Low-Cost, High-Sensitivity Hydrophone Based on Resonant Air Cavity

Underwater acoustic ranging and detection usually require hydrophones to have high sensitivity at narrowband operating frequencies. Different from traditional sensitization methods with the help of new materials and solid/liquid resonance structure, this paper proposes a low-cost, high-sensitivity hydrophone based on a resonant air cavity containing an affordable MEMS microphone inside to sense the focused acoustic waves transmitted from the external water across the solid shell into the air cavity. Both finite element simulations and experiments are carried out to test its acoustic sensing performances. Resonance frequency and directivity of the proposed hydrophone are determined by the air cavity size and the acoustic mode, but is independent of the solid shell, which facilitates the precise designability. The sensitivity of the developed hydrophone at the resonance frequency is up to -157 dB re 1V/$\mu $ Pa calibrated by commercial standard hydrophone TC4013. Finally, several further considerations, improvements and applications on the proposed hydrophone are discussed.