Design of a transducer element for an acoustic mutual impedance measurement experiment

Abstract

A companion paper in this session has described an experiment to measure the acoustic mutual impedances in a resonant, close-packed sonar array [S.C . Thompson, J. Acoust. Soc. Am. Suppl. 1 82, S2 (1987)]. This experiment requires the use of special measurement transducers in place of the elements in the array under study. There were several special requirements for these transducers: (1) high mechanical input impedance at the element radiating face; (2) accurate knowledge of the transducer electromechanical impedance matrix; and (3) radiating face dimensions that are identical to those of the elements of the array under study. The first requirement reduces the effects of interelement coupling and, consequently, reduces the sensitivity in the calculations to errors in the measurement. The second acknowledges that the electromechanical impedance matrices of the transducer elements are needed in the calculation. The third requirement provides a measurement array with the same mutual impedance coefficients as the array under study. A prototype transducer element that seems to meet these requirements is a doubly resonant piston element. The element is designed so that the operating band of the array under study falls between the two resonant frequencies of the measurement transducer. The design and performance of this element will be described.