Dynamic response of mini cantilever beams in viscous media

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Montana State University - Bozeman, College of Engineering


In concurrent engineering, viscosity and density of a fluid are two important parameters as they are the indicators of some predefined standards of the concerned fluids in some specified application. Arguably fluids play an important role in all major engineering applications starting from automobile to biofilm. In this work, we will demonstrate the use of mini cantilever beams for characterization of rheological properties of viscous materials such as lubricating oils. Further miniaturization of the test platform can lead to a MEMS device that can potentially be used for measuring the rheological properties of soft viscoelastic materials such as biofilm. Miniaturization of the measuring instrument is necessary so a small sample volume can be used to perform the test. In this study, the dynamic response of cantilever beams was measured experimentally in air and viscous fluids (e.g. water, and lube oils of three different grades) using a duel channel PolyTec scanning vibrometer. The changes in dynamic response of the beam such as resonant frequency, frequency amplitude, and the Q-factor were compared as functions of the rheological properties (density and viscosity) of fluid media. It may be mentioned here that we used two cantilever beam configurations, one was the plain small stainless steel beam and another was a small stainless steel beam with an aluminum mass attached to it. For both the configurations, the samples were excited by an external shaker at sweeping frequency modes and the beams' motions were recorded by the laser vibrometer focused at different locations of a beam's surface. The reflected signal is directed to a split photo detector whose output is sent to fast-Fourier Transform [FFT] spectrum analyzer.




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