In this paper, micro-electromechanical systems (MEMS) technology and the bionic principle are used to develop a low-frequency high-sensitivity three-dimensional omni-vector hydrophone that can obtain vector information of an underwater sound field by imitating the auditory principle of a fish's lateral line organ. The key features are smaller size, better consistency, better low-frequency characteristic, higher sensitivity, and rigid mounting, which thus allow a spatial acoustic source to be detected directionally by a single hydrophone. The bionic MEMS microstructure was designed and fabricated and consists of two components: the vertical detection unit including a four-beam-cilium structure and a level detection unit including a double T-shaped beam structure. On the basis of theoretical analysis, the structure size and layout location of the piezoresistors are determined by simulation analysis and the double cilia type microstructure is fabricated integrally by MEMS manufacturing technology; after which the acoustic package of the microstructure is complete and the prototype is produced. Finally, this paper presents the experimental characterization of the microdevice, validating the concept and the analytical models used. The test results show that the three-dimensional vector hydrophone has a flat frequency response curve, exhibits a sensitivity of -185 dB (X, Y) and -181 dB (Z) (1 kHz, 0 dB reference 1 V/uPa) and shows a good directivity pattern in the form of an "8" shaped. More importantly, the depth of the concave point reaches 47.7 dB, and the asymmetry is only 0.5 dB, indicating that the three-dimensional vector hydrophone has great advantages in spatial orientation, which is suitable for applications in sonar systems.
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