At the microscale, even moderate temperature differences can result in significant Knudsen forces generated by the non-equilibrium energy exchange between gas molecules and solids immersed in the gas. Exploiting the Knudsen force offers novel mechanisms for actuation, sensing, and energy harvesting in nano/microsystems. The gas Knudsen forces are significant in the presence of thermal gradients that are large on the scale of the gas molecular mean free path. Such conditions occur and can be created in a wide variety of applications involving micron-and submicron-sized structures and a gas ambient. The aligned computational and experimental efforts in this program will provide a pathway for analysis and control of thermal Knudsen forces in current systems "such as atomic force microscopy and MEMS structures" and for future high-precision thermal sensors and actuators.
Prediction of thermal Knudsen forces requires kinetic theory description of transport processes in the gas phase, which is beyond the capabilities of conventional macroscopic computational models. The basis for computational investigation is the deterministic solution of Boltzmann kinetic equations for coupled gas-solid thermal interaction in the subcontinuum regime. Closed-form models for Knudsen force will be developed based on the high-fidelity simulations for a wide range of conditions. The modeling will be validated by experimental measurements using Scanning Laser Doppler Vibrometry of microstructures with integrated nanoscale heaters under controlled ambient gas pressure and thermal conditions in a vacuum probe station. The experiments will provide direct calibrated measurements of Knudsen forces in geometries relevant for applications in practical engineered nano/microsystems.
The research results will be integrated into the courses on molecular gas dynamics and nano/microsystems engineering. An interactive online tool for simulation of Knudsen force effects in N/MEMS will be created and made available to a worldwide research and education community through nanoHUB (http://nanohub.org). This research is also combined with educational activities aimed at attracting and retaining minority students and providing research opportunities for undergraduate students early in their careers.
