Common Shields Used In Cable Assemblies
There are several types of shields used. The more common shields used in cable assemblies are foil sheaths and metal braids. In specialty applications, shields can be made of conducting polymers.
Foil shields consist of a thin layer of metal, usually aluminum or copper which is attached to a carrier of some sort such as polyester. The polyester carrier provides strength and ruggedness that allows the foil to be wrapped around the cable without tearing or fracturing. A foil shield provides 100% coverage to the components it surrounds.
A braid shield consists of a woven mesh around a cable core. The mesh is made of strands of either bare or tinned copper wires, in certain applications a braid could be constructed of other materials such as silver plated copper or stainless steel. A metal braid provides a low-resistance path to ground and provides a much easier termination point than a foil shield. Terminations can be accomplished by either crimping /soldering the braid to the connector or with the assistance of a drain wire.
In wire and cable design the sole purpose of a shield is to bleed away any noise the cable is picking up. The shield of a cable and the way it is terminated must provide a path to ground.