Magnetic Shielded Enclosure Design in the DC and VLF Region

A review of magnetic, shielding concepts and equations as applied to ideal shield configurations has provided a basis for the analysis of the shielding effectiveness of practical shielded enclosures to dc and VLF magnetic fields. The permeability of the shield material is considered as a function of the induction, and a significantly improved method of estimating the induction and permeability of the shield is presented. The effects of multiple shell geometry are given by the equations of this analysis, which are indeterminable with a transmission line analysis. The degrading effects of other departures from ideal shield materials and configurations are analyzed qualitatively; equations for estimating the magnitude of those effects are developed where possible.