Lift-Off Point of Intersection in Spectral Pulsed Eddy Current Signals for Thickness Measurement

Lift-off invariant strategies play an important role in pulsed eddy current (PEC) testing. As an effective signal feature immune to lift-off effect, lift-off point of intersection (LOI) has been applied to determine thickness or evaluate defects. Typically, an LOI feature is extracted from time domain PEC signals. In this article, we observed a novel LOI feature in real and imaginary part of frequency domain PEC responses via simulation and experiment. An analytical model is formulated to investigate the novel LOI feature. It is found that the proposed LOI feature varies with sample thickness increasing, which indicates that the LOI feature from spectral PEC signals could be used for thickness measurement.