Displacement amplification in curved piezoelectric diaphragm transducers

Experimental measurements of the displacement amplitude of a special curved piezoelectric diaphragm-type transducer are presented. The diaphragm consisted of a laminated PZT structure, square in shape, 4 mm side length, and 4.1 μm total thickness. The transducer was formed by applying a static pressure to one side of the diaphragm that deformed it into a nominally spherical shape. This transducer was similar to curved transducers previously described in the technical literature except that the diaphragm vibrated under tension and static pressure. Scanning laser vibrometer and cursory acoustic measurements were performed to characterize the performance of the transducer. The amplitude of diaphragm vibrations per supplied volt varied by 39 dB and the first natural frequency gradually changed as the static pressure was increased. The displacements at the first natural frequency were observed to be in-phase across the diaphragm surface, as contrasted to the phase variation observed in the first flexural mode of the curved transducers described in the literature. The implication is that a curved transducer formed by the application of external static pressure offers high-displacement amplitude and a low-frequency mode that would couple efficiently to a surrounding acoustic medium.