Lexikon Abschirmung specifications

Category : Lexicon

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

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

Shielding primarily affects interference in higher frequency ranges, e.g. due to radio waves. On the one hand, such disturbances are prevented from penetrating from the outside and possibly impairing the function of the device, but on the other hand, interference signals arising in the device are also prevented from leaving the device. The latter is necessary for a device to meet the requirements regarding electromagnetic compatibility, which are e.g. specified in EU regulations, and which must be complied with if you want to sell a device 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 disorders in a different way. In the case of cables, for example, the twisting of wire pairs with symmetrical transmission is suitable for this purpose.