Dynamic Modeling and Design of a High Frequency Micro Vacuum Pump

A dynamic model of MEMS-fabricated multistage micro vacuum pumps for use in a highly-integrated chemical monitoring system is described. A thermodynamic analysis shows that in order to meet the performance requirements of the system, the micro pump must be operated at very high frequency of approximately 50 kHz. At these frequencies, dynamic effects and resonances due to the interaction of the valves and the pump cavities can play an important limiting role in pump performance. Dynamical effects can also increase the pressure difference between pump cavities increasing the required actuation voltage. The present dynamic model uses integral forms of the momentum and mass conservation equations. Key components of the model are the viscous and inertial terms of the pump’s “checkerboard” microvalves, which are evaluated using a CFD model of the valves. At low frequencies, the model results show increased mass flow rate with increased frequency in good agreement with a thermodynamic model. Maximum performance is reached at frequencies of the order of the resonant frequency of the micro pump. The model is also used to study the effect of valve timing and operating point on mass flow rate and power consumption at high frequency.