An EMP (electromagnetic pulse) refers to short-term broadband electromagnetic radiation emitted in a one-off, high-energy compensation process. The compensation process means an energetic, highly excited system decays to the ground state by emitting an electromagnetic pulse. The causes for such events are usually electrostatic charging processes like thunderstorms or nuclear weapon explosions, but also occur within special electrical circuits. This process can be perceived as a flash of light in the visible spectrum.

EMP is not a periodic (i.e. pulsating) event but a transient process with the essential property of rising to a specific maximum value in a very short time and then falling comparatively slowly to the steady state value.

Are EMPs Dangerous?

Yes, EMPs are dangerous for electrical devices. The interaction of the low-frequency electromagnetic radiation components with free-charge carriers in metals and semiconductors induces strong, temporarily fluctuating currents. In electrical devices that are insufficiently shielded, this can lead to malfunctions, total failure or even the destruction of individual electronic components. 

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How Does an EMP Work?

To understand an EMP, we must first understand electromagnetism.

Electromagnetism is the creation of magnetic effects as a result of electrical currents. Moving electric charges are surrounded by magnetic fields, like the one depicted below.

EMP image of an electrical current moving through a coil to create a magnetic field
Electrical current moves through a coil and creates a magnetic field.| Image: Wikimedia Commons

Electric charges (like electrons) are the sources of electric fields. Magnetic fields, on the other hand, can be created in two ways:

  • Electric fields are created by moving electrical charges (electrical current).
  • Electric fields are created by electric fields that change over time.

Simultaneously, magnetic fields that change over time create electric fields. Therefore, these two fields are inextricably linked. 

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What Creates an EMP?

Electrostatic Discharges

During the spark discharge of electrostatically charged bodies, voltages and currents arise and combine with electric and magnetic fields. Together, they generate an electromagnetic pulse. Such discharges can damage or destroy electronic components.

 

Lightning (LEMP)

Lightning is a natural discharge in the atmosphere. The electromagnetic pulse triggered by the discharge and magnetic field is also called LEMP (lightning electromagnetic pulse).

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Nuclear Electromagnetic Pulse (NEMP)

A nuclear electromagnetic pulse (NEMP) is characterized by a rapid increase in intensity and reaches 90 percent of its maximum value within just four nanoseconds, which is much faster than an LEMP. 

An NEMP is triggered indirectly as a result of intense gamma radiation hundreds of kilometers above the earth’s atmosphere in connection with the earth’s atmospheric magnetic field by the so-called Compton effect. The Compton effect describes the scattering of a photon by a charged particle, which results in a decrease in energy (increase in wavelength) of the photon and a corresponding recoil of the scattering particle.

Due to high-energy gamma radiation in the range of a few MeV (kinetic energy of a few million moving electrons), a sudden ionization occurs on the molecules of the uppermost layers of the earth’s atmosphere. Electrons are knocked out of molecules (so-called primary electrons), of which a large proportion retain the original direction of the gamma quanta. These molecules change direction within denser layers of the atmosphere. 

Due to the high energy, some of these free electrons cause further impact ionization and thereby release more so-called secondary electrons. The negative electrons fly toward the earth and the remaining positive air ions form an electric dipole. The deflection of the moving charge carriers in the earth’s magnetic field creates a magnetic dipole.

This charge and current distribution of the dipoles in the upper layers of the atmosphere changes rapidly — both temporally and spatially. This creates a broadband, transient wave field. The actual electromagnetic impulse resulting from this wave field is responsible for the impairment of electronic devices and electrical systems.

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