In a constant field probe the excitation field on a given material point is invariant under a limited translation of the probe, and the eddy currents are uniform in when the material is free of defects. When superficial defects are present the eddy currents are perturbed. If the probe is provided with a high sensitivity magnetic field sensor with the measurement direction orthogonal to the excitation field, the sensor signal output is correlated to the current perturbation, and indirectly to the defect geometry. The current perturbation may be considered as a collection of current eddies. Thus, the sensor output may be considered as the convolution between the field of a single eddy and the function describing the eddies distribution on the material surface.
In this paper we present a method of inversion based on a kernel method with Tikhonov regularization. The kernel is precisely the field of a single eddy as detected by the magnetic sensor. Using this method it is possible to infer about the surface current density distribution starting from the magnetic sensor signal over a scanned area.