Approximate Simulation of Low Frequency Magnetic Shielding of a Rectangular Shielding Box Composed of Perforated Walls

The low frequency magnetic shielding of a rectangular metallic box, with all walls perforated periodical holes, is studied. The finite conductivity box with holes and the perfect conductivity box with holes are combined to solve the problem. The first sub model represents the diffusion effect, that is, the magnetic field penetrates the conductive shell, and the second sub model represents the aperture effect, that is, the magnetic field leaks through the hole. The total shielding magnetic field is obtained by superposition of the two submodels. For the diffusion effect, an existing empirical formula is used. For the aperture effect, an approximate simulation technique is proposed: each hole in the walls is modeled as a magnetic dipole. The corresponding dipole moment is obtained according to Bethe’s small aperture coupling theory. Then, the shielded magnetic field inside the box is obtained by superimposing the fields from the dipoles and their images. The full-wave simulations for a rectangular box with a finite conductivity wall are carried out, which shows our approximate technique has good agreement with the full-wave simulations.