A Very Low-Frequency 3-D Vector Hydrophone Based on an Electrochemical Vibration Sensor

Typically, hydrophones are used to monitor hydroacoustic signals generated by ocean activity. However, it is challenging to achieve detection in the lower frequency bands with existing hydrophones due to their low sensitivity in the tens of hertz range. A very low-frequency (VLF) 3-D vector hydrophone with a co-oscillating sphere based on an electrochemical vibration sensor is developed in this article. The vibrations caused by the acoustic waves are transmitted to a triaxial electrochemical vibration sensor inside the co-oscillating sphere, where it is converted into current signals by the electrochemical reaction of the sensitive electrodes. The theoretical analysis and numerical simulation conducted have effectively revealed the principles of the electrochemical hydrophone and obtained the influence of critical parameters on performance. Sensitive electrodes fabricated by microfabrication technology were assembled into electrochemical sensors encapsulated in the vector hydrophone. The characterization results showed that the hydrophone featured a low working frequency band of 0.8–100 Hz after low-frequency compensation and a high sensitivity of -180 dB (ref. 1 V/ $\mu $ Pa) within the bandwidth. The concave point depth of eight-shaped directivity was beyond 30 dB. The noise floor was below or near the sea state 0.