Improvement in the Frequency Characteristics of RF Magnetic Shielding: Effects of the Superposition of Two Ferrite Plates over a BPSCCO Plate

A high-critical temperature superconductor (HTS) is ideal for use as an RF electromagnetic shield. As one of the basic areas of research for the improvement of the electromagnetic environment by the use of a bulk HTS as an electromagnetic shield, the present paper has applied a Bi-Pb-Sr-Ca-Cu-O (BPSCCO) plate to the far field region. In the frequency region from 1 to 30 MHz, however, the RF magnetic shielding degree SDH, with an average value of approximately 30 dB for the single BPSCCO plate, is not sufficient enough to shield electromagnetic waves. Accordingly, the present research has improved the frequency characteristics of SDH for the single BPSCCO plate to realize shielding over a broadband frequency region of 1 MHz to 3 GHz by the superposition of two ferrite plates over a BPSCCO plate; termed the sandwiched plate. The frequency characteristics of SDH for the sandwiched plate was improved by an average value of approximately 30 dB over the frequency region of 1 to 30 MHz. Experimental results revealed several characteristics of the sandwiched plate, which include the value of SDH as a function of radio frequency, and the non-dependence of SDH on the value of RF output power.