Underwater ultrasonic transducers employing ZnO-film/Al-foil composite structure

A ZnO-film-Al-foil composite structure is proposed for developing underwater ultrasonic transducers in the VHF and UHF ranges. Theoretical analysis suggests that it is possible to realize spurious-response-free, wide-bandwidth, high-efficiency transducers by properly determining the thicknesses of the Al foil and the ZnO film. A ZnO-film-Al-foil underwater ultrasonic transducer was fabricated by DC magnetron sputtering. Being air-backed, the transducer generates 102-MHz ultrasonics into water over a -3-dB bandwidth of 8.2 MHz without any appreciable spurious response. The minimum conversion loss of the transducer is about 11.6 dB, which is due mainly to the effect of electric resistivity and mismatching. By transforming the shape of the Al foil to the ZnO film deposition, a concave transducer was also fabricated. It is confirmed that the ultrasonics launched from the concave transducer are focused on some particular point.<>