Adjusting LOI for Enhancement of Pulsed Eddy Current Thickness Measurement

The liftoff point of intersection (LOI) is a desirable signal feature in the pulsed eddy current (PEC) testing. It is immune to liftoff effect caused by the change of liftoff distance between a probe and a sample. However, adjusting LOI remains an open problem for enhancement of PEC evaluation or extends the application of LOI to thicker samples. In this paper, LOI point could be adjusted by varying the rising time of pulse excitation to extend the measurement range or increase sensitivity for enhancement of the PEC evaluation. The simulations and experiments demonstrate that the difference PEC signal increases and decreases significantly slowly when the rising time of pulse excitation increases. When the rising time of pulse excitation increases, the measurement range of LOI amplitude increases, and the measurement range of LOI time decreases, whereas the sensitivity of LOI amplitude decreases, and the sensitivity of LOI time increases. This investigation helps us to optimize the rising time for the improvement of specific PEC evaluation.