Investigation on Time-to-Peak Feature Insensitive to Liftoff Effect for Pulsed Eddy Current Evaluation

The influence of liftoff variation on the peak value and time-to-peak feature of pulsed eddy current (PEC) signals is investigated in this article by simulations and experiments. First, PEC response is analytically modeled via Fourier transform for simulations. In an alternative way, PEC response is formulated with Laplace transform. Using an approximation of Laplace transform-based PEC formulation, the physics that liftoff distance only changes the amplitude of PEC responses rather than shifting the position of peak heights is discovered. Second, simulations were implemented, and the results demonstrate that the time-to-peak feature is insensitive to liftoff variation, i.e., around one-fourth of the peak value. Finally, the experimental results agree well with those from the simulations, which validates the physics that the time-to-peak feature is insensitive to the liftoff effect.