Role of magnetic materials in power frequency shielding: numerical analysis and experiments

Shielding of magnetic fields at power frequencies has been investigated by computation and experiment. Different types of low-cost soft magnetic laminations (low-carbon steel, nonoriented Fe-Si, grain-oriented FeSi) and different shield geometries (plane, U-shaped and box-like) have been considered. The shielding factors of model screens have been measured, together with the magnetic flux density in the sheets employed, under field levels typical of industrial environment (~100 μT). Computations have been carried out by means of a hybrid finite-element/boundary element model, which result in good agreement with measurements. It is shown that grain-oriented laminations provide the highest shielding factor, which is reinforced in the plane shield configuration by the addition of an aluminium plate. It is predicted that the screening performance of the U-shaped and box-like shields can be appreciably impaired by the presence of air gaps at the corner joints