抄録
To shield magnetic noises, magnetically shielded rooms (MSRs) are used for biomagnetic measurements, etc. To evaluate the shielding factor SF, the magnetic noise is applied by coils. However, SFs depend on the size and position of the coils, so standard of JEITA EM-4502 evaluating SF for extremely low frequency region of less than 1 Hz without eddy current effects, in which the shielding factor SFo for the uniform magnetic field can be estimated by using coils within 10 % error, has been already published. Then, a standardization for low frequency region, e.g. 50 Hz, taking account of eddy current effects, is being discussed at present. In this paper, to establish standard methods for evaluating SF for low frequency region using coils, the effects of the eddy currents on SFs are investigated using a linear eddy current analysis of an actual MSR made of copper and permalloy plates.
