A new type of transducer has been developed for use as a shallow-water sound projector at frequencies below 50 kHz. Dubbed the “cymbal,” it is similar to the more commonly known “moonie” and class V ring/shell flextensional designs. Prototype cymbal arrays 2 mm thick with a radiating area of 11.4 cm2 have been developed and calibrated. Two mounting schemes have been examined: unpotted (oil-filled) and potted in a 5-mm thick layer of stiff polyurethane. In both cases, a transmitting response comparable to the more widely used Tonpilz transducer (with an equivalent radiating area) is attainable. When tested under hydrostatic pressures, a standard cymbal configuration has been shown to withstand exposures of 2.5 MPa (which corresponds to 250 m of water depth) before failure.
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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 µm to 250 µm. 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 µm. As a hydrophone, these devices display a sensitivity of −220.7 dB re 1 V µPa−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 µm), this stable and flat sensitivity behavior could be extended to a range from −212 to −225 dB re 1 V µPa−1 and up to 1 MHz. Finite element analysis of this transducer using the ATILA® 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.
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