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A Directional Dogbone Flextensional Sonar Transducer

S.C. Butler
Naval Undersea Warfare Center, Newport, RI, USA

In order to transmit energy in one direction, sonar flextensional transducers are combined into arrays of elements that are spaced a 1/4 wavelength apart. The directionality (front-to-back pressure ratio) is a modest of 6 dB. A single projector that is 1/3 wavelength in size and capable of developing unidirectional beams with front-to-back ratios greater than 20 dB that is independent of sound speed is described here. The piezoelectric ceramic stack is a tri-laminar 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 omnidirectional radiation pattern. Driving each stack section 180 degrees out-phase causes a bending mode in the stack resulting in a dipole radiation pattern. By driving both sections using complex coefficients determined from the omnidirectional and dipole mode patterns, a cardioid directional radiation pattern is developed. COMSOL Multiphysics and the Acoustics Module are used to predict in-water electroacoustic performance and compared with an experimental data.