A simple model for minimizing source orientation dependence of finite width ELF magnetic field shields

The effectiveness of magnetic field shielding was studied. Possible health effects and the interference with the operation of CRT displays have resulted in a renewed interest in this subject. A simple analytic model for shielding by multiple layer, finite width planar shields was described. It was shown that the shielding effectiveness of single layer shields was greatly dependent upon the orientation of the source. A thin coating of magnetic material on a perfect electric conductor shield reduced this dependence. However, more than one thin coating did not improve the effectiveness of the shields with respect to leakage, particularly if the coating was very thin. It was shown that in all cases, there were regions of space where the shielding field was greater than the unshielded field. 8 refs., 10 figs