A system and method for nondestructive testing of a workpiece having a metallic protective coating utilizing nonlinear harmonics techniques to determine degradation within the metallic protective coating. The invention use a time-varying magnetic field to sense magnetic properties of the protective coating. The odd-numbered harmonic frequencies are detected and their amplitudes are related to the magnetic condition of the material under test to determine coating degradation. When no harmonic signal caused by an induced magnetic field is detected, the coating is not degraded. When a harmonic signal is detected, the coating has degraded. Nonlinear harmonics techniques are used to determine the amount of coating degradation.
Gary L. Burkhardt; Hegeon Kwun