Broadband hydrophone ZET 321 (BC 321)

  • reversible hydrophone without an integrated amplifier;
  • can be used as receiver and transmitter;
  • research of low-power signals in a wide frequency range;
  • research of long-distance acoustic signals propagation;
  • available versions of the product: submersible or threaded.

Price on request



of broadband hydrophone ZET 321 (BC 321)

Technical specifications
Item ZET 321
Product version submersible threaded
Nominal sensitivity by voltage 22 µV/Pa 22 µV/Pa
Nominal sensitivity by charge 0,12 pC/Pa 0,1 pC/Pa
Frequency range 3…160 000 Hz
Maximal static pressure* 60 MPa
 Capacity (without cable) not less than 2 nanofarad
Casing material stainless steel
Dimensions (length × casing diameter) 173 × ⌀23 mm 171 × ⌀20 mm
Connection thread M20×1,5
Weight (without cable)
Cable length (standard) 10 m 2 m
Maximal cable length 40 m
Environment of measurements performance water, air, oil and petrochemicals, natural gas
Operating environment temperature 0…+60 °С
Ambient air temperature −60…+80 °С

*The limiting hydrostatic pressure is indicated for the receiving element of the hydrophone and can be limited by the technical characteristics of the cable, in the case of immersion studies.


of broadband hydrophones ZET 321 (ВС 321)


  • of sound propagation in water;
  • of ultra-sound in liquid environment;
  • of noise in moist and polluted environments;
  • of sound in liquid and gaseous environments (for laboratory and factory use).

Application scenarios

  • as a reference calibration instrument;
  • as an instrument used for sound emission;


  • of marine mammals vocalization
  • of cavitation processes

Installation requirements

for threaded hydrophone ZET 321 (BC 321)

The hydrophones should be installed in special mounting areas (transition adapters, hot tapping, etc.).

The hydrophone should be installed into the mounting area with the use of wrench and hexagonal section of the measurement unit. Other parts of the hydrophone should not be used for installation purpose.

In order to secure hermeticity of hydrophone installation, it is necessary to use the sealing end (copper gasket), which is included into delivery scope. It is undesirable to use other types of end sealing (e.g., foam tape, flax fiber, etc.), since these types of sealing are not able to provide the required level of hermeticity.

Hydrophone BC 321 by ZETLAB - dimensional drawing of the mounting surface

Mounting section layout

Installation scheme for threaded hydrophone by ZETLAB

Example of threaded hydrophone installation

Connection scheme

of the broadband hydrophones ZET 321 (ВС 321)

Hydrophones ZET 321 (ВС 321) are connected to the FFT Spectrum analyzers via charge amplifiers ZET 420 (used for signal emission) and ZET 440 (used for measurement performance).

Use of hydrophone for signals emission - Connection scheme

Use of hydrophone for measurements performance - Connection scheme

Use of ZETLAB hydrophones for signals emissions - connection scheme

Use of ZETLAB hydrophones for measurements performance - connection scheme

Operation of hydrophones in the mode of signals receipt and emission

The below graph shows the AFR of hydrophone  ZET 321 in the signal receipt mode.

Hydrophone BC 321 by ZETLAB - AFR unevenness graph

Broadband hydrophone ZET 321 can be used for sound emission and for measurements of sound propagating in liquid environment. Piezo-electric sensing element of the hydrophone has a reversibility effect. Mechanical oscillations lead to generation of electrical signal, and vice versa: alternating current applied to the sensing element results into mechanical oscillations. In the graph, you can see frequency characteristic of broadband hydrophone ZET 321, and the frequency characteristic of BC 311 operating in the signal emission mode (for comparison purpose).

Hydrophone BC 321 by ZETLAB - characteristics in the signals emission mode
Frequency characteristics of  ZET 321 and BC 311 in the signal emission mode,
dB in relation to 1 µPa/V per 1 m

Application scenarios

of the broadband hydrophones ZET 321 (BC 321)

The hydrophone is represented by piezo-electrical transducer with the sensing element made from ceramic piezo-electrical materials. The sensing element and its inner bearing structure are firmly fixed inside of sound-proof package (duprene rubber is used as the material of the package). The main casing is made of stainless steel, which is resistant to corrosion, negative environmental impact, and can also be used in seawater. All steel components of the hydrophone have the required protection.

Hydrophone ZET 321 has smooth frequency response curve throughout the entire frequency range in the case if it is used in homogeneous environment (including air, sea and fresh water).

Acoustic-research-of-marine-mammals Acoustic communication is an important component in the life of the cetaceans. Noise pollution of the ocean (sonar systems, underwater explosions, and water traffic) is the main reason of marine mammals population reduction, since the noise negatively affects hearing system of the cetaceans. Broadband hydrophones ZET 321 (BC 321) can be used as a primary transducer of acoustic pressure in measurement and recording systems for marine mammals research.

Acoustic detection devices based on the use of hydrophones ZET 321 allow to find the exact location of vocalizing marine mammals as well as to record the sounds produced by dolphins and whales.

This method can be considered to be the most ecologically safe one, since the acoustic detection devices located on the seabed do not disturb the marine animals, while the data obtained with the use of such systems is quite sufficient for exact detection of the sound source location.

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