Abstract: A sonar array which is operable at a broad range of frequencies, has a high free-field voltage sensitivity and is operable at high hydrostatic pressures. The array includes sensor elements made of a piezoelectric material, a backing plate which supports the sensor elements, a dielectric-elastic insulator positioned between the sensor elements and the backing plate, and backing blocks corresponding, respectively, to the sensor elements, each backing block positioned between a corresponding sensor element and the insulator. The sensor elements are arranged in staves, the staves forming four separate quadrants, the sensor elements in each stave being arranged in parallel and series combinations, so that the sonar array is operable between a frequency range of 10 kHz to above 100 kHz, each stave has a free-field voltage sensitivity of -186 dB re 1V/.mu.

Abstract: A hydrophone preamplifier design utilizing hybrid integrated circuits, surface mounted components, multi-layered circuit boards and gain switching. Acoustic signals from a sensor are applied to a hybrid integrated circuit preamplifier whose gain is controlled by a relay activated remotely from a control that allows a predetermined attenuation permitting measurements of high sound pressure levels (low gain) or low ambient noise levels (high gain). The preamplifier in the hybrid integrated circuit provides a gain of 10 (20 dB) and an additional gain of 10 is provided by a low-noise operational amplifier (op amp). A current booster provides the output current drive capability for the preamplifier which is capable of driving large capacitive loads and has protection against both electrical and thermal overloads. Insertion calibration is provided through an ac current signal supplied by an external source, which develops a small voltage signal when supplied to the preamplifier.

Abstract: A hydrophone preamplifier control unit provides for front panel controls and cable connectors for applying a calibration current and operating voltage to the hydrophone, controlling the level of these voltages, and monitoring the operation of the hydrophone. The control unit assures the continuity of the electrical circuits to a hydrophone through the use of a calibration current applied to the hydrophone through the use of a calibration current applied to the hydrophone through an interconnecting cable.

Abstract: The frequency modulated monitor hydrophone system which is used to monitor low frequency sound signals where cross-talk coupling is a problem, consisting of a hydrophone, preamplifier and receiver which includes a control group. The hydrophone comprises an acoustic sensor and low-noise preamplifier utilizing dynamic range compression to condition the electrical acoustic sensor signal before it is frequency modulated (FM) and applied to a coaxial cable. At the remotely located receiver, the FM signal from the hydrophone preamplifier is filtered to remove undesirable signals, such as audio spectrum crosstalk and out of band signals. The partially recovered audio signal is decompressed utilizing dynamic range decompression, amplified, and output for utilization or recordation by an operator. A calibration circuit provides a continuity or partial calibration check for the hydrophone by applying a signal of predetermined frequency and voltage to the hydrophone preamplifier and sensor.