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A novel mode-localized acceleration sensor employing an electrostatically coupled resonator and integrating a lever with proof mass is micromachined using standard silicon on insulator (SOI) technology. In order to determine the linear dynamic range of the sensor, a reduced order model is developed while assuming that the resonators vibrate below the critical amplitude. Then, open-loop and closed-loop testing platforms are established to measure the performance of the linearly operating accelerometer in a vacuum environment (less than 5 Pa). Moreover, the corresponding amplifier circuit based on the capacitive detection principle is designed in order to extract and amplify the current signal from the resonators. The obtained results show that the accelerometer sensitivity can be increased by three orders of magnitude when using the relative shift of amplitude ratio as the output metric instead of the relative shift of frequency, and the experimental measurements are consistent with the theoretical predictions. Remarkably, the Allan standard deviation of the mode-localized acceleration sensor obtained from the closed-loop testing circuit is around 5.03 μg. [ABSTRACT FROM AUTHOR]

In order to explore the evolution law and mathematical characterization method of natural fissure structure of coal under uniaxial loading, a 3D numerical model was reconstructed based on computed tomography (CT) scanning experiment to accurately describe natural fissure structure, and the uniaxial compression numerical simulation of coal was carried out. The length, opening, fissure degree and fractal dimension were introduced to characterize the spatial morphology of fissure, and the variation of characterization parameters with increasing load was analyzed. The results reveal the evolution characteristics of fissure structure of coal under uniaxial loading. The study shows that the coal is mostly composed of small-scale fissure, and the fissure evolution can be divided into two stages during the loading process. In the first stage, namely the initial stage of loading, the fissure is compacted and closed. Compared with the non loading, the upper limit of fissure length decreases by -1-1%, the fissure degree decreases by 35%, and the fractal dimension decreases by 22%. In the second stage, fissure in the coal begin to develop with the increase of load. At peak load, the length increases by 10% on average, the distribution frequency of the minimum interval of fissure length increases by 12%, and the distribution frequency of the minimum interval of fissure opening increases by 50%. The research results provide a theoretical basis for revealing the laws of coal fissure propagation under loading and effectively implementing hydraulic fracturing technology. [ABSTRACT FROM AUTHOR]