Post by SOL Owner on Nov 20, 2013 10:34:17 GMT -6
An electromagnetic pulse is a burst of electromagnetic energy. It may occur in the form of a radiated, electric or magnetic pulse depending on the source. Electromagnetic pulse is commonly abbreviated EMP and pronounced by saying the letters separately (E-M-P). EMP is generally damaging to electronic equipment, and its management is an important branch of electromagnetic compatibility (EMC) engineering.
An electromagnetic pulse is a relatively short burst of electromagnetic energy over a spread of frequencies. Pulses are typically characterised by:
•The type of energy (radiated, electrical or magnetic) and amplitude
•The range of frequencies present.
•Pulse envelope or waveform, and amplitude.
Types
An electromagnetic pulse, EMP, also sometimes called transient disturbance, 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 victim. Some types are generated as repetitive and regular pulse trains.
Types of EMP divide broadly into natural, man-made and weapons effects.
Types of natural EMP event 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.
•Electrostatic discharge (ESD), as a result of two charged objects coming into close proximity or even contact. ESD events are characterised by high voltages of many kV but small currents and sometimes cause visible sparks. ESD is treated as a small, localised phenomenon, although technically a lightning flash is a very large ESD event. ESD can also be man-made, as in the shock received from a Van de Graaf generator.
Types of military EMP include:
•Nuclear electromagnetic pulse (NEMP), as a result of a nuclear explosion. A variant of this is the high altitude nuclear EMP (HEMP), which produces a pulse of a much larger amplitude and different characteristics due to interactions with the Earth's magnetic field.
•Non-nuclear electromagnetic pulse (NNEMP) weapons.
Types of (civilian) man-made EMP event also include:
•Switching action of electrical circuitry, including inductive loads such as relays, solenoids, or electric motors. Typically these send a pulse of voltage and/or current down any electrical connections present, as well as radiating a pulse of energy. The amplitude is usually small and the signal treated as "noise" or "interference".
•Continual switching actions of digital electronic circuitry.
•Electric motors can create a train of pulses as the internal electrical contacts rotate.
•Gasoline engine ignition systems can create a train of pulses as the spark plugs are energised.
•Power line surges. These can be up to several kilovolts, enough to damage electronic equipment that is insufficiently protected.
Frequency ranges
An EMP typically contains energy at 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, light, ultraviolet) and ionizing (X and gamma rays) ranges being excluded.
The highest frequencies are generated by NEMP bursts and continue up into the optical and ionizing ranges. Other types 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.
Pulse waveforms
The waveform of a pulse describes how its amplitude changes over time. Real pulses tend to be quite complicated, so simplified models are often used. Such a model is typically shown either as a diagram or as a mathematical equation.
Rectangular pulse
Double exponential pulse
Damped sinewave pulse
Most 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 may take the form of a rectangular or "square" pulse.
Lightning is unusual in that it typically has a preliminary "leader" discharge of low energy building up to the main pulse, which in turn may be followed at intervals by several smaller bursts.
EMP events usually induce a corresponding signal in the victim equipment, due to coupling between the source and victim. Coupling usually occurs most strongly over a relatively narrow frequency band, leading to a characteristic damped sine wave signal in the victim. 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.
learn more here en.wikipedia.org/wiki/Electromagnetic_pulse
An electromagnetic pulse is a relatively short burst of electromagnetic energy over a spread of frequencies. Pulses are typically characterised by:
•The type of energy (radiated, electrical or magnetic) and amplitude
•The range of frequencies present.
•Pulse envelope or waveform, and amplitude.
Types
An electromagnetic pulse, EMP, also sometimes called transient disturbance, 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 victim. Some types are generated as repetitive and regular pulse trains.
Types of EMP divide broadly into natural, man-made and weapons effects.
Types of natural EMP event 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.
•Electrostatic discharge (ESD), as a result of two charged objects coming into close proximity or even contact. ESD events are characterised by high voltages of many kV but small currents and sometimes cause visible sparks. ESD is treated as a small, localised phenomenon, although technically a lightning flash is a very large ESD event. ESD can also be man-made, as in the shock received from a Van de Graaf generator.
Types of military EMP include:
•Nuclear electromagnetic pulse (NEMP), as a result of a nuclear explosion. A variant of this is the high altitude nuclear EMP (HEMP), which produces a pulse of a much larger amplitude and different characteristics due to interactions with the Earth's magnetic field.
•Non-nuclear electromagnetic pulse (NNEMP) weapons.
Types of (civilian) man-made EMP event also include:
•Switching action of electrical circuitry, including inductive loads such as relays, solenoids, or electric motors. Typically these send a pulse of voltage and/or current down any electrical connections present, as well as radiating a pulse of energy. The amplitude is usually small and the signal treated as "noise" or "interference".
•Continual switching actions of digital electronic circuitry.
•Electric motors can create a train of pulses as the internal electrical contacts rotate.
•Gasoline engine ignition systems can create a train of pulses as the spark plugs are energised.
•Power line surges. These can be up to several kilovolts, enough to damage electronic equipment that is insufficiently protected.
Frequency ranges
An EMP typically contains energy at 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, light, ultraviolet) and ionizing (X and gamma rays) ranges being excluded.
The highest frequencies are generated by NEMP bursts and continue up into the optical and ionizing ranges. Other types 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.
Pulse waveforms
The waveform of a pulse describes how its amplitude changes over time. Real pulses tend to be quite complicated, so simplified models are often used. Such a model is typically shown either as a diagram or as a mathematical equation.
Rectangular pulse
Double exponential pulse
Damped sinewave pulse
Most 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 may take the form of a rectangular or "square" pulse.
Lightning is unusual in that it typically has a preliminary "leader" discharge of low energy building up to the main pulse, which in turn may be followed at intervals by several smaller bursts.
EMP events usually induce a corresponding signal in the victim equipment, due to coupling between the source and victim. Coupling usually occurs most strongly over a relatively narrow frequency band, leading to a characteristic damped sine wave signal in the victim. 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.
learn more here en.wikipedia.org/wiki/Electromagnetic_pulse