Research On Design Theory And Methodology Of Capacitive Inertial Sensors

Capacitive micro inertial sensors are typical components developed with MEMS technologies. They have extensive prospects in the fields of military equipments and industry products. But the performance of these sensors is very poor, and there isn't unified theory and methodology for them. Using capacitive micro accelerometers and capacitive micro gyroscopes as the research targets, this dissertation investigates the design theory and realization methods of micro inertial parts, focusing on structure design, modeling and simulation, detecting circuit and controlling means, structure optimization of sensors, and so on. Subsequent research contents and innovations are presented in this dissertation.1. Main objectives and contents of the design of micro accelerometers and micro gyros are brought forward. Comparing the shortcoming of conventional technique, new design way and flow are offered, fitting the characteristics of micro inertial sensors. Then their design procedure is specified. In addition, lumped parameter models are deduced for the complex supporting beams, air damp, sensing capacitor and electrostatic force driving structure. Equivalent inertial mass of those beams is detailedly computed using dynamics and mechanics of materials.2. According the designed single axis micro accelerometer, its modeling means is presented. The relations between its design parameters and its performance index are analyzed. Adopting the upper design methods, a novel all-differential triaxial accelerometer is formed. The conditions are provided to keep its sensitivities in all directions same. Cross disturbing problems are also clarified. All of these analyses offer a sufficient theoretical base to improve the detecting precision of the sensors.3. Tow kinds of electrostatic feedback cells are designed, and analog detecting and feedback control circuit models are set up. Design principles of circuits gain are concluded for improving the performance of sensors and restraining nonlinear problems. Besides, robust control methods are contrived to increase the stability of the closed system.4. A novel decoupled capacitive micro gyroscope is designed. Its driving mode and sensing mode employ the lateral comb array structure as the detecting capacitor and the longitudinal one as the driving capacitor. Based on its system model, all of its performance indexes are accounted.The relation between its sensitivity and resonance frequencies of the two modes are pointed out. Design rules of the sensitivity are provided. A new resonance frequency tuning method is put forward using the longitudinal comb. This affords a new way to enhance the gyro's sensitivity.5. Double closed control system model of the gyro is analyzed. According to characteristic of its structure and detecting signal, two novel control schemes are planed. One is to keep the resonance frequency invariable for driving mode. The other is to maintenance the same phase information between electrostatic feedback for and Coriolis force for sensing mode. It will effectively improve the dynamic characteristics of micro gyroscopes.6. Optimized design methodology for micro inertial sensors is concluded. Optimization designs are applied on the single axial microacceleoemeter, the triaxial one, and the decoupled micro gyroscope. Optimized parameters are computed using the theory. Circuit simulation is utilized to evaluate the micro inertial sensors. Besides, errors sources of micro capacitive inertial sensors are systematacially investigated. Error models are set up for machined defects and thermal noise of mechanical structures and control circuits.In this dissertation, most of technique difficulties of the design of capacitive micro inertial sensors are completely researched, and some effective countermeasures are put forward. The research conclusions are unique and the suggested methods are creative. Furthermore, all of them can be extended to guide the design of other kind of micro inertial sensors, micro actuators, micro pressure sensors and etc.