A portable and high-resolution optomechanical accelerometer employing a deformable grating-based micro-electro-mechanical system (MEMS) interferometer is presented in this Letter. The movable reflective mirror of this interferometer is realized by a low-frequency vertical sensing structure with a three-dimensional (3D)-spring construction, which, to the best of our knowledge, is first proposed and fabricated in this work. All the components of the sensor are packaged in a metal case with a compact size of 4 cm×6 cm×3.15 cm. The micrometer-scale springs permit the device to have a high mechanical sensitivity of 893.23 µm/g and a resultant self-noise below 2 n g / H z from 2 to 7 Hz. Meanwhile, the measured voltage responsivity is as high as 15,874 V/g, demonstrating it is one of the most sensitive accelerometers reported to date.

Traditional seismometers and gravimeters normally have large volumes and entail high manufacturing costs. Aiming at the miniaturization of such geophysical instruments, a portable microelectromechanical systems (MEMS) accelerometer applicable to seismic-grade measurements is fabricated and characterized in this work. This accelerometer is operating on the deformable grating-based MEMS interferometer, where a new MEMS out-of-plane sensing chip employing double layers of 10- $\mu \text{m}$ -thickness spring is first proposed. The simulation results show that this geometry has a low natural frequency of 52.23 Hz and undergoes a low stress of 26.94 MPa under the gravitational acceleration. The test of the fabricated prototype is implemented in a quiet environment for tracking the inherent microseismic peaks of Earth. The evaluation results demonstrate that the fabricated prototype has achieved a voltage sensitivity of 510.6 V/g. Furthermore, the noise estimation indicates that the self-noise of this sensor has reached 20 ng/ $\sqrt {\text {Hz}}$ from 0.3 to 20 Hz, and a bias stability of 235.4 ng is obtainable at room temperature. Combined with the compact package size of 40.5 cm ³ , the proposed device exhibits a promising prospect in the seismic-grade applications.

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.

Optical microelectromechanical system (MEMS) devices are often used to measure vibrations with exceedingly small amplitudes, which are extensively used in acceleration and seismic sensors. However, owing to the limitations of the sensing principle and the variation in ambient temperature, the measurement accuracy and dynamic range of these optical devices are relatively general. As a solution, this paper presents the design of an electromagnetic feedback optical MEMS accelerometer with temperature control. Two single accelerometer chips form the acceleration sensing structure, assembled via manual micro-assembly. The electromagnetic feedback control system enables the sensor to operate in the linear range, and the temperature control system maintains a stable operating temperature for the equipment. The novel design of the sensing structure with two sets of control systems enables the accelerometer to have an extremely low noise floor, along with a wide dynamic range. Experimental results confirm that the device can achieve a voltage sensitivity of 2643 V/g and dynamic range values up to 3.9 mg. The self-noise of the sensor is less than 3 ng/√Hz in the frequency range from 0.8 to 7 Hz. The bias stability is 11.9 ng @ t = 1.8 s. Considering the excellent performance, the proposed device has significant application potential in seismic and gravity measurements.

A digital excitation-calibration technique of dual-mass MEMS gyroscope for closed-loop mode-matching control is presented in this paper. The technique, which takes advantage of the symmetrical amplitude response of MEMS gyroscope, exploits a two-side excitation signal to actuate the sense mode to obtain the corresponding DC tuning voltage. The structural characteristics of dual-mass decoupled MEMS gyroscope and the tuning principle of excitation-calibration technique are introduced firstly. Then, the scheme of digital excitation-calibration system for the real-time mode-matching control is presented. Simultaneously, open-loop analysis and closed-loop analysis are deduced, respectively, to analyze the sources of tuning error and system stability. To verify the validity of the scheme and theoretical analysis, the system model was established by SIMULINK. The simulation results are proved to be consistent with the theoretical analysis, verifying the feasibility of the digital excitation-calibration technique. The control algorithms of the system were implemented with a FPGA device. Experimental results demonstrate that digital excitation-calibration technique can realize mode-matching within 1 s. The prototype with real-time mode-matching control has a bias instability of 0.813 ${}^{\circ }$ /h and an ARW (Angular Random Walk) of 0.0117 ${}^{\circ }$ / $\sqrt{h}$ . Compared to the mode-mismatching condition, the bias instability and ARW are improved by 3.25 and 4.49 times respectively.

The design, analysis, and simulation of a new Micro-electromechanical System (MEMS) gyroscope based on differential tunneling magnetoresistance sensing are presented in this paper. The device is driven by electrostatic force, whereas the Coriolis displacements are transferred to intensity variations of magnetic fields, further detected by the Tunneling Magnetoresistance units. The magnetic fields are generated by a pair of two-layer planar multi-turn copper coils that are coated on the backs of the inner masses. Together with the dual-mass structure of proposed tuning fork gyroscope, a two-stage differential detection is formed, thereby enabling rejection of mechanical and magnetic common-mode errors concurrently. The overall conception is described followed by detailed analyses of proposed micro-gyroscope and rectangle coil. Subsequently, the FEM simulations are implemented to determine the mechanical and magnetic characteristics of the device separately. The results demonstrate that the micro-gyroscope has a mechanical sensitivity of 1.754 nm/°/s, and the micro-coil has a maximum sensitivity of 41.38 mOe/µm. When the detection height of Tunneling Magnetoresistance unit is set as 60 µm, the proposed device exhibits a voltage-angular velocity sensitivity of 0.131 mV/°/s with a noise floor of 7.713 × 10⁻⁶°/s/$\sqrt{\mathrm{Hz}}$ in the absence of any external amplification.