53 research outputs found
Investigation of Silicon Etching Effects for Monolithic Integration of MEMS with CMOS
Monolithic integration of CMOS and MEMS is quickly proving to be a viable asset to current complex structures. However, synthesis of these technologies has proven to have multiple processing obstacles. Depending on the method used to create these devices, the hurdles include the effects of silicon etching and high temperature processing. For this experiment, previously processed CMOS wafers were obtained and a trench was etched into the silicon. “Family of curves” plots of the working CMOS wafers were taken before and after processing to study any changes in ID. Results have shown that the processing of this integration will effect the family of curve plots, however this was not concluded as a result of a small sample size
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Drag Reduction In Turbulent Flows Over Micropatterned Superhydrophobic Surfaces
Periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide drag reduction in the laminar flow regime, have been demonstrated capable of reducing drag in the turbulent flow regime as well. Superhydrophobic surfaces contain micro or nanoscale hydrophobic features which can support a shear-free air-water interface between peaks in the surface topology. Particle image velocimetry and pressure drop measurements were used to observe significant slip velocities, shear stress, and pressure drop reductions corresponding to skin friction drag reductions approaching 50%. At a given Reynolds number, drag reduction was found to increase with increasing feature size and spacing, as in laminar flows. No observable drag reduction was noted in the laminar regime, consistent with previous experimental results and theoretical predictions for the channel geometry considered. In turbulent flow, viscous sublayer thickness appears to be the relevant length scale as it approaches the scale of the superhydrophobic microfeatures; performance was seen to increase with further reduction of the viscous sublayer. These results indicate superhydrophobic surfaces may provide a significant drag reducing mechanism for marine vessels
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Experimental studies of superhydrophobic surfaces in flow
In recent years, research on superhydrophobic surfaces has exploded from more than five decades of relative obscurity. The use of superhydrophobic surfaces in flow is but a small part of renewed interest in the field. Superhydrophobic surfaces which have previously demonstrated the ability to reduce laminar regime drag in certain flows, are shown to be effective in reducing drag in the turbulent flow regime as well. In some cases, skin friction drag reductions of 50% were observed. Drag reductions result from slip at the gas-liquid interface that exists at the surface. In a turbulent flow, this slip has a significant influence on the viscous sublayer nearest the wall, and drag reduction performance appears to scale with viscous sublayer thickness. On stationary cylinders superhydrophobic coatings reduce the intensity and increase the frequency of vortices shed behind the body. Separation point and the structures in the wake are visually altered in the presence of superhydrophobic slip, especially slip in the flow direction. On elastically mounted cylinders, slip reduces the amplitude of vortex induced oscillations, but not their frequency, indicating the result is primarily the result of reduced fluid forcing. Experiments with superhydrophobic coated hydrofoils demonstrated slip can reduce drag and lift over a range of attack angles. Engineered and randomly patterned superhydrophobic surfaces were shown to be effective in generating slip, although considerable care must be exercised with randomly patterned surfaces to ensure the appropriate slip lengths exist; an experiment to measure slip length is presented. Unlike the previous flow studies where slip is the responsible mechanism, studies of the effect of contact angle and density on the orientation and stability of floating cubes are concerned only with superhydrophobic surfaces\u27 high contact angles and resistance to wetting. These experiments show how the effect of high contact angles available from superhydrophobic surfaces can allow small objects, more dense than water, to float at the surface, a phenomenon observed with aquatic insects. A series of theoretical predictions are presented along with measurements of force and observations of floating cubes with known contact angles are presented. It is noted that cube size and contact angle determine the most stable orientation in which a cube of a given density will float, or if it will sink. Vertical edges and corners decreased the force and displacement a shape was able to bear before sinking, although the local shape and sharpness of the edge is likely to play a significant role
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