A hydrophone is an underwater microphone or transducer used to detect underwater sound. The sensitivity of a hydrophone is determined by the voltage that is produced by a hydrostatic pressure wave. The hydrostatic voltage coefficient, gh, relates the electric field appearing across a transducer to the applied hydrostatic stress, and is therefore a useful parameter for evaluating piezoelectric materials for use in hydrophones. Another piezoelectric coefficient frequently used is the hydrostatic strain coefficient, dh, which describes the polarization resulting from a change in hydrostatic stress. The gh coefficient is related to the dh coefficient by the relative permittivity (K): gh = dh/ɛoK, where ɛo is the permittivity of free space.

Composite piezoelectric sensors

Polymer-ceramic composites with different connectivity designs have been developed. The piezoelectric d and g coefficients of these composites in hydrostatic mode were characterized as a function of pressure, temperature, and frequency. All composite samples exhibited piezoelectric properties greatly improved over those of conventional piezoelectric ceramics. However, the introduction of soft polymer matrix caused the composite properties to be highly pressure-dependent. The effect of reinforced polymer matrix on the temperature and pressure dependences of the piezoelectric coefficients was also investigated. Prototype hydrophones containing the composite samples were designed and evaluated for their free-field voltage sensitivity. The potential use of polymer-ceramic composites for underwater acoustic applications is discussed.

Evaluation of new piezoelectric composite materials for hydrophone applications

A glass with the composition 2BaO·TiO2·2.75SiO2 was annealed at 810 °C for 20 h. This led to surface crystallization. Immediately at the surface of the sample, a layer of Ba2TiSi2O8-type fresnoite ...

Electron Backscatter Diffraction of Fresnoite Crystals Grown from the Surface of a 2BaO·TiO2·2.75SiO2 Glass

The Crystal Structure of Sr2TiSi2O8

Fresnoite glass-ceramics – A review

Glass ceramics are shown in this study to be a new class of transduction materials for application in sonar transducers. It is found that glass ceramics of Ba2TiSi2O8 have high hydrostatic voltage sensitivity, low dielectric loss, and low dielectric constant. These properties are also shown to be practically independent of pressure up to 35 MPa. The free‐field voltage sensitivity of a glass‐ceramic prototype hydrophone is higher than that based on a commonly used lead zirconate titanate ceramic element.

Polar glass ceramics for sonar transducers

Hydrostatic piezoelectric strain coefficients dh (~10 pC/N) and voltage coefficients gh (80–100×10-3 V m/N) on single crystals of Ba2TiSi2O8, Ba2TiGe2O8 have been measured as a function of temperature, pressure, and frequency. The values are found to be comparable to those of the state of the art piezoelectric PVDF polymers. Measurements are also made on the glass-ceramics in the compositions of BaO–TiO2–SiO2 and some isostructural materials compositions in the system BaO–TiO2–GeO2. The typical values of the piezoelectric constants of glass ceramics are almost on the order of those obtained on the respective single crystal samples. Glass-ceramics provide a promising way of achieving the larger area samples needed for various piezoelectric devices.

R. Y. Ting

Papers

Polar glass ceramics for sonar transducers

New Materials for Hydrophone Applications- Single Crystals and Polar Glass-Ceramics