A μGal MOEMS gravimeter designed with free-form anti-springs
Shuang Wu, Wenhui Yan, Xiaoxu Wang, Qingxiong Xiao, Zhenshan Wang, Jiaxin Sun, Xiaobin Yu, Y. Yang, Qixuan Zhu, Guantai Yang, Zhongyang Yao, Ping Li, Chao Jiang, Wei Huang, Qianbo Lu
Abstract
Gravimeter measures gravitational acceleration, which is valuable for geophysical applications such as hazard forecasting and prospecting. Gravimeters have historically been large and expensive instruments. Micro-Electro-Mechanical-System gravimeters feature small size and low cost through scaling and integration, which may allow large-scale deployment. However, current Micro-Electro-Mechanical-System gravimeters face challenges in achieving ultra-high sensitivity under fabrication tolerance and limited size. Here, we demonstrate a μGal-level Micro-Opto-Electro-Mechanical-System gravimeter by combining a freeform anti-spring design and an optical readout. A multi-stage algorithmic design approach is proposed to achieve high acceleration sensitivity without making high-aspect ratio springs. An optical grating-based readout is integrated, offering pm-level displacement sensitivity. Measurements reveal that the chip-scale sensing unit achieves a resonant frequency of 1.71 Hz and acceleration-displacement sensitivity of over 95 μm/Gal with an etching aspect ratio of smaller than 400:30. The benchmark with a commercial gravimeter PET demonstrates a self-noise of 1.1 μGal Hz−1/2 at 0.5 Hz, sub-1 μGal Hz−1/2 at 0.45 Hz, and a drift rate down to 153 μGal/day. The high performance and small size of the Micro-Opto-Electro-Mechanical-System gravimeter suggest potential applications in industrial, defense, and geophysics. MEMS gravimeters are compact and cost-effective but face challenges in achieving ultra-high sensitivity due to fabrication tolerances and size limitations. Here, authors introduce a μGal MOEMS gravimeter with locally adjustable free-form anti-springs, achieving picometer-level displacement sensitivity.