A contribution to the applicability of complex wavelet analysis of ultrasonic signals

Ultrasonic signal is always composed of a series of transient feedback impulsive waves, which are created during the propagation of ultrasonic energy when it meets the discontinuities within the material, such as inclusions, voids, micro-cracks, the surface of the object being inspected and so on. Complex wavelet based envelope detection method was designed to extract the impulsive features contained in the signal. The complex wavelet based correlation analysis was further proposed for distinguishing the 'real impulsive waveform' that indicates the object being searched from a number of unrecognized disturbing waveforms also presented in the signal. The effectiveness of both methods was proved by practical experiments on a common tube sample. The experiments proved that, by using the proposed methods, the impulsive waveform that really indicates the end surface of the tube could be distinguished successfully. With the aid of the analysed results and the calibration equation, the relative distance between the position where the transducer was placed and the end surface of the tube could be identified correctly. It is believed that the proposed methods will be widely applied to the analysis of ultrasonic signals.