直流磁界に対するシールドルームの遮蔽性能の検討

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The shielding effect (SE) of a magnetically shielded walk-in room (MSR) consisting of one or more layers of Permalloy for biomagnetism, testing of the spacecrafts and calibration of magnetometers, is often estimated using the Mager and Kalha (MK) formula. This was derived ideally, assuming closed continuous shells and did not take account of the existence of practical necessities such as holes, gaps and doors etc. and usually based on the assumption that each layer of Permalloy has a constant scalar permeability (µs) of about 30, 000. In this paper, 3-D static magnetic field analyses of the SE of cube type MSR’s composed of two layers and multiple layers and having a door, are described. The analyses are carried out by the finite element method and take account of the nonlinear magnetization property of Permalloy which was measured with using a ring sample. The following results are obtained. Firstly, the method of analysis is verified by comparing computed and measured results of the spatial magnetic field in MSR. Secondly, the relationship between the SE and the spacing between each layer, calculated by the 3-D magnetic field analysis, roughly agrees with that obtained by the MK formula, assuming µs of the two layers is a constant scalar. The µs of outer layer is higher than that of inner layer. Thirdly, in the case of the MSR of three and four layers, the calculated SE is smaller than that obtained using the MK formula. As µs depends on the amplitude of the magnetic flux density B, the µs of the outer layer is about 100, 000, which is much greater than 30, 000, but the µs of the inner layers is less than 60, 000. This indicates that the MSR of three and four layers actually consists of one layer of very high µs and the rest very low. This suggests that the discrepancy between the actual SE and the pre
社団法人電気学会の論文
2003-10-01

直流磁界に対するシールドルームの遮蔽性能の検討

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