In EMC terms, the purpose of shielding is to isolate a volume (typically enclosing a product or system) from its electromagnetic environment. This involves attenuating electric and magnetic fields passing across the shielding boundary, which is generally a conducting barrier. Dealing with the electric field means presenting a low impedance to the field and ensuring that apertures in the barrier don't allow the field to pass through. Dealing with the magnetic component means allowing the barrier to carry an undistorted current flow so that a compensating magnetic field is set up, which cancels the original field. In both cases, a critical part of the shield design has to do with minimising the disruptive effect of breaks in the shield.

This section includes the following parts:

The theory of shielded enclosures

Practical treatment of apertures and seams

Use of conductive coatings and windows

Partitioning and zoning in shielded enclosures