The Modeling And Simulation Of Variable-Area Differential Capacitive Accelerometer

Silicon capacitive accelerometer is an example of the most rapidly and successfully development in the field of MEMS (Micro Electro Mechanical System) .MEMS is notjust the miniaturization of the traditional machines, new analysis and design methods need to be developed to meet the further development because of the size and surface effects encountered in micro systems.The modeling and simulation of MEMS then play an important role in this field because these techniques are very important for improving its performance, shortening its development period and lowing its cost. The capacitive accelerometer is one of the typical MEMS products.The research on its modeling,simulation and optimization is of great referential value for exploring the technolo- gy of the modeling and simulation MEMS.This theis first states the category,background and present situation,then introduce several typical micromachined capacitive accelerometer designed in recent years and analyze them in detail respectively.Based on the operating and mechanical principle of capacitive accelerometer,we designed a kind of Variable-area differential capacitive accelerometer with folding rectangle-spring beam. The structure of its sensitive element is composed by Spring-Mass-Spring, belong to the second-order vibration system. Further, the formula of mass displacement under accelerometer, variation of capacitance and the effective rigidity of folding spring are deduced by utilizing knowledge of material mechanics. From these formula, we get the relationship among structural parameters. In addition,this theis study the effective operating range of folding spring through its analysis of inactivation. The performance index such as natural frequency, sensitivity, measurement range damping,distinguishability are also discussed. Furthermore,the method of theory optimization is put forward,acted as a theoretical basis for the modeling and simulation.Applied with ANSYS, a software of finite element,we designed double spring and four spring structure,their first four modals of micro structure are obtained through changing the size of spring and mass. Besides displacement and modal of mass, we also studied the distribution of stress on folding spring. After the analysis of statics and transient dynamics and compared the results of two structure, we decided to adopt four folding spring structure. Further, we also got the optimally size of sensitive chip.