The performance of an acoustic transducer is determined by the effects of many structural variables, and in most cases the influences of these variables are not linearly independent of each other. To achieve optimal performance of an acoustic transducer, we must consider the cross-coupled effects of its structural variables. In this study, with the finite-element method, the variation of the operation frequency and sound pressure of a flextensional transducer in relation to its structural variables is analyzed. Through statistical multiple regression analysis of the results, functional forms of the operation frequency and sound pressure of the transducer in terms of the structural variables were derived, with which the optimal structure of the transducer was determined by means of a constrained optimization technique, the sequential quadratic programming method of Phenichny and Danilin. The proposed method can reflect all the cross-coupled effects of multiple structural variables, and can be extended to the design of general acoustic transducers.

A class IV flextensional transducer is a typical underwater acoustic transducer capable of generating high power sound waves. The small extensional displacement of a piezoceramic stack in the major axis of the transducer causes a large displacement along the minor axis by the leverage effect of a compliant shell, and this provides the large volume displacement for high power acoustic waves. High power and long term usage of the transducer causes accumulation of a lot of heat inside the structure, which results in the transducer performance to deteriorate. In this study, the effects of the structural variables of the transducer were investigated using the finite element method, and their influences were prioritized to design a transducer to have the highest sound pressure with the lowest heat generation at a desired operation frequency. The transducer designed showed an 11.2% increase in its sound pressure and a 16.5% decrease in its heat generation in comparison with a basic model of a conventional structure.

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In an ultrasonic transducer, the cross talk between array elements is an important performance degrading factor, and there is strong need to identify the sources of the problem and to find the means to reduce its level. This paper considers two most representative ultrasonic transducers, capacitive micromachined ultrasonic transducer (cMUT) and piezoelectric transducer. Both are linear array immersion transducers. Two-dimensional finite element models of the transducers are constructed using the commercial code ANSYS. We analyze the origin and level of the cross talk between array elements, with evidence of coupling through certain waves such as the Stoneley wave propagating at the transducer-water interface and the Lamb wave propagating in the substrate or the impedance matching layer. For reduction of the cross talk level, the effects of various structural schemes are investigated. They are the change of wafer thickness, the installation of etched trenches of various dimension and sound absorbing materials inside, and installation of polymer walls between array elements for a cMUT as well as the change of the dimension and material of kerfs for a piezoelectric transducer. Results for the two transducers are discussed to describe the general method to reduce the cross talk level in ultrasonic transducers.