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.

Wide-band, low-ripple underwater transducers with high-power acoustic radiation capability have been designed on the basis of multiple-mode filter synthesis theory. They are composed of triple acoustic matching plates and double backing plates with optimized specific acoustic impedances,besides piezoelectric ceramic elements. One of the backing plates employs a Fe damping-alloy to suppress unwanted response peaks in the frequency range above the passband region. Two 33 array transducers were fabricated, each with a center frequency of 200 kHz, one as a transmitter and the other as a receiver. The two transducers show high-sensitivity, low-ripple and wide-band transmitting and receiving responses. Then, the transducers were applied in a color video picture digital transmission system.Clear color video pictures, composed of 256240 pixels, were successfully received within one second.