Miniature piezoelectric hollow sphere transducers (BBs)

Miniature piezoelectric transducers were prepared from millimeter size hollow spheres which were formed from PZT-5A powder slurries using a coaxial nozzle process. After sintering, the spheres were poled in two ways: radially and tangentially. Principal modes of vibration were found to be a breathing mode near 700 kHz and a thickness mode near 13 MHz for the radially poled spheres, and an ellipsoidal, a circumferential, and a breathing mode near 230, 350, and 700 kHz, respectively, for tangentially poled spheres. Coupled modes were also observed at higher frequencies. These same modes with similar frequencies were obtained from finite element analysis using the ATILA FEM code, and experimental results were shown to be consistent with the modeling study. Hydrostatic d/sub h/ coefficients ranged between 700 and 1,800 pC/N, which is considerably higher than the d/sub h/ of bulk PZT. The hydrophone figure of merits (d/sub h/*g/sub h/) were calculated to be between 68,000 and 325,000*10/sup -15/ m/sup 2//N for various types of poled spheres. These values are three orders of magnitude higher than the bulk PZT figure of merit. Potential applications include ultrasonic imaging, nondestructive testing, and hydrophones.