Prediction of magnetic shield plate performance using permeability in alternating micromagnetic fields

Magnetoencephalographs (MEGs) are highly sensitive to magnetic noises, and thus, a high performance magnetically shielded room (MSR) is essential. The shielding effect of a novel MSR should predicted to verify if it satisfies the required specifications of the MEG at the design stage. Therefore, an accurate prediction method based on the properties of shielding materials and shape of the MSR is necessary. We focused on the initial permeability μi of mu-metals which are generally used for MEGs; further, we proposed an estimation method for μi and a prediction method for the shielding effect using μi. To verify the prediction accuracy, we estimated μi of mu-metals and predicted the shielding effect of a plate, as simple examples, and compared the obtained result with experimental results. The comparison indicated that the prediction method can predict the shielding effect within approximate deviation of 8.2% for the plate even in a small magnetic field fluctuation region with a magnetic field as low as ΔH = 0.001 A/m. This result provided an important step necessary for predicting the magnetic shield effect of MSRs.