A Bidirectional Hot-Film Anemometer Based on Micromachined aGe Thermistor Technology
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The 13th Mechatronics Forum International Conference Proceedings
We report on simulation-based sensor design and measurement results of a bidirectional micromachined hot-film anemometer. The device is based on a thin-film thermistor made of amorphous germanium embedded in a silicon nitride membrane. The germanium structure is divided by metal-strip electrodes into four equivalent thermistor segments which are connected to form a Wheatstone bridge. The sensor combines hot-film and calorimetric transduction principles. The flow dependent cooling of the hot-film results in a unipolar, strictly
monotonic transduction characteristic which is utilized for flow velocity measurements. Moreover, convective heat transfer
between the hot-film segments causes thermal asymmetry
yielding a bridge detuning voltage with a bipolar characteristic where its sign corresponds to the flow direction. Consequently, the sensor features a strictly monotonic transduction characteristic over a wide flow velocity range combined with simultaneous detection of the flow direction. The device was characterized in both CCA and CTA operating modes.