A new ultrasonic composite transducer implemented with thick filmtechnology

摘要

A new ultrasonic transducer operating in air and fabricated bynthick film technology is presented. It consists of a compositenmechanical structure in which three active elements, made with planarnalumina substrates supporting PZT-based piezoelectric films, behave asnelastic guides. The active elements have a constant rectangularncross-section and are radially placed, 120° apart. They are mountednbetween a rigid base (operating as the acoustic backing) and an aluminandisk. On both sides of each substrate a piezoelectric layer hasninterdigital thick-film electrodes embedded in layer itself, so that itncan be polarized parallel to the long side of the active element;nconsequently, it allows the creation of periodic surface stressesnresponsible for symmetric extensional strains in the alumina plates. Thenelements, synchronously driven in phase, form, with the disk, anvibrating resonant structure, which radiates acoustic energynperpendicular to the disk surface. The assembly of active elements,nacoustic backing and radiating disk forms a composite ultrasonicntransducer operating in air without the need of any acoustic matchingnlayer. Among the prominent features offered by the transducer designnare: a transduction efficiency of 25% at an exiting voltage of 100nVp and a high directivity of the emitted beam