A new acoustic transducer with a pressure-deformed piezoelectric diaphragm

A new design for wide-band acoustic transducers is described. Radial tension is applied to a thin piezoelectric diaphragm with conductive electrodes on the upper and lower surface. One side of the diaphragm is pressurized, elastically deforming the diaphragm into a slightly curved shape. The in-plane static tension is modulated by applying a time-dependent voltage across the electrodes of the piezoelectric diaphragm. The tension modulation causes transverse displacement oscillations of the diaphragm. This actuation takes place in spite of the fact that the piezoelectric diaphragm does not contain a passive elastic layer, which is necessary for actuation by flexure in planar diaphragms. A theoretical quasi-static model using hexagonal symmetry for the piezoelectric material was developed to predict the electromechanical actuation mechanism, and the mode for optimal operation in non-resonant conditions. Piezoelectric diaphragms were fabricated from PVDF film of nominal thickness 40 μm into circular diaphragms 1 cm in diameter. For the pressure-deformed transducers fabricated from PVDF film, displacement amplitudes of 9–14.5 nm/V were observed, and the maximum displacement amplitude took place at the applied tension and static pressure predicted by the model. Additional measurements with conventional flexure-type transducers containing a diaphragm consisting of a layer of PZT and a passive elastic material fabricated using MEMS processes were performed to compare with the transducers fabricated from PVDF film. The displacement amplitude per unit electric field measured for the transducers fabricated from PVDF film was comparable to those measured from conventional PZT flexure-type transducers, despite the fact that the piezoelectric coupling coefficient for PVDF was approximately 100 times smaller than that for PZT.