What is cable shielding? And shielding hardware properties


#1

What is cable shielding?

Shielding involves placing a conductive surface around the circuit’s critical parts so that a combination of reflection and absorption attenuates the electromagnetic field that couples to it.

The shield provides a return path for the filtered currents and also guards against a direct field
coupling with the internal circuits and conductors.

If protection is required at low frequencies, the shield can be an all-metal enclosure, but if only high frequency (> 30MHz) protection is sufficient, a thin conductive plastic coating is sufficient.

Shielding Hardware:

Various materials are used for improving the conductivity of joints in conductive panels.

Gaskets and Contact Strip:

Gaskets and Contact Strip Shielding effectiveness can be improved by reducing the spacing of fasteners between different panels.

In these cases, it is possible to improve the conductive path between two panels or flanges by using any of the several brands of conductive gasket, knitted wire mesh or finger strips available.

These components are intended to be sandwiched between the mating surfaces in order to ensure continuous contact across the joint, so that the shielding current is not diverted.

Conductive Coatings

Conductively filled plastic composites can also be used to obtain a marginal degree of shielding (around 20 dB); It is debatable whether the extra material costs justify such an approach, given that conductive coating can offer better shielding performance.

Coating Properties

Environmental factors, especially resistance to abrasion and adhesion, are critical in choosing the right coating.

Major quality considerations for selecting coating are:

  • Will the coating peel or flake off into the electrical circuitry?

  • Will the shielding effectiveness be consistent from part to part?

  • Will the coating maintain its shielding effectiveness over the life of the product?