Abstract: A calibrator for determining the directivity pattern and complex sensitiv of a line hydrophone array including a calibration chamber, filled with a selected fluid, for sealing the array therein. Projectors, for generating acoustic waves, and monitors, for measuring the amplitude and phase of acoustic waves incident thereon, are mounted within the chamber. The projectors and monitors are connected to a computerized control circuit that drives the projectors to generate a calibration wave, with a predetermined amplitude and phase relative to the center of the array, corresponding to a free plane wave incident at an angle .theta. to the axis of the chamber.

Abstract: A directional hydrophone and electronic circuit combination giving a (cosp.2 .theta.) directivity pattern. A monopole transducer is placed coaxially within a ring transducer and the ring output is fed to a function-conversion electronic circuit which provides a (sin.sup.2 .theta.) output signal. This signal and the output signal of the monopole are fed to a weighted differential amplifier where they are subtracted. The output of the amplifier is a (cos.sup.2 .theta.) signal. By utilizing different components in the function-conversion circuit, the device can be made narrowband or broadband.

Abstract: A small low frequency acoustic receiver which is formed into a cylinder or ing by use of a plurality of separate elements of piezoelectric material. Each element is secured with its sides in face-to-face relationship with an electrode between each joined face in contact with each adjacent element. The electrodes are alternately connected into an electrical circuitry for transmitting electrical signals to a receiver.Other construction techniques may be used to assemble separate elements in a cylindrical arrangement. Over a band of very low frequencies, the cylinder or ring has a high sensitivity (i.e., it produces a large electrical signal) to sound incident in the axial direction compared with its sensitivity in the radial direction. Over this band of very low frequencies the sensitivity of the cylinder or ring is relatively constant for sound incident in the axial direction.

Abstract: A method of ascertaining the piezoelectric constants (d.sub.31, d.sub.33, sub.31, and g.sub.33) of ceramic cylindrical shells (rings) used as the active elements in hydrophones and sound sources to insure quality control. These constants may be obtained by measuring the electrical capacitance of the ring and by measuring the omnidirectional free-field voltage sensitivity, the ratio of the axial and radial sensitivity at a higher frequency and the physical dimensions of the ring. Since the required frequencies are low and the ring is symmetric, the acoustical measurements can be made in a closed mechanically driven air chamber.