A Highly Stable and Sensitive MEMS-Based Gravimeter for Long-Term Earth Tides Observations

Abstract

Precision measurements of local gravitational acceleration variations are of great importance in geophysical surveys. With advantages such as cost-effectiveness and portability, Micro-Electro-Mechanical system (MEMS)-based gravimeters have shown the potential for long-term gravity measurements. In this paper, aiming to further improve the stability of the instrument, the design considerations and system evaluations of a MEMS gravimeter are presented. With a linear spring design for the silicon proof-mass, a low natural frequency of ~14 Hz and a large linear range of ~10300 mGal are achieved with an ultra-low self-noise floor of 1.2 μGal/√Hz@1 Hz. By implementing a vacuum chamber system, the pressure variation is reduced from hundreds of Pa/day in atmosphere to a linear variation of ~6 Pa/day. In addition, an active temperature control system can suppress temperature fluctuations by 2 to 3 orders of magnitude within the band from 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> Hz to 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> Hz. The stability of the proposed MEMS gravimeter is demonstrated via long-term Earth tides observations within a 30-day time span, giving a correlation coefficient of 0.957 with the reference. An excellent bias instability of ≤4 μGal is demonstrated within the 8-3000 s averaging time range, representing one of the best performances to date in terms of stability for MEMS gravimeters. This shows the potential of high-performance MEMS gravimeters for petroleum and mineral prospecting, seismology and other geophysical applications.