A hydrophone (Greek "hydro" = "water" and "phone" = "sound") is a microphone designed to be used underwater for recording or listening to underwater sound. Underwater acoustics is the study of the propagation of Sound in Water and the interaction of the mechanical waves that constitute sound with the water and its boundaries Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change. Piezoelectricity is the ability of some materials (notably Crystals and certain Ceramics including bone to generate an Electric potential in response to A transducer is a device usually electrical, electronic, Electro-mechanical, Electromagnetic, Photonic, or Photovoltaic Such piezoelectric materials, or transducers can convert a sound signal into an electrical signal since sound is a pressure wave in fluids. A transducer is a device usually electrical, electronic, Electro-mechanical, Electromagnetic, Photonic, or Photovoltaic Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies Some transducers can also serve as a projector (emitter), but not all have this capability, and may be destroyed if used in such a manner. An emitter is a device used to emit any signal, Beacon, Light, Odor, Liquid, Fragrance, or any other type of

A hydrophone can "listen" to sound in air, but will be less sensitive due to its design as having a good acoustic impedance match to water, the more dense fluid. The acoustic impedance Z (or sound impedance) is a frequency f dependent parameter and is very useful for example for describing the behaviour of musical Likewise, a microphone can be buried in the ground, or immersed in water if is put in a waterproof container, but will give similarly poor performance due to the similarly bad acoustic impedance match.

Contents 1 History 2 Directional hydrophones 2.1 Focused Transducers 2.2 Arrays 3 See also 4 References 5 Links

History

The hydrophone was used late in World War I. World War I (abbreviated WWI; also known as the First World War, the Great War, and the War to End All American convoys used them to detect German U-boats, greatly lessening the effectiveness of the submarine. Ernest Rutherford, in England, led pioneer research in hydrophones using piezoelectric devices. Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist His only patent was for a hydrophone device.

Directional hydrophones

A small single cylindrical ceramic transducer can achieve near perfect omnidirectional reception. A transducer is a device usually electrical, electronic, Electro-mechanical, Electromagnetic, Photonic, or Photovoltaic Directional hydrophones increase sensitivity from one direction using two basic techniques:

Focused Transducers

This device uses a single transducer element with a dish or conical-shaped sound reflector to focus the signals, in a similar manner to a reflecting telescope. A transducer is a device usually electrical, electronic, Electro-mechanical, Electromagnetic, Photonic, or Photovoltaic This type of hydrophone can be produced from a low-cost omnidirectional type, but must be used while stationary, as the reflector impedes its movement through water.

Arrays

Multiple hydrophones can be arranged in an array so that it will add the signals from the desired direction while subtracting signals from other directions. In Computer science an array is a Data structure consisting of a group of elements that are accessed by indexing. The array may be steered using a beamformer. Most commonly, hydrophones are arranged in a "line array" but may be in two or three dimensional arrangements.

See also

• Communication with submarines
• underwater acoustics
• sonar

References

• Pike, John (1999). Communication with submarines when they are submerged is a difficult technological task which requires specific techniques and devices Underwater acoustics is the study of the propagation of Sound in Water and the interaction of the mechanical waves that constitute sound with the water and its boundaries Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate SOSUS Retrieved Jan. SOSUS, an acronym for SOund SUrveillance System, was a chain of underwater listening posts located across the northern Atlantic Ocean 28, 2005.
• Watlington, Frank (1979). How to build & use low-cost hydrophones. (ISBN 0830610790)
• Unknown. hydrophone Retrieved Jan. 28, 2005.
• Unknown. (2005) Schlumberger Oilfield Glossary: Term 'hydrophone' Retrieved Jan. 28, 2005.

Links

• DOSITS Hydrophone introduction at Discovery of Sound in the Sea
• orcasound.net Live hydrophone streams from killer whale habitat
• Passive Acoustic Monitoring Using hydrophones to monitor underwater sounds
• Build your own hydrophone (free instructions)
• Build your own hydrophone #2 Online tutorial at the freesound project.
• Hydrophone recordings at the freesound project.
• Precision Acoustics useful resource on hydrophones

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