Enhancement of EMP Shielding by Ferromagnetic Saturation

Although the subject of shielding by means of ferromagnetic materials has been investigated for almost four centuries, 1 it is not as well understood as the subject of shielding by means of nonferromagnetic materials. Many publications have dealt with magnetic shielding in both steady and time varying situations. Most of these papers are concerned with the calculations of shielding effectiveness for various configurations. To facilitate the computations, the permeability of the material is usually assumed to be a constant because without the aid of powerful digital computers the calculations would be impossible. In many cases the permeability chosen to represent the material is adjusted to make the calculations agree with experiment. Hence, in the past nearly all magnetic shielding problems have been treated as nonmagnetic shielding problems with the material permeability chosen greater than unity.