Prediction of Cylindrical Magnetic Shielding Performance by Considering the Magnetic Field Strength Inside the Material

Magnetoencephalography (MEG) is highly sensitive to even a small amount of magnetic noise, and thus, a high-performance magnetically shielded room (MSR) is essential. The shielding effect of a novel MSR should be predicted to verify whether 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 the shape of the MSR is necessary. In this article, we proposed a prediction method using a simple formula and permeability measured against very small magnetic field fluctuations. Using a ring-shaped test piece, permeability was measured against a very small magnetic field corresponding to the Rayleigh region, and the initial permeability and Rayleigh constant were estimated to determine the permeability calculated by the formula. The magnetic field generated inside the material was estimated by magnetic analysis, and it was confirmed that the permeability of the Rayleigh region should be used in the formula. To verify the prediction accuracy, we examined a simple example of a cylindrical shell by comparing the calculated results with the experimental results. It was confirmed that the proposed method is