Precise measurement of variations in the local gravitational acceleration is valuable for natural hazard forecasting, prospecting, and geophysical studies. Common issues of the present gravimetry technologies include their high cost, high mass, and large volume, which can potentially be solved by micro-electromechanical-system (MEMS) technology. However, the reported MEMS gravimeter does not have a high sensitivity and a large dynamic range comparable with those of the present commercial gravimeters, lowering its practicability and ruling out worldwide deployment. In this paper, we introduce a more practical MEMS gravimeter that has a higher sensitivity of 8 μGal/√Hz and a larger dynamic range of 8000 mGal by using an advanced suspension design and a customized optical displacement transducer. The proposed MEMS gravimeter has performed the co-site earth tides measurement with a commercial superconducting gravimeter GWR iGrav with the results showing a correlation coefficient of 0.91.

High-precision microelectromechanical inertial sensors based on spring-mass structures are of great interests for a wide range of applications, including inertial navigation, disaster warning and resource exploration. Lowering the resonant frequency is essential to further improve the sensitivity of the sensors. However, conventional approaches are facing insurmountable difficulties from size reduction to machining precision. This paper proposed a novel quasi-zero-stiffness mechanism that is compatible with MEMS technologies together with a micromaching approach for adjusting the stiffness precisely. By improving the compliance of a typical spring with a negative-stiffness compensation mechanism induced by axial force, the resonant frequency of the micro spring-mass structure is lowered to 0.7 Hz, which is at least 3 times lower than current state-of-the-art micro structures. Based on this ultra-sensitive micro structure base on the quasi-zero-stiffness mechanism, the micro inertial sensor, with a chip size of a postage stamp, has shown a low self-noise of 0.6 nrad/√ Hz at 0.04 Hz and a high long-term stability that are comparable to traditional pendulum inertial sensors. It is the first micro device, to our knowledge, that can successfully measure the tidal tilt signal. [2020-0048]

We report an isoelectronic test of non-Newtonian forces at micrometer range by sensing the lateral force between a gold sphere and a density modulation source mass using a soft cantilever. Two-dimensional (2D) force mapping, in combination with in situ topographic imaging, is applied to verify the isoelectronic property of the surface. The force signal is found to be electrostatic force dominated, which is correlated with the density modulation structure for thinner gold coating and reduced by thicker gold coating and thermal annealing. Maximum likelihood estimation is used to extract the constraint on the hypothetical force based on the 2D data, and the experiment sets a constraint on the Yukawa type forces without subtraction of the model dependent force background. This result would be a meaningful complementary to previous tests with different methods.

Encoder-like micro area-changed capacitive transducers are advantageous in terms of their better linearity and larger dynamic range compared to gap-changed capacitive transducers. Such transducers have been widely applied in rectilinear and rotational position sensors, lab-on-a-chip applications and bio-sensors. However, a complete model accounting for both the parasitic capacitance and fringe effect in area-changed capacitive transducers has not yet been developed. This paper presents a complete model for this type of transducer applied to a high-resolution micro accelerometer that was verified by both simulations and experiments. A novel optimization method involving the insertion of photosensitive polyimide was used to reduce the parasitic capacitance, and the capacitor spacing was decreased to overcome the fringe effect. The sensitivity of the optimized transducer was approximately 46 pF/mm, which was nearly 40 times higher than that of our previous transducer. The displacement detection resolution was measured as 50 pm/√Hz at 0.1 Hz using a precise capacitance detection circuit. Then, the transducer was applied to a sandwich in-plane micro accelerometer, and the measured level of the accelerometer was approximately 30 ng/√Hz at 1Hz. The earthquake that occurred in Taiwan was also detected during a continuous gravity measurement.