Microfluidic-microstructure interaction study under oscillating flows : design, modeling, testing and verifications

In microsystem applications, many MEMS devices are submerged in fluid and their responses and performances are directly influenced by the microfluid-microstructure interactions. Recent developments in microfluidic devices such as micro pumps, micro valves, micro viscometer, biomedical related micro fluidic chips, have necessitated investigations on fluid-structure interactions at the micro levels. A microcantilever submerged in microfluidic channel forms the simplest model for such investigations. The study of such interactions however necessitates systematic developments in suitable experimental methods. In this dissertation, a polymer base micro-fabrication process called "soft-lithography" is adopted to fabricate microcantilever integrated microfluidic channels. An experimental setup is designed to characterize the dynamic behavior of the submerged microcantilever using a new method called DVIP (Deflection using Video Image Processing) method. The DVIP method is used to estimate the deflection or dynamic responses of microcantilever under different flow conditions. The flow behaviors could also be characterized from the response of the microcantilever. A finite element model of the microstructure is developed and results obtained from this model are validated using the experimental results. The finite element model also provides considerable potential to investigate the influence of fluid viscosity on the dynamic responses of the microcantilever. A microcantilever integrated within the microfluidic chip was subsequently tested in the laboratory with fluids of different viscosities. The results obtained are analyzed and discussed in the context of an application development such as a viscometer. An effort is made to visualize the flows near the cantilever tip using the fluids mixed with fluorescent particles. The DVIP method is further extended to estimate the full cantilever beam deflection, which can be applied for determining the mode of vibration. Finally, it is established that the DVIP method is a reliable approach to estimate the dynamic deflections of a microcantilever subject to fluid forces. The concept of the micro viscometer that is developed in the current study can be miniaturized by integrating a miniature camera and an integrated circuit within the microfluidic chip. The current study, however, is limited to square cross-section microfluidic chip, while the proposed methodology would be applicable to study the responses of the microcantilever integrated within channels of different cross-sections. The DVIP method also offers considerable potential to characterize nano-electromechanical devices by integrating a more efficient and faster camer