Editing Electromagnetic shielding (section)

== How it works ==

{{See also|Faraday cage}}

Electromagnetic radiation consists of coupled [[electric field|electric]] and [[magnetic field|magnetic]] fields.  The electric field produces [[force]]s on the [[electric charge|charge]] carriers (i.e., [[electron]]s) within the conductor. As soon as an electric field is applied to the surface of an ideal conductor, it induces a [[current (electricity)|current]] that causes displacement of charge inside the conductor that cancels the applied field inside, at which point the current stops.

Similarly, ''varying'' [[magnetic field]]s generate [[eddy current]]s that act to cancel the applied magnetic field. (The conductor does not respond to static magnetic fields unless the conductor is moving relative to the magnetic field.) The result is that [[electromagnetic radiation]] is reflected from the surface of the conductor: internal fields stay inside, and external fields stay outside.

Several factors serve to limit the shielding capability of real RF shields. One is that, due to the [[electrical resistance]] of the conductor, the excited field does not completely cancel the incident field. Also, most conductors exhibit a [[ferromagnetism|ferromagnetic]] response to low-frequency magnetic fields,{{citation needed|date=April 2022}} so that such fields are not fully attenuated by the conductor. Any holes in the shield force current to flow around them, so that fields passing through the holes do not excite opposing electromagnetic fields. These effects reduce the field-reflecting capability of the shield.

In the case of high-[[frequency]] electromagnetic radiation, the above-mentioned adjustments take a non-negligible amount of time, yet any such radiation energy, as far as it is not reflected, is absorbed by the skin (unless it is extremely thin), so in this case there is no electromagnetic field inside either. This is one aspect of a greater phenomenon called the [[skin effect]]. A measure of the depth to which radiation can penetrate the shield is the so-called [[skin depth]].