Capacitive displacement transducers (CDTs) have been widely used in many physical sensors, attributing to high-resolution, simple electricity and easy manufacturing process. Gap-variation CDTs generally have higher displacement resolution due to small electrode gaps but suffer from the pull-in effect, the nonlinear effect and squeeze-film damping; whereas area-variation CDTs have intrinsically good linearity and much smaller slide-film damping. However, the parallel-plate-based area-variation CDTs have the electrode width much larger than the electrode gap with negligible fringe effect; therefore, the sensitivity is limited by periodic electrode numbers. In this paper, we introduce a novel fringe-effect dominated areavariation CDT with a much higher sensitivity within a certain electrode-deployable area. Both theoretical and numerical analysis are applied to investigate the working principle of the CDT design. The proposed fringeeffect-based CDT benefits from a much larger capacitance-to-displacement sensitivity than the traditional periodic array parallel-plate-based CDT, due to the more displacement-sensitive fringe field and more deployable electrode periods. A set of experiments are designed, and the proposed area-variation CDTs are evaluated. Experimental results suggested that the proposed CDT design, which had equal electrode width, separation and gap, could universally be applied to sensors with different featured dimensions either in macroscale or microscale. Angular misalignments with both out-of-plane tilts and in-plane rotations, which affect the output offset and sensitivity, should be minimized or alleviated. The proposed fringe-effect-based CDT are successfully applied to a single-axis in-plane sensing micro-electromechanical systems (MEMS) accelerometer, showing a noise floor as low as 0.25 ng/Hz 1/2 @1 Hz. The corresponding displacement noise of the proposed CDT is 0.1 pm/Hz 1/2 .

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Most spaceborne scientific experiment applications require a microgravity environment. The current high-precision accelerometers used for the spaceborne vibration isolation system generally have a noise floor of sub-μg/√Hz, which cannot meet the demand of higher-level microgravity measurements. This article introduces a micro-electromechanical system (MEMS) acceleration sensor that has a noise floor of 2–5 ng/√Hz and an input range of more than ±2 mg. Its three-component version, the MEMS microgravity measurement module (MEMS-M3), is designed to measure accelerations in the space microgravity environment and might be used in the active vibration isolation system for higher-level microgravity scientific experiments in the future. The MEMS-M3 has a volume of 105 × 90 × 115 mm3, a weight of 1.2 kg, and power consumption of 3 W. The performance of the MEMS-M3 has been characterized on the ground and a series of preflight reliability experiments have been conducted. Then, the MEMS-M3 installed inside the test spacecraft has been carried by the Long March 5B rocket (CZ-5B) to the low Earth orbit at 10:00 on May 5, 2020, and returned to Earth ground at 5:00 on May 8, 2020, both in UTC time. During the on-orbit period, the MEMS-M3 has been switched on for 11 h. After data processing, the transient, periodic, and steady accelerations can be observed by the MEMS-M3 and a much noisier shelf product IMU STIM300, verifying the functionality of the MEMS-M3. Apart from application in active vibration isolation systems for spaceborne scientific experiments, it can also be used for drag-free control of satellites and other space applications.

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