HYDROPHONE

Abhas mahawarEN 0936121001rrimt,lucknow

Overview

• Introduction and History• Working Principle• Piezoelectric Effect• Practical Implementation• Applications• Advantages & Disadvantages• Hydrophone vs. Sonar• Conclusion

Hydrophone?

Hydrophone (Greek

"hydro" = "water" and "phone" = "sound") is a microphone designed to be used underwater for recording or listening to underwater sound.

A "Hydrophone" is a device which will listen to, or pick up, the acoustic energy underwater, converts acoustic energy into electrical energy.

Hydrophones are usually used below their resonance frequency.

Most Hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure changes underwater.

History Hydrophone was used late in World War I. Naval Forces

used them to detect U-boats, greatly lessening the effectiveness of the submarine. Ernest Rutherford, in England, led pioneer research in hydrophones using piezoelectric devices. His only patent was for a hydrophone device.

How does it Work?Hydrophone device that receives

underwater sound waves and converts them to electrical energy.

There are special computer programs that

analyze these signals.

Further these signal can be read on a meter or played through a loudspeaker

PrincipleThe basic working principle is the

piezoelectric effect.

Hydrophones are being embedded with these piezoelectric transducers.

These transducer converts changes in water pressure into an electrical form.

Piezoelectric EffectThe conversion of mechanical

vibrations into electrical energy and vice-versa.

The active element is basically a piece of polarized material.

Affecting FactorThe factors affecting the working is acoustic impedance.

Acoustic impedance ( sound impedance) is a frequency dependent parameter.

Mathematically,

p denotes ‘sound pressure’.v denotes ‘particle velocity’.s denotes ‘surface area’.

Types of Hydrophones

Hydrophones are generally of two types

OMNIDIRECTIONAL HYDROPHONES which records sounds from all directions with equal sensitivity.

DIRECTIONAL HYDROPHONES which have a higher sensitivity to signals from a particular direction.

OMNIDIRECTIONAL HYDROPHONE

Omnidirectional Hydrophones BII-7000 are generally used in underwater vehicles AUV/UUVS & ROVS

Directional Hydrophones

FocusedIn this the hydrophone is held in a particular direction. To increase its sensitivity the receiving end must be spherical.

Arrayed HydrophoneIn this number of hydrophones are connected together to a single display unit. This pattern increases the efficiency.

Practical Implementation

Widely used in submarines and ships.

Helpful for naval defense services.

Detection of different sound wave frequencies.

APPLICATIONs

Acoustics release

Acoustics Fish Tags

Echo Sounder

AdvantageHydrophones does not require a power

source as they convert mechanical energy into electrical energy. Although other devices such as underwater cameras need a power source.

Underwater cameras are not as accurate as hydrophones because underwater cameras must be kept in an air-tight container

Disadvantages

Hydrophones can only listen to sounds and pressure differences.

Hydrophones are limited in their ability to distinguish between multiple objects or natural phenomenon and artificial noise

Set up requires time and space.

Comparison

Hydrophone is generally a unidirectional device while sonar is an omnidirectional device.

Not all hydrophones work as emitter but sonar works as a receiver and transmitter.

ConclusionThe technique is based on

piezoelectric effect.

A unidirectional device that can be further improved.

The technique can only be used in denser fluid because of the acoustic impedance matching.

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