Underwater multimode directional transducer evaluation

Abstract

An underwater piezoelectric directional transducer prototype, to be used in underwater acoustic networks, combines different vibration modes of a cylinder to synthesize desired beam patterns. Performance is evaluated in an anechoic water tank, with reference hydrophones and a signal analyzer capable of Fast Fourier Transform (FFT) data processing. An impulse technique is used for measuring impedance, admittance, Transmitted Voltage Response (TVR), Receiving Voltage Sensitivity (RVS), and horizontal and vertical beam patterns. In this technique, a single-cycle tone burst is emitted at a low frequency repetition rate and excites the driving transducer. The signal analyzer excludes the acoustic reverberations from the tank walls by adequate adjusting of the FFT sampling window. Additionally, for beam-pattern data acquisition, a computer simultaneously samples the azimuthal orientation of the prototype relative to a reference hydrophone and the corresponding frequency response, as the evaluated transducer continuously rotates. The FFT capability of the signal analyzer also supports intrinsic noise evaluation. The results show that the new transducer architecture is capable of producing directional beam patterns according to the present operational requirements by electronic control of the internal electrode applied voltage distribution.