Hydrophones usually are used to detect and measure sound waves in aquatic environments. The sensitivity of a hydrophone refers to its ability to detect low-intensity sound signals. Essentially, it measures how effectively the hydrophone can pick up weak acoustic signals from the surrounding water. Hydrophone is necessary for a range of applications such as marine biology, sonar systems, underwater communication, and seismic research.
What is Hydrophone Sensitivity and How is it Measured?
Understanding Hydrophone Sensitivity
Hydrophone sensitivity refers to the amount of output signal (usually in volts) produced by the hydrophone in response to an incoming sound pressure, measured typically in micro Pascals (µPa). Essentially, it quantifies how efficiently the hydrophone converts underwater sound pressure into an electrical signal. The unit of sensitivity is often expressed as volts per microPascal (V/µPa), which helps to characterize the sensor’s response to sound waves.
Factors Affecting Hydrophone Sensitivity
- Frequency Response: Hydrophones are frequency-dependent, meaning their sensitivity varies across different frequency ranges.
- Size and Shape:The physical characteristics of the hydrophone, such as its size and design, can affect how effectively it captures sound. A larger hydrophone typically picks up a broader range of frequencies and may have better low-frequency sensitivity. It is a superb thing if a hydrophone is small in size but has high sensitivity as well as large frequency responses range.
- Environmental Conditions: The surrounding environment, such as water salinity, temperature, and pressure, can significantly alter the hydrophone’s sensitivity. Calibration in specific conditions is necessary for accurate measurements.
- Miniature Hydrophone which has high sensitivity and large frequency responses range: https://www.seis-tech.com/miniature-hydrophone-ys-3000/
- Much smaller size of YS-3000 Piezo sensor with same capability also available.
How is Hydrophone Sensitivity Measured?
To measure the sensitivity of a hydrophone, a common method involves using a reference hydrophone. Here’s a general approach to measuring the receiver sensitivity:
- Set Up a Calibration Environment: The measurement takes place in an acoustically controlled environment, such as a tank or a hydroacoustic basin. The hydrophone is submerged, and a calibrated transducer emits a known sound pressure level.
- Use a Reference Hydrophone: A reference hydrophone with a known sensitivity is placed in the same environment. It captures the sound pressure from the transducer. The output voltage from the reference hydrophone is recorded.
- Replace with Unknown Hydrophone: After recording data from the reference hydrophone, the unknown hydrophone is placed in the same position, and the same sound pressure is applied. The output voltage of this hydrophone is recorded.
- Calculate Sensitivity: The sensitivity of the unknown hydrophone is calculated relative to the reference hydrophone by comparing their voltage outputs. This process may include adjusting for environmental factors like reflected sounds or background noise, which can skew results.
Practical Considerations in Measuring Sensitivity
- Calibrated Microphone vs. Hydrophone: In some cases, using a calibrated microphone to measure the sensitivity in air can be an alternative, especially when dealing with low-cost or smaller-frequency applications. However, this may not be ideal for very high-frequency hydrophones or those meant for specialized underwater tasks.
- Environmental Noise: Calibration tests must account for ambient noise in the testing environment, as even low levels of extraneous noise can impact the accuracy of sensitivity measurements.
- Frequency Range: Different hydrophones are designed for specific frequency ranges, with some being more sensitive to low frequencies and others to high frequencies.
Conclusion
Hydrophone sensitivity is a fundamental characteristic that determines the capability of a sensor in detecting underwater sounds. Accurate measurement requires controlled conditions, appropriate calibration, and careful analysis of the hydrophone’s response to various acoustic pressures. When measuring hydrophone sensitivity, understanding how environmental factors influence the sensor’s behavior is key to obtaining reliable data.
Referral
- R. J. Bobber,Hydroacoustic Measurements [Russian translation], Mir, Moscow (1974).
- M. Janneh et al. Field demonstration of an optical fiber hydrophone for seismic monitoring at Campi-Flegrei caldera，Opt. Laser Technol. (2023)
- D.Kim et al. Development of a high-performance cymbal vector hydrophone Sens. Actuators A: Phys. (2024)
- G.R. Harris et al. Interlaboratory evaluation of hydrophone sensitivity calibration from 0.1 to 2 MHz via time delay spectrometry，Ultrasonics (2004)
