Screening effect of Ohmic and superconducting planar thin films

First are listed some analytic formulas which describe the screening properties of an infinite uniform planar thin film of an Ohmic conductor or a superconductor obeying London’s equations, interposed between an excitation loop or coil and a pickup of arbitrary geometry. Second, formulas are given for a thin, finite circular disk of ideal superconductor between small coils on or near its axis. Third, the film is adjacent to the small excitation coil and is subject to a field-independent (‘‘Bean’’) critical current density. Fourth, a numerical procedure is described for a circular disk screen which has a nonlinear non-Ohmic conductivity and a coaxial excitation coil. A formulation recently used by Brandt is obtained by splitting the screen into concentric rings and evaluating their self- and mutual inductances. © 1996 The American Physical Society.