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Defect classification based on wavelet packet energy through pulsed alternating current field measurement technique

In this Letter, a wavelet packet energy-based algorithm is proposed to classify surface and non-surface slits through the pulsed alternating current field measurement technique. Wavelet packet decomposition is used to obtain the coefficient of each frequency band. The slit is classified as non-surface slit or surface slit according to the normalised energy of the first band. The quantification of the remaining ligament or depth of slits is performed using the entropy of the wavelet packet energy. The experiment results show that the non-surface and surface slits can be clearly classified. The entropy of a non-surface slit is linearly proportional to the remaining ligament, and the entropy of a surface slit is inversely proportional to slit depth.