A Compliant Mandrel-Based Fiber-Optic Hydrophone for Underwater Acoustic Sensing

This article presents the design, numerical modeling, and experimental validation of a mandrel-based fiber-optic hydrophone (FOH) tailored for underwater acoustic sensing. The hydrophone leverages a compliant mandrel structure to transduce radial pressure-induced strain into axial strain along an optical fiber wound around the mandrel, with acoustic signals retrieved via interferometric techniques. A comprehensive 3-D finite element model is developed to evaluate the mechanical response and sensitivity characteristics of the hydrophone. Experimental validation is conducted in a water tank using a calibrated piezoelectric transducer, confirming the simulated predictions. The designed FOH exhibits a mean acoustic pressure sensitivity of -135.28 dB re rad/$\mu $Pa over the frequency range of 250 Hz–8 kHz, which is competitive with state-of-the-art FOH designs reported in recent literature. The pressure noise floor characterization yielded a value of 43.28 dB re rad2/Hz at 1 kHz, demonstrating the hydrophone’s capability to detect weak acoustic signals below deep-sea state 0 (DSS0) up to frequencies above 1 kHz. The results suggest that this mandrel-based FOH design offers a robust, scalable, and cost-effective solution for large-scale underwater acoustic monitoring systems, with strong potential for integration into fiber-optic sensor arrays used in oceanographic, industrial, and defense applications.