Magnetic Shielding of a Cylindrical Shield in Nonlinear Hysteretic Material

The magnetic shielding efficiency of a cylindrical shield is studied starting from the experimentally determined hysteresis loops of the nonlinear shielding material. The magnetic transfer relation model is used in the frequency domain. This analytical model can be evaluated very fast, but works only for linear material. Therefore, the nonlinear shield is divided into a number of linear sublayers with constant complex permeability, which is modelled by an analytical complex function, fitted from the experimental hysteresis loops. The shielding factors are calculated by the analytical model as a function of the imposed field amplitude. They are validated by a finite element model and compared with measured shielding factors of cylindrical tubes. The correspondence is good for the three considered shields: a shield in aluminium (shielding by induced currents), a shield in Fe-Si steel (mainly shielding by flux shunting) and a multilayered shield in aluminium and Fe-Si steel