(redirected from Hydrophones)
Also found in: Dictionary.


(hī`drəfōn'), device that receives underwater sound waves and converts them to electrical energy; the voltage generated can then be read on a meter or played through a loudspeaker. The hydrophone is the marine equivalent of the microphone, which receives and converts sound waves in air. It is used in sonar apparatus and in certain underwater weapons. The same device may also be used to generate sounds, converting electrical energy to motional mechanical energy; in this capacity it is called a projector.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a hydroacoustic sound pickup. Hydrophones are electroacoustic transducers and are used in hydroacoustics to listen to underwater signals and noises, for measuring, and as a component of directional hydroacoustic receiving antennas. The most common hydrophones are based on electrodynamic, piezoelectric, and magnetostrictive effects. The operating principles of an electrodynamic hydrophone are the same as those of electrodynamic air microphones, except for the design features needed to protect them from water.

Piezoelectric hydrophones utilize the direct piezoelectric effect of crystals such as Rochelle salt, quartz, ammonium dihydrogen phosphate, and lithium sulfate, in which a variable deformation of a crystal creates variable surface electrical charges and a corresponding variable electromotive force (emf) at the electrode plates. Piezoelectric ceramics such as barium titanate and lead zirconate-titanate are widely used. The sensing elements of piezoelectric hydrophones are made in the form of rectangular or cylindrical packets.

Magnetostrictive hydrophones are based on the inverse magnetostrictive effect of certain ferromagnetic metals (mainly nickel and its alloys), in which a deformation produces a variable magnetic induction in the magnetic circuit and, consequently, a variable emf in the winding. The sensing elements of this type of hydrophone (the cores) are generally made of thin lamina in order to avoid the losses caused by eddy currents.

Hydrophones intended for measuring purposes should be nondirectional and have a flat frequency response over the entire range of frequencies being studied. To this end it is expedient to use hollow spherical receivers made of a piezoelectric ceramic that are small compared with the wavelength and that perform spherical symmetrical vibrations.

One of the most important characteristics of a hydrophone is its sensitivity, which is the ratio of the electrical voltage to the sound pressure, in microvolts per bar (μV/bar); it lies in the range from fractions of a μV/bar for small ceramic spherical receivers (several mm in diameter) to hundreds of μV/bar for packets of piezoelectric crystals. Preamplifiers that are mounted in the same housing as the receiver and are immersed in the water with it are used to increase the sensitivity, as well as to avoid the shunting effect of cable.


Tiurin, A. M., A. P. Stashkevich, and E. S. Taranov. Osnovy gi-droakustiki. Leningrad, 1966.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


(engineering acoustics)
A device which receives underwater sound waves and converts them to electric waves.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
"We were hoping when we put the hydrophone out we might hear a few sounds," Stafford, who first detected bowhead whales singing off Greenland in 2007, said. "When we heard, it was astonishing.
However, he stresses that, unlike using hydrophones for detection, the technology to transmit AGWs remains a major obstacle, not least because of the vast complexities created by applying this theory to the real world, but also because of the immense energy which would be required (the 2004 earthquake and subsequent tsunami generated more than 1,500 times the energy released by the Hiroshima atomic bomb).
Pro Sound Effects' latest library,Submerged,used a hydrophone to put together the collection of underwater sounds.
As a result, during the design and fabrication of acoustic devices, an optimized thin-film thickness can be utilized to control the frequency response characteristics of the hydrophone. This paper investigates the properties of diaphragm for the hydrophone applications in water, and to achieve this objective, the sensitivity of hydrophones is measured and the characterization of the mechanical properties are calculated.
After deciding on sound intensity, JRC Tokki needed to integrate Bruel & Kjaer hydrophones into their sophisticated underwater measurement system.
The boat was instrumented with an acoustic receiver (Model MAP_600 RT, Lotek Wireless) and stereo hydrophones (Model LHP, Lotek Wireless) capable of detecting, identifying, and recording CDMA transmitter signals.
Underwater noise is measured with an underwater microphone known as a hydrophone. The unit of measurement for underwater noise, or sound pressure level, is the same as for airborne SPL, the Pascal.
The Small Synthetic Aperture Minehunter system contains vertically spaced rows of hydrophones for interferometric (technique to extract arrival angle of acoustic waves) data processing.
The company's technology was developed for hydrophones used in detecting submarines.
But new analysis using data from underwater hydrophones also show an abrupt spike in seismic energy about 2.6 hours before the eruption started, which the scientists say could lead to short-term forecasting of undersea volcanoes in the future.
CMACS Ltd will place hydrophones into the water to listen for marine mammal acoustic activity both day and night.