sets to crackle and TV sets to show stripes on the screen. Laws had to be introduced to make vehicle manufacturers fit interference suppressors.
At a higher level an EMP can induce a spark, for example when fuelling a gasoline-engined vehicle. Such sparks have been known to cause fuel-air explosions and precautions must be taken to prevent them. A large EMP can induce high currents and voltages in the victim, damaging electrical equipment or disrupting its function.
A very large EMP event such as a lightning strike is also capable of damaging objects such as trees, buildings and aircraft directly, either through heating effects or the disruptive effects of the very large magnetic field generated by the current. An indirect effect can be electrical fires caused by heating.
These damaging effects have led to the introduction of EMP weapons. Most engineered structures and systems require some form of protection against lightning to be designed in.
From Wikipedia, the free encyclopedia.