A numerical study of the depth of penetration of eddy currents

The simple standard depth of penetration equation used for most eddy current calculations does not take into account the effects of the size and type of coil, the lift-off or the specimen thickness. The work described in this paper includes a study of the depth of penetration of eddy currents for different coil sizes, including surface- and encircling-type coils, by taking advantage of the sophisticated finite element modelling software COMSOL. Knowledge of these effects plays an important role in designing eddy current coils and the examination of conductive materials with the eddy current technique. This paper includes a study of the effects of all the dimensions of a surface coil, an encircling coil, lift-off and specimen thickness at several excitation frequencies. It is demonstrated by the results obtained from these numerical studies that the coil parameters affect the depth of penetration at different frequencies.