The effects of air flow on the resonance properties of microcantilevers

The development of the atomic force microscope introduced the idea of using a microlength cantilever to detect a microsized phenomenon. It was found that a microlength cantilever could provide a useful optical or piezoresistive signal when it was bent or when its natural vibrations were altered. As research developed, the fluid medium surrounding the microcantilever became an influential parameter of experiments. As the fluid medium of microcantilevers was altered to create flow, the behavior of the microcantilevers was questioned and examined. In this experiment, measurements were made on the effect of air flow of various rates over microcantilevers in order to characterize some of the effects of flow. The complexity of flow was reduced by creating laminar parallel and perpendicular air flow over assorted microcantilevers (standard ShN4 triangular and rectangular microcantilevers and Si rectangular microcantilevers) in a range of common flow rates (approximately 0-80 ml/min). The effects of the flow were measured by obtaining the resonance frequency spectrum and deflection of the microcantilevers from an optical signal. As the flow rate increased, it was found that the resonance frequency increased, the quality factor decreased, the resonance amplitude increased, and static deflection occurred proportional to perpendicular velocity. The increases in resonance frequency and resonance amplitude were not expected, yet they do not contradict theory or existing research. They indicate more measurement possibilities in the realm of microcantilever research. The results obtained open the door to further work with different types of fluids where the properties of viscosity, density and fluid inertia could be further characterized and measured. High velocity airflow was examined in the hope that further signal amplification and velocity sensitivity could be obtained in the airfoil effect. No airfoil effect was measured, but the experimental conditions limited the flow velocity to below the speed of sound (which marks a change in functional dependence of the drag force to velocity-squared instead of velocity) and there were indications that turbulence may have occurred at the higher velocities. An attempt was made to utilize curved microcantilevers in the expectation that they would be sensitive enough to respond to the airfoil effect at lower velocities, but this did not work out. Further research with an improved cell is recommended to determine the potential for the airfoil effect to occur at a microscopic level, in order to obtain information for both microcantilever amplification and the understanding of fluids.