1. How a Shield Works
A shield contains or excludes electromagnetic energy by reflecting or absorbing the energy.
Whenever EM energy passes from one medium into another, a portion is reflected, just like light off the surface of water. The energy not reflected at the shield’s surface goes into the shield.
Whenever EM energy passes through a conductive material (shield), some of it is absorbed. Absorption occurs in the shield.
A very small amount of EM energy does not get reflected or absorbed. This is the transmitted energy.