Electromagnetic pulse
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This article is about the phenomenon in general. For nuclear EMP weapons, see Nuclear electromagnetic
pulse. For Earth magnetosphere pulsations, see Magnetic pulsations.
An electromagnetic pulse (EMP), also a transient electromagnetic disturbance (TED), is a brief burst
of electromagnetic energy. Depending upon the source, the origin of an EMP can be natural or artificial,
and can occur as an electromagnetic field, as an electric field, as a magnetic field, or as a
conducted electric current. The electromagnetic interference caused by an EMP disrupts
communications and damages electronic equipment; at higher levels of energy, an EMP such as
a lightning strike can physically damage objects such as buildings and aircraft. The management of EMP
effects is a branch of electromagnetic compatibility (EMC) engineering.
EMP weapons are designed to deliver the damaging effects of a high-energy EMP that will disrupt
unprotected infrastructure in the country,[1] thus the employment of an EMP weapon against a country is
the scenario of war most likely to collapse the functionality of the electrical network of the country. [2]
General characteristics[edit]
An electromagnetic pulse is a short surge of electromagnetic energy. Its short duration means that it will
be spread over a range of frequencies. Pulses are typically characterized by:
The mode of energy transfer (radiated, electric, magnetic or conducted).
The range or spectrum of frequencies present.
Pulse waveform: shape, duration and amplitude.
The frequency spectrum and the pulse waveform are interrelated via the Fourier transform which
describes how component waveforms may sum to the observed frequency spectrum.
Types of energy[edit]
Main article: Electromagnetism
EMP energy may be transferred in any of four forms:
Electric field
Magnetic field
Electromagnetic radiation
Electrical conduction
According to Maxwell's equations, a pulse of electric energy will always be accompanied by a pulse of
magnetic energy. In a typical pulse, either the electric or the magnetic form will dominate.
In general, radiation only acts over long distances, with the magnetic and electric fields acting over short
distances. There are a few exceptions, such as a solar magnetic flare.
, Frequency ranges[edit]
A pulse of electromagnetic energy typically comprises many frequencies from very low to some upper
limit depending on the source. The range defined as EMP, sometimes referred to as "DC to daylight",
excludes the highest frequencies comprising the optical (infrared, visible, ultraviolet) and ionizing (X and
gamma rays) ranges.
Some types of EMP events can leave an optical 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.
Pulse waveforms[edit]
The waveform of a pulse describes how its instantaneous amplitude (field strength or current) changes
over time. Real pulses tend to be quite complicated, so simplified models are often used. Such a model is
typically described either in a diagram or as a mathematical equation.
Rectangular pulse Double exponential pulse Damped sinewave pulse
Most electromagnetic pulses have a very sharp leading edge, building up quickly to their maximum level.
The classic model is a double-exponential curve which climbs steeply, quickly reaches a peak and then
decays more slowly. However, pulses from a controlled switching circuit often approximate the form of a
rectangular or "square" pulse.
EMP events usually induce a corresponding signal in the surrounding environment or material. Coupling
usually occurs most strongly over a relatively narrow frequency band, leading to a characteristic damped
sine wave. Visually it is shown as a high frequency sine wave growing and decaying within the longer-
lived envelope of the double-exponential curve. A damped sinewave typically has much lower energy and
a narrower frequency spread than the original pulse, due to the transfer characteristic of the coupling
mode. In practice, EMP test equipment often injects these damped sinewaves directly rather than
attempting to recreate the high-energy threat pulses.
In a pulse train, such as from a digital clock circuit, the waveform is repeated at regular intervals. A
single complete pulse cycle is sufficient to characterise such a regular, repetitive train.
Types[edit]
An EMP arises where the source emits a short-duration pulse of energy. The energy is usually broadband
by nature, although it often excites a relatively narrow-band damped sine wave response in the
surrounding environment. Some types are generated as repetitive and regular pulse trains.
Different types of EMP arise from natural, man-made, and weapons effects.
Types of natural EMP events include:
Lightning electromagnetic pulse (LEMP). The discharge is typically an initial huge current flow, at least
mega-amps, followed by a train of pulses of decreasing energy.
Jump to navigationJump to search
This article is about the phenomenon in general. For nuclear EMP weapons, see Nuclear electromagnetic
pulse. For Earth magnetosphere pulsations, see Magnetic pulsations.
An electromagnetic pulse (EMP), also a transient electromagnetic disturbance (TED), is a brief burst
of electromagnetic energy. Depending upon the source, the origin of an EMP can be natural or artificial,
and can occur as an electromagnetic field, as an electric field, as a magnetic field, or as a
conducted electric current. The electromagnetic interference caused by an EMP disrupts
communications and damages electronic equipment; at higher levels of energy, an EMP such as
a lightning strike can physically damage objects such as buildings and aircraft. The management of EMP
effects is a branch of electromagnetic compatibility (EMC) engineering.
EMP weapons are designed to deliver the damaging effects of a high-energy EMP that will disrupt
unprotected infrastructure in the country,[1] thus the employment of an EMP weapon against a country is
the scenario of war most likely to collapse the functionality of the electrical network of the country. [2]
General characteristics[edit]
An electromagnetic pulse is a short surge of electromagnetic energy. Its short duration means that it will
be spread over a range of frequencies. Pulses are typically characterized by:
The mode of energy transfer (radiated, electric, magnetic or conducted).
The range or spectrum of frequencies present.
Pulse waveform: shape, duration and amplitude.
The frequency spectrum and the pulse waveform are interrelated via the Fourier transform which
describes how component waveforms may sum to the observed frequency spectrum.
Types of energy[edit]
Main article: Electromagnetism
EMP energy may be transferred in any of four forms:
Electric field
Magnetic field
Electromagnetic radiation
Electrical conduction
According to Maxwell's equations, a pulse of electric energy will always be accompanied by a pulse of
magnetic energy. In a typical pulse, either the electric or the magnetic form will dominate.
In general, radiation only acts over long distances, with the magnetic and electric fields acting over short
distances. There are a few exceptions, such as a solar magnetic flare.
, Frequency ranges[edit]
A pulse of electromagnetic energy typically comprises many frequencies from very low to some upper
limit depending on the source. The range defined as EMP, sometimes referred to as "DC to daylight",
excludes the highest frequencies comprising the optical (infrared, visible, ultraviolet) and ionizing (X and
gamma rays) ranges.
Some types of EMP events can leave an optical 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.
Pulse waveforms[edit]
The waveform of a pulse describes how its instantaneous amplitude (field strength or current) changes
over time. Real pulses tend to be quite complicated, so simplified models are often used. Such a model is
typically described either in a diagram or as a mathematical equation.
Rectangular pulse Double exponential pulse Damped sinewave pulse
Most electromagnetic pulses have a very sharp leading edge, building up quickly to their maximum level.
The classic model is a double-exponential curve which climbs steeply, quickly reaches a peak and then
decays more slowly. However, pulses from a controlled switching circuit often approximate the form of a
rectangular or "square" pulse.
EMP events usually induce a corresponding signal in the surrounding environment or material. Coupling
usually occurs most strongly over a relatively narrow frequency band, leading to a characteristic damped
sine wave. Visually it is shown as a high frequency sine wave growing and decaying within the longer-
lived envelope of the double-exponential curve. A damped sinewave typically has much lower energy and
a narrower frequency spread than the original pulse, due to the transfer characteristic of the coupling
mode. In practice, EMP test equipment often injects these damped sinewaves directly rather than
attempting to recreate the high-energy threat pulses.
In a pulse train, such as from a digital clock circuit, the waveform is repeated at regular intervals. A
single complete pulse cycle is sufficient to characterise such a regular, repetitive train.
Types[edit]
An EMP arises where the source emits a short-duration pulse of energy. The energy is usually broadband
by nature, although it often excites a relatively narrow-band damped sine wave response in the
surrounding environment. Some types are generated as repetitive and regular pulse trains.
Different types of EMP arise from natural, man-made, and weapons effects.
Types of natural EMP events include:
Lightning electromagnetic pulse (LEMP). The discharge is typically an initial huge current flow, at least
mega-amps, followed by a train of pulses of decreasing energy.
