Design of soft-magnetic shield in electromagnetic tomography

Abstract In the electromagnetic tomography system, the soft-magnetic shield is employed to avoid external interference at low frequency. However, the influence of the soft-magnetic shield on the measurement lacks theoretical exploration, and the design of the soft-magnetic shield is arbitrary. To solve this problem, the effect of different thicknesses and locations of the soft-magnetic shield on the measurement is compared by numerical simulation. It is observed that the soft-magnetic shield not only enhances the boundary measurement data and sensitivity but also improves the quality and stability of the reconstructed images. The smaller the distance between the soft-magnetic shield and the pipe, or the bigger the thickness of the soft-magnetic shield, the better the improvement. The physical mechanism of the above results is explicated by the equivalent magnetic circuit analysis method. Based on the above investigation, the optimal structure of the soft-magnetic shield is designed, and it is verified by experiments.