Evaluation Method for Magnetic Shield Material using Incremental Permeability against Very Low Frequency Micro Magnetic Field Fluctuation

This is the authors' abstract. We don't add key points for this paper.

Magnetoencephalography (MEG) requires a magnetically shielded room (MSR) for protection against very slow and micro magnetic noise. An index called initial permeability, µi, is generally used to evaluate the performance of high-quality magnetic shielding materials. However, the measurement conditions, such as the magnetic strength and frequency of the µi, are not suitable for an MEG magnetic shield; further, the effect of background geomagnetism (DC magnetic field) is not considered. In this paper, we propose incremental permeability, µΔ, as an index to evaluate a magnetic shield for very low-frequency micro magnetic field fluctuations. In addition, the µΔ measurement system is described in detail. The measurement conditions of the magnetic strength and frequency were set at 1 to 0.001A/m and 3 Hz, respectively. We experimentally confirmed that geomagnetism does not have much influence on the measurement of µΔ. Lastly, the effectiveness of this evaluation method was demonstrated via results obtained for three different samples.