The effect of the matching layer thickness on the duration of pulses generated by a transducer

Abstract

Recent publications (e.g., [1, 2]) testify that the problem of investigating the pulsed-mode operation of piezotransducers and choosing the optimal parameters of their components remain topical. Among the problems of applied acoustics, the need for the generation of short acoustic pulses by a transducer is rather common. One of the possible ways of meeting this need is the use of quarter-wave matching layers. The problem of choosing the optimal value of the specific acoustic impedance of the matching layer is considered, in particular, in [3, 4]. In manufacturing high-frequency transducers (with resonance frequencies of about several MHz), special attention should be given to the accuracy of fabricating a layer of the required thickness. This factor is of particular importance when it is necessary to obtain identical characteristics of transducers within a batch where a scatter in this parameter is unavoidable. This paper is devoted to the numerical analysis of the dependence of the pulse form generated by a transducer on the small deviations of the matching layer thickness from the quarter-wavelength. The transducer is considered as a piezoceramic plate (of the TsTBS-3 type) whose rear side is loaded by a damper with the specific acoustic impedance zd and, on the other side, the radiation is emitted into the water medium through a quarter-wave matching layer with the specific acoustic impedance zl. The damper is assumed to be semi-infinite. The electric excitation pulse is taken in the form of a half-cycle of a sine voltage with the period T0 equal to the period of natural oscillations of the piezoceramic plate. The technique for calculating the form of the generated pulse was described in [5, 6]. As before, we estimate the pulse duration by the amplitude decrease to a level of 0.1, i.e., by 20 dB. We introduce a parameter α characterizing in percent the deviation of the matching layer thickness from the quarter-wavelength. The value α = 0 corresponds to the case when the matching layer thickness is equal to the quarter-wavelength. The value α = ±10% characterizes the deviation of the thickness from the quarter-wavelength toward greater or smaller values by one tenth, and so on.