Direction-Finding Study of a 1.7 mm Diameter Towed Hydrophone Array Based on UWFBG.

Area of Science:

• Ocean acoustics
• Fiber optic sensing
• Array signal processing

Background:

• Traditional hydrophones face limitations in sensitivity and directional accuracy for underwater acoustic detection.
• Developing compact, high-sensitivity hydrophone systems is crucial for advanced unmanned underwater vehicle (UUV) applications.

Purpose of the Study:

• To investigate the performance of a 1.7 mm diameter ultra-weak fiber Bragg grating (UWFBG) hydrophone towed array cable for acoustic direction finding.
• To demonstrate the directional response mechanism of the integrated-coating sensitizing optical cable for underwater acoustic waves.

Main Methods:

• An experimental setup using six sensing fibers coiled into 9 cm diameter rings was deployed in an anechoic pool.
• The response amplitude variation with sound wave direction was analyzed.
• Sensitivity measurements were conducted across a frequency range of 2.5 kHz to 6.3 kHz.

Main Results:

• The UWFBG hydrophone array demonstrated a directional response to underwater acoustic waves, with amplitude varying based on wave direction.
• An average sensitivity of -141.2 dB re rad/μPa was achieved within the tested frequency range.
• Azimuth detection of underwater acoustic waves was successfully validated.

Conclusions:

• The ultra-thin UWFBG towing cable system exhibits high sensitivity and underwater target-detection capabilities.
• The developed hydrophone array shows significant potential for future UUV-based acoustic sensing and navigation applications.
• The free structure and integrated-coating sensitizing optical cable design contribute to its effective performance.