SOME ANALYSES OF TRANSIENT CHARACTERISTICS OF THICKNESS MODE PIEZOELECTRIC TRANSDUCERS BY USING MASON’S EQUIVALENT CIRCUIT

We computed, by using Mason's equivalent circuit, the acoustic waveforms radiated by thickness-mode piezoelectric circular transducers, possessing various structure parameters and being excited by a step voltage. We also computed the electrical waveforms produced by these transducers when they were used for receiving as well as for tansmitting, the radiated acoustic pulses being reflected by a plane boundary. Measurements were made with a thin measuring transducer at a close range in the first case or with the reflector also very close tothe transducer in the second case. On comparing the theoretical and the experimental results, it may be seen that in spite of the fact that Mason's equivalent circuit is a one-dimensional model, computed results are reasonably applicable. Some theoretically predicted details, such as the asymmetry of the radiated acoustic waveforms about the time axis, are experimentally confirmed. But then there remain some yet to be elucidated problems such as to what extent does the assumption hold that the radiated ultrasonic wave is plane.
The influence of the wear plate is briefly discussed. Illustrations are given showing that distortion in the waveform and change in the apparent ultrasonic frequency become more prominent when the thickness increases. Mention is made of the possibility of controlling the electrical waveform obtained from a transmitting-receiving transducer such that the maximum of its envelope is to occur either at the very beginning or at some cycles later.