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 severit y of material discontinuities in nonmagnetic conductive plates by eddy curr ents generated by a transducer with orthogonal coils. The first method deal s with long rectilinear discontinuities located beneath the surface under t est and having a negligible width. It is based on the geometrical theory of diffraction of electromagnetic waves generated by the transducer. The cond itions under which a real transducer satisfies the diffraction model hypoth eses are specified. In this case, the experimental results are in good agre ement with the theoretical ones. The second method concerns small volumetri c discontinuities whose shape and size are evaluated by an eddy-current hol ographic procedure. When the discontinuity size is comparable with that of the transducer, this method permits reconstruction of the shape and determi nation of the depth of the discontinuity beneath the surface under test.