Source separation techniques applied to the detection of subsurface defects in the eddy current NDT of aeronautical lap-joints

This paper investigates the application of two source separation techniques, the principal component analysis and the independent component analysis, to process the data from the eddy current inspection of riveted lap joints. An eddy current array sensor is designed for the rapid inspection of lap-joints and used to test a set of flawed rivet configurations featuring 1 mm to 10 mm long notches, buried down to a 4 mm depth. Implementation methods are proposed for processing such eddy current data by means of both the considered source separation techniques. The signal processing results obtained from the experimental data are compared in terms of source separation efficiency and detection efficiency using a receiver operating characteristic approach. In the light of this study, both the techniques appear to be efficient. However, the principal component analysis better improves the defects detection, especially for deeply buried defects.