Low-Frequency Magnetic Shielding of a Double-Layered Planar Shield Against a Parallel Loop

This article theoretically investigates the shielding problem of a double-layered planar shield of infinite extent against the magnetic field generated by a circular loop placed parallel to the shield. First, Moser's formulation of solving the vector wave equation is extended to obtain the exact integral expressions of the shielded fields. Second, the approximate expressions are developed for electrically thick, nonmagnetic, metallic sheets. Also, the conditions to validate the approximate expressions are illimulated. Finally, the calculated results for the aluminum, the low-carbon steel and the permalloy are presented according to the NSA 94-106 setup. Meanwhile, the effects of thickness distribution and sheet-to-sheet spacing are analyzed.