Steel, Geoffrey Alan
(1987).
Techniques for tailoring sonar transducer responses.
University of Birmingham.
Ph.D.
Abstract
This work is concerned with the design of sonar transducers operating in the frequency range 100 kHz to 1 MHz. The transducer frequency responses are predicted using a one-dimensional transmission line analysis. Differences between predicted and measured results are shown to be caused by intermodal coupling between planar and thickness modes of vibration. Conventional transducer designs achieve wide bandwidth using quarter-wave matching layers. In this work the piezoelectric-tunable transducer is investigated as a possible alternative. This structure consists of a pair of ceramics, one of which is driven by a voltage source and the other has a passive electrical load. It is shown that the resonant frequency is variable over more than one octave but the instantaneous bandwidth is only around 10% of the centre frequency. The same transducer can be controlled actively by applying voltages to both ceramics. In this case transducer characteristics are determined by the relative amplitude and phase of the two voltage sources, which can be chosen to give the same results as with passive control. Data is often required for the velocity and attenuation of sound in the materials being used. For this purpose several measuring techniques are described, all of which use a solid buffer rod in place of the more common water tank measurements.
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