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Reference wavelets used for deconvolution of ultrasonic time-of-flight diffraction (ToFD) signals

One major disadvantage of ultrasonic time-of-flight diffraction (ToFD) technique is the weakness of echoes which are diffracted from crack tips. This shortcoming, to some extent, can be overcome by application of proper signal processing techniques. Deconvolution techniques have shown to be quite effective for this purpose. A deconvolution process needs to use a reference wavelet in order to extract the required information from the signal. Accordingly, one of the major challenges in using deconvolution techniques is the choice of the reference wavelet. This paper discusses some of the problems encountered in the selection of the reference wavelet and proposes methods to overcome these problems. The angle-dependent deconvolution technique is one of these methods in which the reference wavelet used for processing each part of the signal is different from wavelets used for other parts. The principles of this method are described and its effectiveness is demonstrated by both simulation and experiment.