Study on the Leakage Fields Prediction of a Static Ferromagnetic Shield in Consideration of Hysteresis and Residual Strain of Shielding Materials

A new approach for an estimation of a static ferromagnetic shielding effectiveness is proposed and verified considering the magnetic hysteresis of shielding materials. The measured leakage field of the shielding enclosure corresponds to the results of the finite element method (FEM) analysis when the permeability used for the calculation takes into consideration the effect of coercivity as a parameter representing the hysteresis of the shielding material. The effects of both permeability and coercivity on the leakage fields are discussed with regard to the magnetic properties of the shielding materials by using FEM analysis. The maximum leakage field, a figure of merit of the shielding efficacy, is determined by the coercivity of the material used for the shield. An increase in the leakage field caused by the deterioration of the soft magnetic properties is also discussed from the viewpoint of the effect of the residual strain induced during the assembly and installation of the shielding system. A double-layer shielding technique is effective in reducing the leakage field especially when it is feared that the shields are strained.