Design And Characteristic Study Of Three Dimensional Capacitive Acceleration Sensor

With the advantages of high sensitivity, low temperature coefficient, low power consumption and low cost, etc., MEMS capacitive accelerometer have been widely used in automotive, industrial, consumer electronics, oil exploration, navigation and other fields, and it should have a very broad market prospects and research potential.First this paper comparatively analyses the influnces of different detection structures on MEMS capacitive sensors properties. Studies show that the grid capacitance structure has the maximum quality, minimum air damping force, smaller mechanical noise, and the capacitance sensitivity is relatively large; the comb capacitance structure has smaller quality, but the larger mechanical noise and smaller capacitance sensitivity; then the comb-grid capacitance structure is in characteristics between other two structures, and it is suitable for making the sensor which has the middling sensitivity and resolution.Then, an accelerometor with the actuators drived by Lorentz force for increasing the initial sensing capacitance according to analysis above is designed. Using the finite element software ANSYS, the sport mode, the static sensitivity and impact resistance of the sensor designed are simulated and analysed. Results show that the stiffness of support beam is large in non-sensitive direction, and lower sensitivity of the acceleration signal, which greatly inhibits the axial cross-effect. The sensitivity of the sensor in the sensitive direction Y axis is 0.6478μm/g, and the accelerometor can sustain 1000g acceleration.The models of the open-loop and closed-loop system are built using Matlab/Simulink. After analyzing the influces of plate distance, fringe effects, and air damping on response, the reasonable working spacing can be confirmed. Studies show that the effect of the spacing on the displacement response can be neglected and the mechanical noise is greatly reduced after etching damping slots. The fringe effect has considerable influence on the sensor's static initial capacitance, and the influence on the sensor which is etched damping slots is greater than that pre-etching. Using this method, we can also choose other appropriate parameters of the sensor to the purpose of optimize the performance. Then the simulations of both open-loop and closed-loop models are finished. Results show that the sensor can maintain linearity within-10g～10g after adding the PID regulator, while the linear measure range is only-2g～2g in open-loop state. The resonant frequency in closed-loop state is 1173 Hz, which is almost as twice as that in open-loop state, and the bandwidth frequency is also up to 2865 Hz. The stability of the closed-loop real-time system has been greatly enhanced and the response time is only 3 ms. Then the manufacturing processes of the accelerometer are designed, and the designed accelerometer was manufactured which proves the feasibility of the designed process and the preliminary static test was issued, which indicates the feasibility of increasing the initial sensing capacitance with the actuators drived by Lorentz force. To deal with the installing error of three-dimensional combination the paper describes the compensation method based on optical alignment, and an example is showed to demonstrate the feasibility of the method.Finally, the interface detection circuit of accelerometer is proposed. Then the simulation of the designed circuit is finished using software Multisim10.0 and the simulating results are analyzed. At last the circuit experiment is finished.