Short-Time Behaviour in Pulsed Eddy-Current Nondestructive Evaluation
The resurgence of interest in pulsed eddy-current nondestructive evaluation (NDE) is motivated by the ability of the technique to detect deeply-buried defects in multi-layer aircraft structures and to obtain broad-band frequency information [1–4]. In this sense, the pulsed technique is a natural extension of dual- and multi-frequency eddy-current techniques. However, unlike conventional eddy-current NDE, for which the effects of coil lift-off variation can be readily discriminated using phase plane analysis, the most appropriate method for dealing with variation in coil lift-off in pulsed eddy-current NDE remains an open question. Clearly, a first step in the development of algorithms for lift-off compensation is to construct a method to determine the coil lift-off from measurements of the coil response, independent of other variations.