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 microphonedesigned to be usedunderwater for recording orlistening 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. Most Hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure changes underwater. Hydrophones are usually used below their resonance frequency.
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
Principle The 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 Effect The conversion of mechanical vibrations into electrical energy and vice-versa. The active element is basically a piece of polarized material.
Affecting Factor The 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 particulardirection. To increase its sensitivity thereceiving end must be spherical.
Arrayed HydrophoneIn this number of hydrophones are connectedtogether to a single display unit. This patternincreases 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
Advantage Hydrophones 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.
Conclusion The 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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