Microscale In-Plane Knudsen Radiometric Actuator: Design, Characterization, and Performance Modeling

Thermally driven gas flow is exploited in a microscale device for the purpose of gas pressure dependent actuation in rarefied environments. The device relies on the in-plane motion of a shuttle mass in response to Knudsen thermal forces. The shuttle response is measured capacitively and the magnitude is used to estimate ambient pressure. Combined with heating element resistance, these measurements, in principle, enable the simultaneous determination of gas composition if the constituents are known. Numerical simulations using direct simulation Monte Carlo are carried out to elucidate the mechanisms of force production. Results reveal highly vortical flow structures forming high pressure regions at the shuttle surface. The experimental and numerical results are expressed in terms of a non-dimensional Knudsen force coefficient, allowing force magnitude to be estimated for dynamically similar geometries.