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 fiextensional transmitter with a hinge-lever displacement amplifier has been developed. Investigation reults for the transmitter are reported. The transmitter has a two-stage displacement amplifier. The first-stage amplifier consists of a hinge-lever mechanism. The second-stage amplifier is a tapered oval shell. An electro-mechano-acoustical equivalent circuit is derived for the transmitter. The transmitter was designed, based on the equivalent circuit, and fabricated. For only the shell part, a modal analysis by a finite element method was applied and equivalent circuit constants were calculated. Transmitter dimensions are 36 cm in diameter and 25 cm in depth. The actually obtained resonant frequency is 400 Hz, and the mechanical quality factor is 6.2. A 188 dB source level re 1 µPa at 1 meter was obtained.