Null-image effect of planar coils over a grounded ferrite slab

This paper presents a rigorous formulation based on the inverse Fourier–Bessel transform to determine the contribution of non-conservative electric fields (or vector potentials) due to a circular current filament from the actual and image currents, respectively. Notably, the null-image effect in the scenario of a current loop filament positioned at a distance h from the magnetic substrate surface can be observed. Specifically, the position where the measured electric field due to image current vanishes is a function of both and ferrite slab thickness, where d is the distance from the excited coil to the pick-up coil.