Three-dimensional defect localization from time-of-flight/eddy current testing data

This paper deals with the inverse problem of defect detection in a conductive material using eddy current nondestructive evaluation (NDE) methods. We consider a full three-dimensional time-domain problem in the quasistatic regime. The inversion method exploits the properties of the Q-transform, an integral operator capable of mapping wave propagation fields into diffusive fields. This one-to-one operator allows one to define the concept of time-of-flight (TOF) for diffusive fields. Specifically, we show that by properly choosing the waveform of the driving current, the distance between probe and defect can be easily extracted from eddy current measurements, as in TOF measurements employed in wave propagation NDE methods.