Design and Implementation of a Quartz Cilia MEMS Vector Hydrophone.

Abstract

The cilium avoids energy loss due to bending deformation during vibration, thereby efficiently transmitting the acoustic driving force to the cross-beam. Meanwhile, a hollow cylindrical structure is adopted instead of the traditional solid one. While maintaining the same external geometry, this hollow design not only increases the effective acoustic area to enhance the acoustic driving force but also reduces the added mass of the cilium. This material-structure synergistic optimization improves the acoustic-to-mechanical transfer efficiency of the cilium in low-frequency acoustic fields, thus enhancing the device's acoustic sensitivity in the low-frequency range. Parametric simulations are conducted using the COMSOL Multiphysics 6.3 platform to systematically optimize key geometric parameters such as the outer radius and height of the quartz cilium, and the optimal dimensions are determined. The sensitivity and directivity of the prototype are measured in the 20-1000 Hz frequency range using the standard hydrophone comparison method. Experimental results show that the quartz cilium vector hydrophone achieves a sensitivity of -179.1 dB (1 kHz, 0 dB = 1 V/μPa) at 1000 Hz. The frequency response curve exhibits good flatness in the low-frequency range and agrees well with the theoretical 6 dB per octave increase characteristic of pressure gradient sensors. Directivity tests reveal a typical figure-8 pattern at both 315 Hz and 630 Hz, with null depths exceeding 30 dB, demonstrating excellent vector detection capability. This study provides an effective approach for improving the low-frequency sensitivity of MEMS (Micro-Electromechanical System) vector hydrophones, and the designed device meets the requirements for underwater target detection with promising prospects for engineering applications.