A Directional Dogbone Flextensional Sonar Transducer
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.