Design of an experiment to measure the acoustic mutual impedances of a resonant, close-packed sonar array

Abstract

Knowledge of the acoustic mutual impedance coefficients for a sonar array is necessary to achieve an accurate analytical description of the performance of the array. In the early stages of a design, analytical approximations, e.g., of an array in an infinite rigid plane baffle, provide adequate estimates. When prototype hardware is available, it may be appropriate to derive refined estimates of the impedance coefficients. This allows more accurate prediction of the effects of design changes on performance, and also provides an analytical baseline for a design that is entering production. The measurement of the mutual impedance coefficients in a resonant, close-packed array is difficult. The only previously reported attempt [Stephen C. Thompson, J. Acoust. Soc. Am. Suppl. 1 68, S34 (1980] achieved inconclusive results, due to inaccurate estimates of the element electromechanical transfer matrices and strong element interactions that occur in the vicinity of the element resonance frequency. These measurements are being repeated, with greater care given to the previously noted deficiencies. The experiment will be described, concluding with the requirements placed on the special transducer elements that were necessary for the measurement. The design of these transducer elements will be described in a companion paper in this session [M. P. Johnson, J. Acoust. Soc. Am. Suppl. 1 82, S2 (1987)].