Simultaneous Detection of Defect and Lift-off Using a Modified Pulsed Eddy Current Probe

In this paper, a new and efficient lift-off detection technique suitable for pulsed eddy current (PEC) based non-destructive testing probe is presented. In the proposed method lift-off is determined by measuring the leakage current through the distributed capacitance that is present between the probe and the target. The distributed capacitance changes as a function of lift-off. The front-end electronics of the PEC probe is modified such that the defect detection, using PEC, and lift-off sensing, using the change in the distributed capacitance, operates simultaneously. The new scheme requires no change in the sensing element of the PEC probe. The new technique was modeled, simulated, tested and experimentally validated using a prototype developed. The lift-off detection technique was found to be insensitive to the typical defects of the target and sensitive only to the lift-off. This technique is novel as the lift-off is sensed using the change in the distributed capacitance itself and both the lift-off and defect detection occurs simultaneously. The new scheme requires minimal additional hardware and no change to the probe. The proposed approach helps to achieve reliable defect detection using the PEC probe.