Low-frequency low-impedance electromagnetic shielding

The problem of low-frequency shielding of a loop that is axially perpendicular to a plane shield of infinite extent is analyzed by the thin shield work of S. Levy (1936), solution of the vector wave equation, and application of S.A. Schelkunoff´s (1934) transmission theory of shielding. Experimental data are obtained and compared with results of using the Levy and the Schelkunoff methods in the frequency range 100-50 kHz. The first analytical technique is not general, and the limits of applicability of the results are discussed. In the second solution, which is general, expressions are derived for the total electric and magnetic fields on both sides of and within the shield. The resulting expression for shielding effectiveness is shown to agree with experimental data. The final expression for shielding effectiveness shows independence of shielding with source-to-shield spacing, a results which is shown to be consistent with experimentally obtained data