Fiber Bragg grating seven-core hydrophone as an acoustic waves direction sensor

This study proposes an FBG 7-core membrane hydrophone capable of detecting low-frequency underwater sound waves and determining the resulting fiber bending direction. The hydrophone features a 3D-printed cylindrical shell with a latex membrane, to which the 7-core fiber is adhered at its center. Acoustic waves ranging from 50 to 400 Hz were generated using an underwater speaker, and Bragg wavelength shifts were recorded via a high-speed spectrum analyzer. Signal processing, including spectrograms, filtered wavelength shift-time representation, and Power Spectral Density analysis was applied to evaluate performance. The results revealed consistent signal patterns across cores, matching theoretical simulations and enabling bending direction determination. Experimental data confirmed that core-specific signal amplitudes align with the neutral axis orientation, and wavelength shift oscillations were used to calculate the curvature vector. The bending direction was determined to form a 64.09° angle with the reference axis. This work establishes a foundation for future three-dimensional directional determination of sound waves using Fiber Bragg Grating hydrophones.