Faraday Cage

A Faraday cage (or Faraday shield) is an enclosure formed by conductive material that blocks external electric fields. It is named after the English scientist Michael Faraday, who built one in 1836 to demonstrate that the interior of a charged conductor experiences no net electric field.

The operating principle is straightforward. When an external electric field reaches the conductor, free electrons in the metal redistribute themselves until the field they create inside the conductor exactly cancels the external field. The interior is shielded — but only as long as the conductor is sufficiently continuous and conductive.

For time-varying fields (radio waves), the same principle applies, with two qualifiers. First, the cage must be conductive enough that induced currents can flow freely. Second, any apertures (gaps, mesh openings, seams) must be small relative to the wavelength of interest. A common rule of thumb is that aperture sizes well below one-tenth of the wavelength provide significant attenuation; larger openings act as slot antennas and leak energy.

Faraday cages do not need to be solid. Wire mesh, woven conductive fabric, and perforated metal sheet all work, provided the apertures meet the wavelength criterion. The microwave oven door is a familiar example: a metal mesh with millimeter-scale holes that blocks 2.45 GHz microwaves (wavelength ≈ 12 cm) while remaining transparent to visible light.

Real-world applications include MRI rooms (which are built inside Faraday-shielded rooms to keep external RF out and the scanner's RF in), TEMPEST-rated secure facilities, anechoic chambers used for EMC testing, and shielded enclosures for sensitive electronics and broadcast equipment.

RADIHALT designs EMF protection blankets built around woven copper-nickel Faraday fabric. The terminology on this page — from Faraday-cage physics through attenuation figures and ICNIRP exposure limits — is what underpins the engineering and the claims we publish about our products.

We try to keep our marketing language tied to the same vocabulary regulators and physicists use. If a definition on this page conflicts with anything on a RADIHALT product page, the glossary entry is the source we hold ourselves to.