Analytical Model for Low-Frequency Magnetic Field Penetration Through a Circular Aperture on a Perfect Electric Conductor Plate

We propose an approximate analytical model for magnetic field penetration through a circular aperture on a perfectly conducting plate. The magnetic field source is a circular loop current placed parallel to the plate and coaxial with the aperture. It is shown that the aperture is equivalent to a magnetic quadrupole normal to the plate when the field point is far from the aperture. The model is validated using numerical simulations and a minor disagreement with experimental data is explained.