Faraday Cage

An electromagnetic field-blocking enclosure is called a Faraday cage or Faraday shield. Depending on the application, a Faraday shield can take the form of a continuous sheet of conductive material, or, in the case of a Faraday cage, it can be formed from a mesh of such materials. The Faraday cage takes its name from scientist Michael Faraday, who invented it in 1836.

In Faraday cages, electric charges in the cage’s conducting material are distributed in order to cancel out the field’s influence on the cage’s interior when it is exposed to an external electric field. Often during testing or alignment of the device, sensitive electronics (such as RF receivers) are protected from external radio frequency interference (RFI) by the use of this phenomenon. As well as protecting equipment and people from actual electric currents, such as lightning strikes and electrostatic discharges, enclosing cages also conduct current around the outside of the enclosed space while none passes through the interior.

Compass needles will still work inside Faraday cages since they can’t block magnetic fields that are stable or slowly varying, such as Earth’s magnetic field. When the conductor is thick enough and any holes are considerably smaller than the wavelength of the radiation, they shield the interior from external electromagnetic radiation. A screened room, for instance, can be used for certain computer forensic tests of electronic systems that require an environment free of electromagnetic interference. A metal mesh or perforated sheet metal completely encloses these rooms. A large amount of interference is blocked by the grounded metals which dissipate any electric current generated by the external electromagnetic field or by the internal electromagnetic field. EMF shielding is also an effective method of blocking interference. Despite their effectiveness in blocking EMP waves made by natural phenomena, trackers may be able to penetrate inside the cage (e.g., some cell phones operate at multiple radio frequencies so while one may not work, another will).

A Faraday cage dramatically attenuates or blocks radio waves that are received or transmitted by an antenna within it; however, the attenuation varies depending on wave form, frequency, distance, and power of the transmitter and receiver. Transmissions with high power and near-field range, such as HF RFID, are much more likely to penetrate. The fields attenuated by solid cages are generally broader in range than fields attenuated by mesh cages.

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