A miniature silicon hot wire sensor for automatic wind speed measurements

In order to make air flow measurements easier and more accurate, a very small sensor has been constructed. The fabrication of such a sensor mainly consists in depositing a thin doped polycrystalline silicon layer on a 4″ silicon wafer by using a silicon-micromachined technique. At the end of the integration process, the wafer is sliced into 46 wind sensors. Each of them comprises a polycrystalline silicon layer which is 0.5 μm thick, with width running from 2 to 5 μm and length, from 45 to 58 μm. Supplied with a dc electrical current, each layer acts as a hot wire on contact with the fluid under study. Wind speed is then measured by detecting the resistance variations caused by the thermal transfer from the heated layer to the ambient atmosphere. A microcontroller-based data acquisition system has especially been designed so as to collect the wind speed measurements arising from this kind of hot wire transducer. The integrated silicon sensors have been experimented within a wind tunnel and calibrated for air speed ranging from 0 to 35 m/s. Initially intended for wall shear stress monitoring, these sensors can usefully be employed as anemometers for wind energy applications.