Shielding

Shielding is the process of wrapping material around the outside of a wire or cable to provide two major functions: to act as a barrier to keep external signals from getting in and internal signals from getting out, and to serve as a part of the electrical circuit. A third function worth noting is the physical protection it provides the internal wire or cable. Shielding is normally specified as a cable construction detail. For example, the cable may be unshielded, contain shielded pairs, have an overall aluminum/mylar tape and drain wire or even a double shield. Shielding effectiveness is very complex to measure and depends on the data frequency within the cable and the precise shield design. A shield may be very effective in one frequency range, but a different frequency may require a completely different design. System designers often test complete cable assemblies or connected systems for shielding effectiveness.