Lexicon Shielding

A shield is a metallic enclosure of a device, an assembly or a component to keep electrical interference away. Electric fields are kept away by the Faraday effect (Faraday cage), electromagnetic fields are attenuated. Magnetic fields are practically not affected.

For whole devices, a metal housing acts as a shield. Sometimes plastic housings are covered with a metal layer or a conductive coating to achieve the same effect. Wire netting can also occasionally be found as a shield. Cables are provided with shields made of wire mesh or metal foil, or combinations of these elements. It is always important that the shielding completely encloses the components or lines to be protected.

Shielding primarily acts on interference in higher frequency ranges, e.g. from radio waves. On the one hand, such interference is prevented from penetrating from the outside and possibly impairing the function of the device, but on the other hand, interference signals generated inside the device are also prevented from leaving the device. The latter is necessary so that a device meets the requirements regarding electromagnetic compatibility, which are specified in EU regulations, for example, and which must be complied with if a device is to be sold in the EU.

Shielding against low frequency magnetic fields (e.g. 50Hz) is hardly economically feasible, because large material thicknesses or special materials would be required (e.g. mumetal). A device or a line must therefore usually be immunized against such interference in some other way. In the case of cables, for example, twisting pairs of wires in symmetrical transmission.

See also:

• Wikipedia article [Shielding (electrical engineering)]