Harmonic and pulsed eddy current testing methods as tools for surface and subsurface defect evaluation

In most publications eddy current testing (ECT) methods are said to be suitable for surface defects up to several millimeters. This paper aims to evaluate the detection capabilities of eddy current testing based on two examples of modern approach. One of them is a harmonic eddy current method with use of wavelet transformation and neural network. The second method is pulsed eddy current testing (PECT) with use of evaluation script based on cross-correlation of measured data with the set of known reference signals. Two samples with five artificial defects each were investigated from the near and far side. Geometric parameters of every defect were then estimated. Results show that both methods are limited by the skin effect. However, the PECT with use of cross-correlation exhibits detection capabilities of subsurface defects in significant depth. On the other hand, harmonic eddy current testing shows lower errors in dimensions estimation for set of surface defects.