Design of actively tuned flexural piezoceramic bar/disk transducers

Abstract

Underwater transducers with variable and controllable resonance frequency can efficiently transmit stepped or linear chirp signals of greater bandwidth by continuously matching their resonance frequency to the dominant frequency of the transmitted signal. This paper presents a technique to vary the first resonance frequency of some widely used underwater transducers: flexural piezoceramic bars and disks. Positive-bias electric fields are added to the driving ac field to generate either a tensile in-plane load in k31 coupling, or a compressive in-plane load in k33 coupling. This load modifies the flexural rigidity of the transducer, which in turn affects its resonance frequencies. Ideally, supported transducers are first analyzed, from the point of view of the electrochemical coupling coefficient at the first resonance, and the frequency shift per applied bias field. Transducers using elastic hinges to approximate simply supported boundary conditions are then examined. The response of the transducers to the combined dynamic bias field and driving ac field is simulated to look for possible dynamic effects, such as the excitation of high-frequency extension and bending modes. Finally, experimental measurements of the coupling coefficient and frequency shift per bias field of prototype transducers are presented. [Work supported by ONR.]