Radiometric force as power source for microactuators

The use of micro-electromechanical systems (MEMS) has been growing rapidly in recent years and is further expected to play vital roles in an increasingly wide range of engineering designs in the near future. Electrostatic force has been the predominant means of powering MEMS actuators, but other alternatives are being explored for the improvement of performance and for meeting new needs in different application, as MEMS designs grow in sophistication and diversification. Radiometric force, consisting of thermal creep flow among others, is one such alternative and is a rarefied gas phenomenon that occurs in the presence of a temperature gradient. It is the same force that drives Crookes' radiometer, a well-known laboratory object. In a MEMS application, mechanical force arising from the thermally induced flow would be utilized to move the moving parts of an actuator, thereby driving it. The main advantage of thermal creep flow over electrostatic force is that it could eliminate the need of energy source inside an actuator and greatly simplify its design and improve its reliability. The feasibility of its use as the power source for MEMS actuators has been studied experimemally. A macro-scaled apparatus has been built to simulate a MEMS actuator and thermal creep flow has been induced to run it under varying, degrees of gas rarefication and applied temperature gradients. The design of the apparatus and its concept are presented. The Direct Simulation Monte Carlo (DSMC) method has been compared to the experimental results and to test additional design criteria. The performance of the present apparatus and that of a similar actuator studied with DSMC in the past have been compared and is discussed.