Optimally formulated high efficient planar projector arrays

Abstract

Closely packed multi-element transducer arrays are extensively used in underwater applications for achieving better directionality and longer transmission range. With the current tendency of extending their operation toward lower frequency and particularly near resonance, the acoustic interaction among the elements grows stronger and in turn will degrade the predicted transmitting characteristics. This troublesome effect is much alleviated in uniform planar arrays by restructuring it with the optimal interelement spacing at which the interaction force is minimum [P.M. Joseph and P. R. Saseendran Pillai, Acoust. Lett. 12 (11), 190—193 (1989)]. It has been seen from the results of computation that a further reduction in interaction can be achieved by incorporating the nonuniform array concept. A simple method for predicting the optimum configuration of element locations that reduce the interaction to a lower level, without altering the aperture dimension, is proposed in this paper. Here, the element locations are dispersed in accordance with Gaussian distributed random numbers by keeping the optimum spacing as the mean. Even though a large standard deviation value will greatly reduce interaction, a reasonable value is chosen, as large deviations produce deteriorated beams. This optimally formulated array does not exhibit any grating lobes nor does its radiation pattern differ much from the conventional λ/2 spaced and restructured arrays.