Piezoelectric hollow spheres for microprobe hydrophones

Abstract

Miniature hollow spheres of lead zirconate titanate have been prepared with a coaxial nozzle process using fine grain slurry of PZT-5. Following the binder burnout and sintering, the spheres were poled radially and tangentially to be tested as piezoelectric transducers for underwater microprobe hydrophone applications. For the radially poled spheres the principal modes of vibration were found to be breathing and thickness modes with breathing mode resonance shifting to lower frequencies with increasing sphere size. For tangentially poled spheres, the main modes were determined to be an ellipsoidal, a higher order circumferential, and breathing modes near 230 kHz, 350 kHz and 700 kHz, respectively. Higher frequency coupled modes were also observed. Hydrostatic piezoelectric charge coefficients (dh) of the transducers were measured to obtain a hydrophone figure of merit for microprobe applications, resulting in d(li) values ranging from 600 to 1,800 pC/N. These values are substantially higher than that of bulk PZT transducers.