Time-of-flight measurement of ultrasonic pulse echoes using wavelet networks

This paper deals with the digital processing method based on wavelet network (WN) to measure the time-of-flight (ToF) between the ultrasonic pulse and echo reflected by the target. The measure is carried out once the WN is trained to model the cross correlation between the signals coming from the ultrasonic transducer and the reference one. The aspects concerning the modeling by the WN of the cross correlation and, in general, of the nonlinear function are taken into account. An innovative procedure to initialize and to train the WN is pointed out to ensure high accuracy and good generalization. After a brief outline of the theory underlying the WNs, all the fundamental steps of the measurement method are described in detail. The results of the experimental tests carried out for method validation and characterization are shown. Finally, comparative tests between the virtual instrument based on the proposed measurement method and the ultrasonic digital indicating tester are given and discussed.