Nano-g Micro-Optics Accelerometer With Force Feedback Control and Improved Dynamic Range

Optical sensing techniques are well-known for electromagnetic immunity and thus have been widely considered in high-performance vibration sensors such as accelerometers and seismometers. In the progress of miniaturization, however, the force feedback control has rarely been developed due to associated complexity of the optical loops. Aiming to further explore the application of interferometry in geophysics, a force-rebalanced micro-optics accelerometer is developed in this work. This device operates relying on a grating-based MEMS interferometer, where a 3D sensing structure is microassembled to serve as the moveable reflector. In the meantime, a soft robber magnet is arranged on the proof mass and then the feedback mechanism is constructed in combination with a wound coil. The open-loop test indicates this feedback system can generate a drive force of 43.39 nN/mA, and possesses a resultant displacement-regulating capacity of 20.7 nm/mA. Implemented with a digital PI control, the closed-loop device demonstrates an improved dynamic range of 1.012 mg, equal to 10 times of the open-loop state, along with a scale factor of 3250 V/g and a
$\text{R}^{{2}}$
coefficient of 0.99927. Additionally, the instrumental noise is tested as 10 ng/
$\sqrt {\text {Hz}}$
from 0.2 Hz to 10 Hz, and a bias stability of 36 ng is available at room temperature. Further considering the compact footprint of 4cm
$\times $
6cm
$\times $
3.15cm, this device exhibits great utility for microseismic observations in confined environments.