大型零磁装置屏蔽系数的计算方法

For the facility to realize the nearly zero magnetic field, the shielding factor is hard to predicted accurately because of imperfect factors including edges, holes and airgaps, etc. A large-scale facility is composed of permalloy sheets with widths of a few meters and thicknesses of a few millimeters, and hence brings a challenge to meshing in finite element method (FEM) model. In this paper, the improved FEM methods are presented for shields in both DC field and AC field, using two types of interior boundaries to calculate the field changes because of the shield. It is demonstrated by the comparison with theoretical analysis of ideal shields. On the base of the improved FEM methods, the multilayer shield can be optimized efficiently and the influences of holes on the shielding factor can be analyzed. The presented calculation methods are applied to the new built magnetic shielded room (MSR) in technische universität München (TUM) and verified by the shielding factors measurement.