Design, performance and modeling of piezoceramic hollow-sphere microprobe hydrophones

This paper describes the design and performance of a small, high-frequency, piezoelectric, underwater probe. The probes are fabricated from miniature, thin-wall, lead zirconate titanate ceramic hollow spheres with radii (r) from 0.5 mm to 2.5 mm and wall thickness (t) from 50 mu m to 250 mu m. The experimental results reported in this paper are focused on devices prepared from hollow spheres with an outer radius of 1.38 mm and a mean wall thickness of 75 mu m. As a hydrophone, these devices display a sensitivity of -220.7 dB re 1 V mu Pa-1 at 250 kHz that stays flat to within +/-3 dB over the frequency range from 10 kHz to 450 kHz with an omnidirectional response. Within the accessible range of sphere sizes (r = 0.5-2.5 mm, t = 50-250 mu m), this stable and flat sensitivity behavior could be extended to a range from -212 to -225 dB re 1 V mu Pa-1 and up to 1 MHz. Finite element analysis of this transducer using the ATILA (R) software is also included in this paper, comparing the computational results with the results from the experimental measurements. Based on the excellent agreement obtained, a parametric modeling study was also undertaken and its results are discussed in this paper. The miniature ceramic hollow-sphere transducers fill a gap in the frequency range of 200 kHz to 1 MHz with an omnidirectional response and much higher sensitivity than other ceramic and polymer piezoelectric probes.