Analytical solution in eddy-current testing of double-layer media with depth-varying magnetic properties

An analytical solution for impedance change in eddy-current testing of double-layer, ferromagnetic media with depth-varying magnetic properties in a half-space is presented. Computational results are given for different values of the parameters of these problems. It is found that if the nondimensional thickness of the top layer is larger than 0.5 the layer can be considered as a half-space. Computations in the case of two-layer ferromagnetic media show that both ends of the curves representing impedance changes due to variations in the thickness of the top layer lie on the corresponding curves for a ferromagnetic half-space.