What is an Hydrophone?

A hydrophone is an underwater sensor designed to acquire sounds, noises and other acoustic signals that propagate in the sea or in fresh water. Just as microphones are used to detect acoustic waves in gaseous environments (the earth’s atmosphere), hydrophones are used to detect sounds that propagate in liquid environments. 

The study of the propagation of sounds in the marine environment, whether they are subsonic or ultrasonic, and the technology, developed in the military field starting from the First World War, have subsequently been extended, being applied for civil applications of various types and bioacoustics, as for example for the acoustic monitoring aimed at the protection of seas and cetaceans. 

The hydrophones are studied and designed according to the different applications to which they are dedicated. They consist of a sensitive part made of piezoelectric ceramic and, in some cases, also of an electronic part capable of amplifying the acquired and / or transmitted signal. 

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They can be designed as passive sensors (hydrophones), suitable only for listening and therefore for the acquisition of acoustic signals, or as active sensors (transducers) capable not only of receiving but also of emitting acoustic signals. 

According to the type of application and the consequent acoustic parameters, therefore, different characteristics of the piezoelectric ceramics and different settings of the electronic part are defined. More sensitive hydrophones are able to measure very low intensity sounds even at considerable distances (depending, however, on the level of ambient noise), since the sound in the sea propagates with a speed 5 times higher than in the air.

For this reason, the intrinsic quality of hydrophones and their electronics is directly proportional to their “noise”. The more a hydrophone will be “silent” and its intrinsic noise under the sea noise curve, the more it will be sensitive and able to acquire small signals emitted even at very considerable distances. Ultra silent hydrophones are those with an intrinsic noise curve under the zero force sea noise curve (the so-called “below sea state zero” hydrophones).

The fields of application, as we said, are different: from marine bioacoustics to military applications, passing through applications of geophysics and research in the oil and gas sector. In general it can be said that where an acoustic signal has to be studied in a “liquid” environment, the presence of one or more hydrophones and / or transducers is necessary.

For some bioacoustics and environmental monitoring applications, for example, acoustic signals emitted by cetaceans and environmental noises of various types are monitored. These, if acquired by an array of hydrophones in a known position, can  be processed through special “signal processing” algorithms, to determine the direction of arrival of the signal and other parameters of interest.

Hydrophones and transducers application fields vary from “shallow waters” to extreme environments and ultra-deep waters. For i.e. Colmar has recently developed digital hydrophones for a project regarding the study of Neutrinos, using arrays positioned at a depth of 3500m.

Finally, the use of hydrophones can be find also in the industrial field, for example for the monitoring of pump or other equipment inside tanks, in order to prevent malfunctioning and extend the obsolescence of such equipment.

Characteristics of a hydrophone?

Hydrophones are made of a piezoelectric ceramic, which translates the mechanical energy resulting from the impact of the acoustic pressure wave into electrical energy. This happens because sound is nothing more than a change in pressure in a fluid. Some hydrophones can also be used as emitters as well as receivers, in this case we talk about transducers. 


Underwater acoustics with related  sonar and  passive listening hydrophone systems start to develop in the last century, coinciding with the two world wars, when all the navies invested large sums for the development of discovery and localization underwater equipment to be installed on ships, airplanes, submarines or arrays to be anchored on the seabed, in order to identify the presence and passage of enemy submarines (ASW Anti Submarine Warfare)

What do we do

We produce a wide range of hydrophones and transducers as well as more complex acoustic systems, suitable for both oceanographic research and environmental monitoring. Filed of application extends from the military to the environmental sector passing through the oil and gas sector where we have always operated all over the world with our patented “ALD” (Acoustic Leak Detector) system for subsea leak detection on pipelines.

In addition to the standard range of hydrophones and transducers, we design and develop custom products on customer request. Our headquarter is equipped with a large tank where we can carry out acoustic tests and calibrations in a controlled environment. We are also equipped with several pressing chambers where we can test our tools by simulating hydrostatic pressures up to 4000m of depth.

Recent projects also see us engaged in the study and construction of autonomous systems for leak detection on pressurized pipes containing.