Nondestructive evaluation of the severity of discontinuities in flat conductive materials by an eddy-current transducer with orthogonal coils

This work presents two methods for nondestructive evaluation of the severity of material discontinuities in nonmagnetic conductive plates by eddy currents generated by a transducer with orthogonal coils. The first method deals with long rectilinear discontinuities located beneath the surface under test and having a negligible width. It is based on the geometrical theory of diffraction of electromagnetic waves generated by the transducer. The conditions under which a real transducer satisfies the diffraction model hypotheses are specified. In this case, the experimental results are in good agreement with the theoretical ones. The second method concerns small volumetric discontinuities whose shape and size are evaluated by an eddy-current holographic procedure. When the discontinuity size is comparable with that of the transducer, this permits reconstruction of the shape and determination of the depth of the discontinuity beneath the surface under test.