A compact Terfenol-D vector projector

Abstract

In active sonar applications, it is desirable to have a directional, steerable sound source to accelerate the target localization process. A narrow cardioid beam pattern with approximately 78° beam width and rear side lobes 25 dB down can be generated by combining monopole, dipole, and quadrupole beam patterns with appropriate amplitudes and phases. A cylindrical array composed of eight Terfenol-D Tonpilz transducers arranged in two rings with each transducer pointing radially outward from a common center mass has been developed to generate narrow cardioid beam patterns. Focus during the design process was on minimizing size, maximizing the bandwidth, and maximizing the duty cycle. The diameter of the source is 0.19 wavelengths at the lowest operating frequency and 0.76 wavelengths at the highest operating frequency. Bandwidth of the source is greater than two octaves. Lumped parameter modeling and finite element modeling are used to demonstrate the monopole, dipole, quadrupole, and narrow cardioid beam patterns. The effects of extraneous vibration modes on the beam patterns and sound output are discussed. Maximum continuous wave sound output and duty cycle at maximum output are estimated from thermal models and test data from a single Tonpilz element. [Work supported by the Office of Naval Research.]