Measurement of Earth Tides with a MEMS Gravimeter via Releasing the Axial Force of Cross-Configured Geometric Anti-Spring

Gravimeters play an important role in geophysical research, including mineral prospecting, hazard forecasting, and crustal deformation monitoring. However, existing commercial gravimeters are typically bulky and expensive. MEMS gravimeters incorporating geometric anti-spring (GAS) mechanism effectively address these limitations and exhibit high sensitivity and low resonant frequency. In this work, we employ finite element analysis to investigate the relationship between the stiffness characteristics of the GAS and its axial force. Through this analysis, we propose a novel design that adopts a crossed configuration of two sets of GASs with different dimensions, enabling the proof mass to displace both along and perpendicular to the sensitive axis. This configuration effectively reduces the axial forces in the shorter-arc-length GAS and mitigates the spring system’s negative stiffness effect. By optimizing the dimensions of GASs, the quasi-zero stiffness characteristic can be achieved. A low-cost, low-noise optical shadow displacement sensor is designed to detect the displacement of the proof mass. A five-day measurement of Earth tides reveal that the experimental data has a correlation coefficient of 0.91 with the theoretical date from the TOSFT software. Final tests demonstrate that the MEMS gravimeter achieves a noise power spectral density of 5 μGal/√Hz at 3 Hz.