Effect of Eddy Currents on Method for Evaluating Shielding Performance of Magnetically Shielded Rooms Using Exciting Coil

The standard of Japan Electronics and Information Technology Industries Association EM-4502, in which the shielding factor (SFo) of magnetically shielded rooms (MSRs) for the uniform magnetic field can be estimated using coils within 10% error for the extremely low-frequency region of <;1 Hz without eddy current effects, has been already published. In this paper, to establish standard methods for evaluating SF for low-frequency region using coils, the effects of the setting method, size, and distance from MSR of the coils on SF are investigated by a linear eddy current analysis of an actual MSR made of copper and permalloy plates. It is shown that the coil should be placed in front of the door, and a much larger estimation error than 10% should be permitted for practical use in a standardization to estimate SFo for low frequency. Moreover, a method of estimating not only SFo but SFs as well when the noise source is close to MSR should be added in a standardization.