Pressure Limitations of Miniature Hollow Sphere Hydrophones

Abstract

Ultrasonic probes that can withstand high pressures and temperatures are needed for deep oil wells, underwater sonar systems, the processing of chemicals, and as automotive actuators. Pressure limits of hollow spherical lead zirconate titanate hydrophones with diameters in the range of 0.5–3.0 mm and wall thicknesses of 50–300 μm have been evaluated using both experimental data and finite element analysis. The spheres were tested at hydrostatic pressures up to 70 MPa (10,000 psi, 7000 meters) and temperatures of 25°C–200°C. The results of the tests and analyses indicate that, at room temperature, unelectroded spheres of all sizes within this size range can withstand pressures up to 7 MPa (1000 psi) and that smaller spheres can survive up to 70 MPa (10,000 psi). Combined temperature-pressure tests on 2 mm spheres indicate survival at temperatures and pressures as high as 200°C and 28 MPa (4,000 psi). Preliminary poling studies indicate that depoling may become a problem at high pressures and elevated temperatures.