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Underwater microphone
We all know what a microphone is. It is a device that serves to receive, amplify or record sound on various media. But this is to record ordinary sounds, such as human speech or the barking of a dog.
Suppose we want to hear the “voices” of mammals, fish, and other aquatic life, such as shrimp. If we set the microphone above the very surface of the water, we will not be able to record anything but irrelevant noise. Most of these sounds will remain underwater – they won’t enter the air above them. For the microphone to work, we must lower it into it must be submerged.
But wait a moment. An ordinary microphone will “choke” in water: the membrane will be saturated with water, the electrical circuit will fail, and you will ruin your device. What is needed is a specially designed microphone – an underwater microphone or a hydrophone: a hydroacoustic sound receiver.
what are hydrophones used for?
The oceans and many freshwater locations are “bubbling” with sounds. In seawater, sound travels five times faster than in the air: in water, its speed is 1500 m/s, while in the air, it is only 300 m/s
The sounds of the sea can be heard through a hydrophone. It amplifies sounds and makes them clearer. A hydrophone can be suspended in the water column, placed on the sea floor, or fixed on the underwater part of a ship. With the help of a hydrophone, you can hear the splashing of water, splashes of the surf, sounds of engines and propellers of ships passing in the distance, and the noise from fish, whales, dolphins, seals and other aquatic life. In addition to listening to underwater signals and noise, hydrophones are used for measuring purposes and also as components of directional receiving hydroacoustic antennas or arrays.
Hydrophone frequency range
Hydrophones have a rather diverse design and technical characteristics depending on the purpose. They generally cover the frequency range from 0.1 Hz (for perceiving and measuring infrasonic waves propagating hundreds and even thousands of kilometres in water) to 500 kHz (for high-precision ultrasonic location). Hydrophones can be designed to operate at various depths, including some that are rated for over 10,000 meters for the deepest parts of our oceans.
The frequency range at which these devices work depends on their sensitivity, which is proportional to the area of the sensor. This means that when a hydrophone is too sensitive with respect to the measured field, it can be saturated. When there is insufficient sensitivity, we can have a noise limit in the measurements so that the noise can mask the underlying acoustic signal.
How do hydrophones work?
The mechanical action, or pressure, exerted by a sound wave on the material of the hydrophone sensing element causes electrical charges to appear on the material’s surface and, consequently, a change in the charge distribution in the material causes a voltage change.
Therefore, a hydrophone measures the pressure changes underwater, which depend on the frequency, speed and distance at which the sound wave travels. When these pressure changes come in contact with the hydrophone, it transmits the electric charge fluctuations due to the voltage variation through the electric cable.
To increase sensitivity (as well as to eliminate the cable drift effect), you can use a hydrophone with an integral preamplifier.
Hydrophone construction
Hydrophones are encased in a ruggedized housing to protect them from seawater and corrosion.
In order to protect the electrical parts, it is very important that the connection between the hydrophone and cable is watertight.
Most hydrophones are manufactured with a piezoelectric material as these are characterized by their excellent electrical properties, allowing them to give excellent frequency responses. Piezoelectric are materials that change their shape and generate small electrical charges in response to the pressure changes they experience.
Hydrophone Specifications
Hydrophone Sensitivity
In this case, what is being measured is the receiving sensitivity, the amount of voltage that a given sound produces. You will find it as (dB re 1 V at 1 Pa), which is read as a decibel relative to 1 volt per 1 pascal.
Since no sound generates that much voltage in a hydrophone, the measurements are expressed negatively. Thus, if you read that a hydrophone has a sensitivity of -195 dB re 1 V at 1 Pa, it means that it is less powerful than another one with a sensitivity of -190 dB re 1 V at 1 Pa.
Why is sensitivity measured and not power?
Humans do not perceive changes in sound proportionally to their power but logarithmically. A 10 dB increase produces a 10-fold increase in sound intensity and doubles the increase in perceived sound volume. the sound pressure level in a typical office area at night will be about 40 dB since no one is working or circulating in the area, and in the daytime, with heavy traffic, it may be 70 dB. This equates to a 1,000 times increase in sound intensity and an eight times increase in perceived volume.
Capacitance
Capacitance refers to an element used to store energy in the form of an electrostatic field or the ability of such an object to store such electric charge expressed as a quantity, for instance, nanofarads (nF).
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professional Grade hydrophones
What we offer
Hydrophones and portable calibrator
Summary of information
on all hydrophones.
The calibrator validates
hydrophones sensitivity before deployment.
M15-900
Max. Depth (m): 900
Max Frequency (Hz): 15,000
Unamplified Sensitivity (dB re V/μPa): -190
Element Capacitance (nF): 1
M14-900
Max. Depth (m): 900
Max Frequency (Hz): 20,000
Unamplified Sensitivity (dB re V/μPa): -200
Element Capacitance (nF): 8
M5-900
Max. Depth (m): 900
Max Frequency (Hz):20,000
Unamplified Sensitivity (dB re V/μPa): -195
Element Capacitance (nF): 2
M36-900
Max. Depth (m): 900
Max Frequency (Hz): 250,000
Unamplified Sensitivity (dB re V/μPa): -200
Element Capacitance (nF): 1.5
M15-360
Max. Depth (m): 1,700
Max Frequency (Hz): 15,000
Unamplified Sensitivity (dB re V/μPa): -190
Element Capacitance (nF): 1
M5-360
Max. Depth (m): 1,700
Max Frequency (Hz): 20,000
Unamplified Sensitivity (dB re V/μPa): -195
Element Capacitance (nF): 2
M36-100
Max. Depth (m): 2,500
Max Frequency (Hz): 250,000
Unamplified Sensitivity (dB re V/μPa): -200
Element Capacitance (nF): 1.5
M14-360
Max. Depth (m): 3,500
Max Frequency (Hz): 20,000
Unamplified Sensitivity (dB re V/μPa): -200
Element Capacitance (nF): 5
Rising Tide BioAcoustics is a worldwide authorized distributor of GeoSpectrum Technologies Inc. commercial transducers for environmental and bioacoustics applications. The products we commercialize are listed at the bottom.