On simple methods for calculating ELF shielding of infinite planar shields

Simple approximate methods are developed and described for calculating the extremely low-frequency magnetic-shielding effectiveness for single- and double-layer infinite planar shields. In addition, exact expressions are given and "nearly exact" expressions are derived. Each expression has been compared to the exact expression in order to determine the range of parameters over which it is valid. Each approximate expression can be calculated rapidly and has a simple physical interpretation that leads to physical insight into the shielding process.