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, principal component analysis and independent component analysis, to process the data from the inspection of riveted lap joints by eddy currents. 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 1-10 mm 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 using a receiver operating characteristic approach. In the light of this study, both the techniques appear to be efficient. However, the principal component analysis provides better defect detection results, especially for deeply buried defects.