Evaluation method of shielding performance of cubic magnetically shielded room—simulation of magnetic field analysis with finite element method

Abstract

AbstractThe shielding factor of a large magnetically shielded room (MSR) cannot be measured by the usual methods. Successful results have been achieved by magnetic field analysis using the finite element method. Investigation of the shielding factor of an MSR included examination of: (1) a uniform magnetic field; (2) a magnetic field produced by an electric current flowing in a single circular coil (single‐coil field); and (3) a magnetic field produced by electric current flowing in a pair of Helmholtz coils (pair coil field).As a result, it was found that the shielding factor within MSRs varies with both the external magnetic field distribution condition and the position being measured within the MSR. The shielding factor at the center (when due to a uniform magnetic field) is lower than the shielding factor at the center when the field is produced by circular coils. The approximate equation expressing the ratio of the shielding factor due to the field of a circular current and that due to a uniform field using the center of the MSR as the measurement point was deduced as a function of the circular coil radius and its position. The method of evaluation of shielding performance of a cubic‐shaped MSR involves measuring the shielding factor due to the field produced by a circular coil and then transforming the results to yield the shielding factor for a uniform field. The approximate equation obtained thusly produces standardized shielding performance.