Flexible Hot-film Anemometer Arrays for Flow Measurements on Curved Structures

摘要

In this paper, a set of flexible aeroMEMS sensor arrays for flow measurements in boundary layers is presented. The sensor principle of these anemometers is based on convective heat transfer from a hot-film into the fluid. All sensors consist of a nickel sensing element and copper tracks. The functional layers are attached either on a ready-made polyimide foil or on a spin-on polyimide layer. These variants are necessary to meet the varying requirements of measurements in different environments. Spin-on technology enables the use of very thin PI layers, being ideal for measurements in transient flows. It is a unique characteristic of the presented arrays that their total thickness can be scaled from 5 to 52 μm. This is essential, because the maximum sensor thickness has to be adapted to the various thicknesses of the boundary layers in different flow experiments. With these sensors we meet the special requirements of a wide range of fluid mechanics. For less critical flow conditions with much thicker boundary layers, thicker sensors might be sufficient and cheaper, so that ready-made foils are perfect for these applications. Since the presented sensors are flexible, they can be attached on curved aerodynamic structures without any geometric mismatches. The entire development, starting from theoretical investigations is described. Further, the micro-fabrication is explained, including all typical processes e.g. photolithography, sputtering and wet-etching. The wet-etching of the sensing element is described precisely, because the resulting final dimensions are critical for the functional characteristics.