Defect-depth dependence of optimal frequency and spatial resolution in SQUID based NDE

We have investigated the relationship between the excitation frequency and the depth of the flaws in our SQUID based NDE system to achieve optimum frequency for the detection of each particular flaw depth in the metallic samples. Also, the system resolution defined as the gap's distance between the two edges of a crack in the samples, have been experimentally investigated and the dependency to the frequency and the input excitation voltage amplitude was found. Afterwards, we have simulated the system in COMSOL Multiphysics using a basic model for the coils, and examined some special flaws to obtain their effects on the magnetic flux density caused by the eddy current distribution.