Improvements in electromagnetic-thermal non-destructive inspection by data processing

Numerical experiment results are processed by various techniques and the improvements in electromagnetic-thermal non-destructive inspection are investigated. The performances of image subtraction, depiction of the norm of the spatial derivatives of temperature and the Fourier transform are evaluated. Compared to the other methods, the cases for which the results are improved by image subtraction are relatively small. The depiction of the norm of the spatial derivatives is more effective, with the 2nd derivative giving better results than the 1st one. The most effective technique is the Fourier transform, which gives satisfactory results even for very distant cracks. The phase images are sharper than the amplitude ones only in cases where the crack is perpendicular to the current flow. Otherwise, the amplitude images are sharper.