Abstract: An accelerometer for measuring the vertical component of acceleration independent of the accelerometer orientation or the pressure. The accelerometer is particularly adapted for use in marine surveys in combination with a hydrophone to cancel the surface reflected wave.

Abstract: A piezoelectric ceramic cylinder is positioned between a vibratile piston and a matched rigid mass element. To prevent corona, the electrodes on the ceramic cylinder are covered with an insulating material in the region near the edges of the electrodes where a corona might otherwise form. A low-loss rubber compound and a molded rubber support cradles the transducer assembly. A special manufacturing technique uses a standard weight supported on the cylinder to affect the resonant frequency of the cylinder and enable them to be segregated into classes according to their resonant characteristics.

Abstract: An electroacoustic transducer having high acoustic-to-electric energy conversion per unit volume. The transducer is in the form of a body having a cylindrical central section and hemispherical end sections, the central section and the end sections formed from active piezoelectric material and electrically interconnected with respect to a pair of output terminals wherein the polarizations of the central section and the end sections are arranged to convert acoustic pressure on the entire external surface area of said body to be effective in producing electrical energy. The physical parameters of each section are matched to produce essentially equal electrical characteristics of each section to form an inherently symmetrical transducer. The transducer has high sensitivity for a small size and is especially adapted for use in thin line towed arrays. The symmetrical form, polarities and balanced connections of the transducer provide cancellation of forces due to acceleration.

Abstract: The utility of a coaxial electret cable transducer as a hydrophone at shallow depths (low hydrostatic pressure) is extended for operation at substantially greater depths (high hydrostatic pressure) by the combination of the electret with a polymer material having piezoelectric properties, i.e., a piezoid. The electret and piezoid are separate flexible materials radially stacked within the cable or alternatively and preferably constitute a single material formed to have both electret and piezoelectric properties. One substance useful as the piezoid or as the electret-piezoid combination is polyvinylidene fluoride (PVF.sub.2).The invention also comprehends the method of measuring underwater soundings at either low or high hydrostatic pressures with the aforementioned coaxial cable as an electrostatic transducer by measuring electrical signals generated across the cable conductors when the ambient pressure is low and as a piezoelectric transducer across the conductors when such pressure is high.

Abstract: A pressure-balanced hydrophone having a low cut-off frequency which inclu a pair of piezo-ceramic tubes, wired in series, and having one end of each tube secured to a metal block in the center. The second end of one of the ceramic tubes is covered by means of a solid metal end cap and the second end of the other ceramic tube is covered by a porous sintered metal end cap. The unit is enclosed in an elastomeric cylindrical boot which is closed at the open end by a metallic disc. A pair of fill plugs are provided to fill the interior and the exterior of the piezo-ceramic tubes with a suitable oil. The unique feature of subject device is that a plurality of pores in the porous sintered metal end cap act as a plurality of capillaries for pressure balancing and thus make the hydrophone insensitive to hydrostatic pressure variations.