Localization of Reflectors in Plates by Ultrasonic Testing with Lamb Waves

An algorithm is suggested for localizing flaws in thin-walled objects based on the analysis of dispersion characteristics of Lamb waves. It is shown that applying the technique of determining the instantaneous signal frequency by means of wavelet transform makes it possible to reconstruct extensive sections of frequency dependences of the group delay time for different modes of Lamb waves. An extra merit of the proposed method is its high noise immunity. It has been established that an optimum choice of the frequency range is required to minimize the experimental error, namely, in order to minimize the inaccuracy in determining distance one should choose the dispersion-characteristic section where the group delay time is long as compared with its nominal value while its frequency variation is maximum.