Lubrication theory has been one of the most successful and widely used theories in all of engineering and applied science. However, in a wide range of conditions applicable to many researchers in microelectromechanical systems (MEMS), experimental results seem to indicate that forces separating squeezing surfaces vary according to film thickness to the power minus one, rather than minus three, as lubrication theory requires. Hydrodynamic forces arise incidentally, and are usually the largest source of parasitic losses. The motivation of this research is thus to resolve the contradiction between experimental results and theoretical predictions concerning squeeze film dampers. The objective is to develop an improved theory of hydrodynamic lubrication at the microscale. These goals have important implications in the design of MEMS devices. A combined experimental and theoretical/modeling approach will be followed. The damping coefficient will be directly determined as opposed to indirect measurements in the existing MEMS experiments. A theoretical framework for corrections or modifications to lubrication theory will be proposed and tested both by experimental and numerical studies.
Employing active MEMS for actuation and sensing in a liquid environment has potential applications in many technologies of industry and medicine. However, the current lack of understanding of lubrication in microscale systems hinders the development of liquid immersed MEMS. There is a real need for developing trusted accurate verified models liquid damping in microscale systems in order to design reliable devices, able to perform as expected. In addition, the PI and co-PI will outreach to K-12 students by building a portable macro scale squeeze film test rig, as dynamically similar to the microscale research device as possible. Bringing theory to life, K-12 students can perform simple experiments and compare their measured effects to the microscale, by visiting the lab, or by web interaction with laboratory results.
The evaluation of fluid damping, or energy loss, is crucial to the design of microsystem (MEMS) devices. In a MEMS device, such as a torsional mirror, the sensing or activating element plate undergoes squeezing motion normal to a fixed substrate (and possible sliding) with respect to a nearby surface, generating hydrodynamic lubrication-like forces. In the design process, complex dynamic MEMS structures must be modeled. Generally, these hydrodynamic forces are not used to lubricate or separate surfaces, but arise incidentally. However, they often comprise the largest applied forces to the system, and the largest source of parasitic losses. Useful, trusted, and verified formulas for damping are not available to those who model dynamic MEMS systems. Our project goal is to develop and experimentally verify such a model. We have devolped such a comprehensive model including fluid viscous and inertia forces. The latter is not included in the conventional classical theory and may be of primary importance. We also allow for small and large oscillation apmplitudes. Again, the latter (being nonlinear) is not included in many existing approaches. We have perfomed experiments to validation the model, which also require accounting for a tilt angle between the plate and substrate. The correlation between the model and experiment is satisfactory.
