Hybrid Thermal and Mechanical 2D Anemometer Using Strain-Induced Out-of-Plane Cantilevers

An anemometer has been realized which combines thermal and mechanical measuring principles. It consists of four cantilevers that have bent out-of-plane after fabrication due to strain mismatched silicon-rich silicon nitride layers. Platinum wires on top of the cantilevers act both as Joule heating resistor and as strain gauges. The thermal hot-film and drag force sensing techniques are complementary: the thermal sensing element allows for accurate low-flow measurements down to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.2 \mathrm{m} \mathrm{s}^{-1}$</tex> while the mechanical sensing element allows for the measurement of higher flow rates up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$8.5 \mathrm{m} \mathrm{s}^{-1}$</tex> while maintaining high accuracy as a result of its linear response. Due to different orientations, the angle of attack of the flow is detected along the out-of-plan axis, allowing for wind direction determination.