Hydrophone

A hydrophone or underwater microphone is an instrument used for detecting and recording underwater sound. They are usually sensitive to ultra-low frequency infrasound waves in the 10–100 Hz range (like elephant seals), to which human hearing is not sensitive. It can also detect higher frequency sounds such as snapping shrimp, dolphins, and marine mammals (whales, porpoises), seaquakes, geophysical sounds, weapons testing, and wind farm noise.

Detailed Hydrophone meaning

A hydrophone is a form of microphone invented to use underwater. It consists of a membrane that vibrates in response to sound waves, usually placed inside a cylindrical metal or plastic tube filled with water, attached to an amplifier, and converted into electrical signals which can be recorded on an audio device such as a computer. They are commonly used for acoustic research and by law enforcement agencies for covert surveillance applications. The term originates from Greek ὕδωρ (water) + φωνή (sound), as do seismic microphones, which pick up distant sounds through vibrations in a solid medium like soil.

Classification of hydrophones

Hydrophones can be classified into two categories: one for underwater use and another for airborne use. The underwater hydrophones are categorised as seismic, flow-through, and bottom. The surface hydrophones are divided into the dome, cupped, and bridge types. As we all know, hydrophones are used to detect sound in water; therefore, they need to be very sensitive. Most of them have a frequency range from 40 Hz to 20000 Hz, enabling them to detect sounds at different power levels and bandwidths. To understand what type of sound has been seen by our hydrophone or source, we must record and listen back with a decoder unit.

The hydrophones are also categorised as passive or active. The active hydrophones are of two types, a piezoelectric and a magnetostrictive. Piezoelectric hydrophones operate on pressure and electrical voltage changes, whereas magnetostrictive hydrophones operate on changes in magnetic flux density and electrical voltage. On the other hand, passive hydrophones have no power source; they only detect sound waves generated by ship propellers, explosions, cavitation bubbles, etc. Some of these passive devices can be used to measure background noise levels of coastal waters and infrasound related to distant thunderstorms or earthquakes. 

Advantages of hydrophone

A hydrophone is a scientific instrument used to detect underwater sound waves. Depending on its purpose, it can have various applications, such as monitoring aquatic ecosystems, studying marine life, detecting submarines, or underwater excavation activities. Its main feature is its ability to record distant and low-level sounds of interest at great depths in the water. 

Applications of hydrophones

Hydrophones are used for various purposes, ranging from locating submarines to tracking marine mammals. Some hydrophones are designed to measure oceanic conditions and can be permanently deployed in water columns. Hydrophones can also be placed underwater or in a target structure, such as an oil rig. 

Depending on its application, a hydrophone may be wired to a control room or have features that allow it to transmit information wirelessly. For instance, sound pressure levels in large tanks can be tracked via acoustic data transmitted through hydrophones placed inside or outside these tanks. 

During atmospheric studies or volcanic eruptions, scientists may also use hydrophones on land to gauge weather conditions and fine-tune their forecasts accordingly.

The other applications of hydrophones are as follows:

• Environmental monitoring
• Deep-sea operations
• Positioning and navigation systems
• Underwater exploration
• Towed arrays

Safety Precautions While using a hydrophone

Hydrophones have an excellent record; however, there are some situations in which they should not be used. They must never be immersed in water while mains electricity is connected, as both risk electric shock. A hydrophone is particularly sensitive to its surroundings. It may overload in areas where artificial sounds such as machines or vehicles are present, so a hydrophone may not always be ideal for a recording session. 

If you do use a hydrophone on your own, please remember that it should never be left unattended, and great care should be taken when it comes into contact with liquids; both factors could cause damage to your equipment. The cable of any microphone should not come into contact with other wires or metal surfaces if at all possible as these can cause electrical interference, which will affect sound quality.

Who invented the hydrophone?

Australian physicist William Henry Bragg & the New Zealand physicist Sir Ernest Rutherford conducted several experiments and invented hydrophones. Sir Ernest Rutherford holds the patent for the hydrophone. However, many claims state that Reginald Fessenden is the original inventor of the hydrophone.

Conclusion

The application and uses of the hydrophones are numerous. It has become helpful from military usage to studying and exploring marine life. We understood hydrophone meaning, its various usages, and the precautions to take while using the instrument. However, you can find varying answers if you search “which scientist invented hydrophone?” Nevertheless, this instrument has been aiding the human race for hundreds of years, and even in this digital era, hydrophones are used widely.