Primary calibration of ultrasonic hydrophone using optical interferometry

Area of Science:

• Acoustics
• Metrology
• Optical Engineering

Background:

• Accurate calibration of ultrasonic hydrophones is crucial for underwater acoustics and sonar applications.
• Existing calibration methods may have limitations in accuracy or frequency range.
• A primary calibration method provides a fundamental reference for hydrophone sensitivity.

Purpose of the Study:

• To develop and validate a primary calibration method for ultrasonic hydrophones.
• To determine the free-field sensitivity of hydrophones in the 0.5-15 MHz range.
• To assess the accuracy and uncertainty of the proposed calibration technique.

Main Methods:

• Utilized a Michelson interferometer to measure particle displacement in an ultrasonic field.
• Derived acoustic pressure from particle displacement measurements.
• Determined hydrophone free-field sensitivity based on acoustic pressure and displacement.
• Investigated and corrected for optical detection system frequency response.
• Accounted for various acoustical effects within the calibration procedure.

Main Results:

• Achieved a primary calibration method for ultrasonic hydrophones with typically 1% random uncertainty.
• Systematic uncertainty ranged from 2.3% to 6.6% across the 0.5-15 MHz frequency range.
• Calibration results demonstrated agreement with other established methods and theoretical predictions.
• Successfully used the method to assess hydrophone temporal stability over two years.

Conclusions:

• The Michelson interferometer-based method provides a robust primary calibration for ultrasonic hydrophones.
• The method offers high accuracy and reliability for determining hydrophone sensitivity.
• This technique is suitable for evaluating hydrophone performance and long-term stability.