A Wideband, Low-Noise Accelerometer for Sonar Wave Detection

Abstract

This paper presents the development of a high-performance micromachined capacitive accelerometer for detection of sonar waves. The device is intended to replace existing hydrophones in towed array sonar systems, and thus, needs to meet stringent performance requirements on noise, bandwidth, and dynamic range, among others. The in-plane, single-axis accelerometer is designed based on a mode-tuning structural platform. A frame was used instead of a solid plate for the proof-mass of the device, allowing us to push undesired vibration modes beyond the operating bandwidth of the device while enabling us to employ a portion of the area for capacitive sensing elements. The designed accelerometer was fabricated on a silicon-on-insulator wafer with 100- $\mu \text{m}$ device layer with capacitive gaps of $\sim 2.2~\mu \text{m}$ . The sensitivity of the accelerometer is 4 V/g with a noise spectral density of better than ${{350~{\mathrm {ng}}/}}\sqrt {\mathrm {{Hz}}} $ . The fundamental resonant frequency of the device is 4.4 kHz. The open-loop dynamic range of the accelerometer, while operating at atmospheric pressure, is better than 135 dB with a cross-axis sensitivity of less than 30 dB.