A directional dogbone flextensional transducer.

Abstract

Sonar flextensional transducers, in order to transmit energy in one direction, are combined into arrays of elements that are spaced 1/4 wavelength apart. This spacing is dependent on the sound speed of the water; thus, directionality is reduced as the sound speed changes. Here a single projector that is 1/3 wavelength in size that is capable of developing unidirectional beams and independent of sound speed is described. The directional class VII dogbone flextensional is a modified version of an oval shaped class IV flextensional having a concave shell rather than a convex one. The piezoelectric ceramic stack is a trilaminar bar with two active sections separated by an inactive center section. By driving both sections of the stack in-phase, the shell is driven into an omnidirectional radiation pattern. Driving each stack section 180 deg out-of-phase causes a bending mode in the stack, resulting in a dipole radiation pattern. Driving both sections using complex coefficients determined from the omnidirectional and dipole mode patterns, a cardioid directional radiation pattern is developed. Cardioid patterns are developed over an octave frequency band with a front/back pressure ratio of 50 dB. COMSOL/acoustics module FEA code is used to predict in-water electroacoustic performance and compared with experimental data.