A Seismic-Grade Optical MEMS Accelerometer with Force Feedback Control

This work presents design, fabrication and experimental demonstration of a high-resolution optical Micro-Electro-Mechanical Systems (MEMS) accelerometer applicable to microseismic observations. This device employs a deformable grating based interferometer to transduce tiny accelerations into variations of light intensity. A low-frequency Z-axis-sensitive MEMS sensing structure, which has a three-dimensional (3D)-suspension design, is fabricated to serve as the deformable element. The mechanical and optical modules are both assembled into a small-size accelerometer prototype, featuring compactness and portability. In order to enlarge the limited dynamic range, a force feedback mechanism and the dedicated control loop are developed. A series of experiments are then carried out to verify the sensor functionalities. It is proved that a measurement range of 1.012 mg has been achieved with a voltage sensitivity of 3250 V/g and a linear coefficient (R
²
) of 0.99927. Additionally, the inherent microseismic peaks of Earth are tracked by this device, demonstrating a low instrumental noise of 10 ng/√Hz from 0.2 Hz to 10 Hz.