Design and characterization of a magnetostrictive hydrophone for low-frequency, low-noise underwater acoustic sensing

This study presents the design, modeling, and experimental characterization of a magnetostrictive hydrophone capable of operation up to 5 kHz, below its fundamental mechanical resonance. The transducer incorporates a Terfenol-D core within a compliant, magnetically permeable steel housing that provides both mechanical prestress and tunable compliance through Belleville washer assemblies. To enable calibration without reliance on large open-water facilities, a tank-based measurement method is developed using burst-tone excitation and post-excitation ringdown analysis, which effectively eliminates electromagnetic interference. The measured sensitivity exhibits the expected +6 dB/octave increase with frequency below resonance and agrees closely with finite-element simulations and a reduced-order network model. The minimum detectable pressure, estimated from the modeled self-noise and sensitivity, remains below the Sea State 0 noise floor and is projected to outperform a commercial reference hydrophone across the sub-resonant band. These results confirm the viability of magnetostrictive transduction for low-noise underwater acoustic sensing. To the best of our knowledge, this work reports the first realization and validation of a hydrophone based on giant magnetostrictive materials, extending their application beyond power projection to precision underwater sound detection.