A new ultrasonic composite transducer implemented with thick film technology

A new ultrasonic transducer operating in air and fabricated by thick film technology is presented. It consists of a composite mechanical structure in which three active elements, made with planar alumina substrates supporting PZT-based piezoelectric films, behave as elastic guides. The active elements have a constant rectangular cross-section and are radially placed, 120/spl deg/ apart. They are mounted between a rigid base (operating as the acoustic backing) and an alumina disk. On both sides of each substrate a piezoelectric layer has interdigital thick-film electrodes embedded in layer itself, so that it can be polarized parallel to the long side of the active element; consequently, it allows the creation of periodic surface stresses responsible for symmetric extensional strains in the alumina plates. The elements, synchronously driven in phase, form, with the disk, a vibrating resonant structure, which radiates acoustic energy perpendicular to the disk surface. The assembly of active elements, acoustic backing and radiating disk forms a composite ultrasonic transducer operating in air without the need of any acoustic matching layer. Among the prominent features offered by the transducer design are: a transduction efficiency of 25% at an exiting voltage of 100 V/sub p/ and a high directivity of the emitted beam.