Electromagnetic shielding

Electromagnetic shielding is the process of limiting the coupling of an electromagnetic field between two locations. Typically it is applied to enclosures, separating electrical content from the 'outside world', and to cables, separating internal wires from the environment the cable runs through.

The shielding is achieved using a conductive material as a barrier. Typical materials include sheet metal, metal mesh, ionized gas, plasma and aluminum foil.

The shielding can reduce the coupling of radio waves, visible light, electromagnetic fields and electrostatic fields. The amount of reduction depends very much upon the material used, the method of connection of the shield (or screen) and the frequency of the fields of interest.

One example is a coaxial cable, which has electromagnetic shielding in the form of a wire mesh surrounding an inner core conductor. The shielding impedes the escape of any signal from the core conductor, and also signals from being added to the core conductor.

Some cables have two separate concentric screens, one connected at both ends, the other at one end only, to maximise shielding of both electromagnetic and electrostatic fields.