Optimal magnetic shielding of double-layer shields at power frequency

Recently double-layer shields as one type of shields have received attention in magnetic shielding at extremely low frequency. In this paper, the optimal shielding phenomenon is studied by performing theoretical analysis and computations of magnetic fields. Analytic formulas and numerical computation software based on the boundary element method are employed to reveal the inherent relationship between optimal thickness and material properties. It is found that in optimal shielding thickness of one layer is approximately equal to skin-effect depth of another layer. Other conclusions are also derived.