A wideband and high efficiency underwater ultrasonic transducer with a single acoustic matching plate has been presented. The transducer consists of a piezoelectric ceramic resonator, operating in unstiffened longitudinal mode, and a single acoustic matching plate bonded to the ceramic resonator. The matching plate is made of a Al2O3-epoxy composite. The ceramic resonator is T-shaped with a taper, where its polarized part is a thin rectangular bar, which can be driven with low voltage, and where its non-polarized parts comprise a horn part and a head part. The transducer has been designed based on a double mode filter synthesis theory, because it has two resonant modes, whose phases differ byπfrom each other. The optimum specific acoustic impedance and length for the matching plate have been calculated. The 30 kHz array, including four transducers supported at their vibrational nodes, has been fabricated and evaluated. As a result, it has been confirmed that the array has the following characteristics: 33% fractional bandwidth, 211.6 dB sound pressure level re lµPa at l meter,177 dB receiving voltage sensitvity re 1 V/µPa and possible operating depth over 3000 meters. Excellent agreement between theoretical values and experimental results has been obtained. It has been proved that this transducer is useful as a transducer with high resolution for deep oceans.

A finite element method is used to analyze the vibrational characteristics of a quartz crystal tuning fork. From the information obtained by the calculation, the base length of a symmetrical tuning fork can be determined for stability of the fundamental resonant frequency and for very small stresses at the base end. Moreover, the quantitative reason why the effective resonant quality factor Qe of the supported tuning fork with arm corners cut off is highly promoted becomes clear from the analysis in this paper. This desirable characteristic is also realized in the tuning forks either with the circle hole at slit end or with the wide base portion. As for an unsymmetrical tuning fork which is frequently made in manufacturing process, the effects of dimensional unsymmetry on the resonant frequency are analyzed. For compensation of its characteristics caused by unsymmetry, the method of adjusting the length of an arm is usually adapted. It is ascertained whether or not this method is effective for high Qe and high stability of the resonant frequency against change of support condition.