Numerical Modeling and Material Characterization for Multilayer Magnetically Shielded Room Design

In this paper, a method for the assessment of magnetic properties of ferromagnetic materials at low magnetic field values is presented. The knowledge of these properties is crucial for the design of magnetically shielded rooms that must be effective against low-frequency external magnetic field disturbances on the order of 0.1-1 μT. The considered shielding structure is composed by a number of layers made of different high-permeability ferromagnetic sheets as grain-oriented electric steel and nickel-iron soft magnetic alloy. The ferromagnetic materials in this region follow the Rayleigh law that is a quadratic law between magnetic flux density and the applied field. Two material-dependent parameters of this law are obtained by a characterization of the material behaviour performed on a scaled prototype of a magnetically shielded room. The procedure is validated on a multilayer shield structure.