Design Of Resonant Micro-accelerometer Based On Electrostatic Stiffness Sensitivity Principl

With the rapid development of China’s economic and social construction,the demand for micro-accelerometers has soared unprecedentedly.Among them,resonant microaccelerometers have advantages of high sensitivity,low noise,and low power consumption.Therefore,resonant micro-accelerometers are widely used in precision mechanical machine tools,high-precision inertial navigation fields,et al.The resonant micro-accelerometer based on electrostatic stiffness can adjust the electrostatic negative stiffness by changing the detection voltage,thereby changing the sensitivity of the micro-accelerometer.And it can effectively overcome the existing problems of the resonant micro-accelerometer based on axial and lever forces currently being developed in China: low sensitivity,mechanical coupling,processing errors,and other issues.Therefore,the resonant micro-accelerometer based on electrostatic stiffness is expected to become one of the key development directions of high-precision microaccelerometers.In this paper,the finite element simulation is firstly carried out around the vibration beam stiffness constraints of the relationship between the sensitivity and the detection voltage in the resonant micro-accelerometer based on electrostatic stiffness,the working mode shape is determined,and the structural design of the micro-accelerometer meets the constraint of vibrating beam stiffness.Then the open-loop test was carried out after the packaging of the micro-accelerometer was completed,and it was found that the increase of the detection voltage would cause the amplitude and frequency coupling of the resonant beam.Therefore,a PLL+AGC double-loop closed-loop control circuit is designed,and three kinds of Allan variance analysis methods are used to analyze the stability of the output signal.Finally,a highprecision frequency measurement interface circuit based on FPGA is designed to collect the output frequency signal.The open-loop test shows that the resonant frequency of the micro-accelerometer is35.2986 k Hz when the acceleration is 0 g and the detection voltage is 1 V,and the quality factor is about 1076.The closed-loop test shows that when the detection voltage is 1 V and 2 V in the range of-1 g-1 g,the sensitivities are 44.5 Hz/g and 321 Hz/g respectively,which verifies the adjustable sensitivity of the micro-accelerometer;the internal frequency stability is ±10 ppm,the amplitude stability is ±30 ppm,and the micro-accelerometer resolution is 56 μg under constant temperature conditions.The absolute frequency error of the frequency measurement circuit is less than 0.1 m Hz,and the accelerometer can achieve a resolution of 124 μg when the frequency drift is not constrained.