Comprehensive Model for Thermopneumatic Actuators and Microvalves

Thermopneumatic actuators have been used in a variety of microelectromechanical systems (MEMS) applications, particularly in the area of microvalves. However, a relatively simple model which relates the steady-state and transient response of the actuator to all important structural and boundary conditions has been lacking. In this work, a comprehensive model for thermopneumatic actuation is presented. The full thermodynamic nature of the thermopneumatic control fluid is modeled, including the change of phase from liquid, to liquid-vapor, to vapor, and back again. The thermodynamic model is coupled thermally and mechanically to a silicon membrane microstructure. The steady-state and transient response of the full actuator is modeled successfully, as represented by the application of the model to several modalities of interest. These include steady-state, isothermal flow of a compressible gas in a normally closed microvalve, and transient, nonisothermal flow in a normally open microvalve. This paper finishes with a discussion of the relevant assumptions in the model, the validity of the assumptions, and how departures from these assumptions can be assessed