Energy, High energy, Light, Magnetism, Military

Electromagnetic pulse (EMP)

I received requests to write about electromagnetic pulse (EMP). In this post, are described the power of EMP, source, and weapons which use this technology.

How an electromagnetic pulse can damage?

An EMP is an explosion of strong electromagnetic waves with a large frequency band. When an electromagnetic wave is in contact with a conductor, occurs an induced voltage in the conductor. When higher the magnetic field’s variation, higher the induced electromotive force \varepsilon.

\varepsilon =-\frac{d\phi }{dt}

Higher induced voltage produces high current. An EMP can destroy power grids and telecommunication towers.

Transformer destroyed by electromagnetic pulse
A transformer from Quebec’s power grid, destroyed by EMP created by a solar storm in 1989. Source: Ask a prepper.

The excess of induced current in transformers causes saturation in the core, distorting the power grid’s waveform, creating harmonics. Consequently, the grid is destabilized with excess voltage, because safety relays are activated at the wrong time.

Voltage signals of a transformer with saturated nucleus. Source: All about circuits.

The majority of electronic devices can be damaged. Because these components operate with low current and voltage, like chips, transistors, and microprocessors. Especially if they are connected to power grid at the time.

The majority of cars will stop working due to dependence on electronic systems. Airplanes will be much more difficult to control and pacemakers will be shut down.

Artificial and natural sources of EMP

Coronal mass ejection

This phenomenon is produced by Sun. I have already written a post about the formation of coronal mass ejection. Click on the following button to read.

Coronal mass ejectionClick here

The plasma mass gets in contact with Earth’s magnetosphere, causing change on Earth’s magnetic field.

These changes in the magnetosphere produce a potential difference on Earth’s surface. Therefore, geomagnetic induced currents (GIC) appear in transmission lines through grounding, pipes underground, and railways.

Nuclear explosions

On July 9, 1962, the USA conducted an atmospheric nuclear test called “Starfish Prime”. An atomic bomb of 1.45 megatons exploded at 400 km above Johnston Atoll, in the Pacific Ocean.

Starfish Prime spot
Source: Space academy.

In Hawaii, at 1513 km far away, street lamps were destroyed, alarms were set off, telephone service was disrupted and the microwave telecommunication system was damaged.

Every nuclear explosion produces gamma rays, photons with very high energy. If an atomic bomb explodes above 40 km of altitude, gamma-ray enter the atmosphere and remove electrons of molecules that form the air. Free electrons follow a spiral trajectory with high speed. 

When a photon hits an electrons, happens the Compton effect

Compton Effect
Source: Wikibooks.
Compton scattering formula
Compton scattering formula. Source: Physics-Pelago.

Explaining the formula above:

  • \lambda_{f}: Wavelength of scattered photon.
  • \lambda_{i}: Wavelength of incident photon.
  • c: Speed of light in vacuum, which is 299,792,458 m/s.
  • m_{0}: Electron’s mass, whose value is 9.11\cdot 10^{-31}kg.
  • h: Planck constant, values 6,63\cdot 10^{-34}J\cdot s.

This equation tells us that higher the scatter angle, bigger the wavelength difference between incident and scattered photons. Scattered photons form the electromagnetic pulse, devastating electric and electronic systems.

electromagnetic pulse by high-altitude nuclear detonation

The e-bomb

It is possible to use a non-nuclear mean to generate an electromagnetic pulse. The e-bombs are bombs or missiles with a microwave generator and antenna in the warhead. These are supplied by batteries and coaxial capacitor bank.

bomb generator of electromagnetic pulse

This bomb uses the principle of Flux Compression Generation (FCG). Consist of a solenoid linked to capacitor bank, this solenoid involves a cylinder made of aluminum or copper, called armature. The explosive load is inside the cylinder.

Flux compression generator
Source: Wikiwand.

When the detonator linked to explosive is activated, the cylinder expands, creating a short-circuit with solenoid. The magnetic field created by solenoid is compressed, solenoid’s inductance is reduced and the load switch is opened. Sending a high current pulse to the antenna. An EMP of an e-bomb has a much smaller range than an atomic bomb exploding in the high atmosphere.

Liked it? Take a second to support Electrical e-Library on Patreon!

About Pedro Ney Stroski

Leave a Reply

Your email address will not be published. Required fields are marked *