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Towards a robust thin film sensor for distinguishing fluids using the 3ω-method

: Bernhardsgrütter, Ralf E.; Hepp, Christoph J.; Schmitt, Katrin; Jägle, Martin; Pernau, Hans-Fridtjof; Wöllenstein, Jürgen


Sensors and Actuators. A 321 (2021), Art. 112419
ISSN: 0924-4247
Fraunhofer IPM ()
3-Omega-Method; Thermal System; thermal conductivity; Multilayer System; In-line Measurement

This article presents a platinum thin-film sensor to distinguish fluids via their thermal properties by applying the 3-Omega-method. The thin film element is attached to a stainless steel tube piping the fluid. The fluids of interest in this article are gas (air), water, and alcohol (isopropanol). The progress claims include: First, the 3-Omega-method is applied to distinguish fluids which are not directly in contact with the sensitive structure. Second, the 3-Omega-method is applied on a meander structure instead of the commonly used straight strip. These two features should lead to high flexibility, high corrosion resistance and high hygiene and safety standards in applications. Third, because of the complexity of the sensor structure, a simplified analytical model is elaborated and a numerical simulation is conducted to obtain a profound understanding of the sensor's behavior. Based on these results, the sensor is designed and manufactured by standard thin film technology. The agreement between experiment and simulation results is within 5%. These findings can play a key role for future in-line sensors in process control systems e.g. in the food industry. Moreover, a deep understanding of the sensor's physical behavior with respect to its thermal properties can lead to a feasible combination of the 3-Omega method and thermal anemometry to achieve a robust thermal flow sensor, which is able to compensate the dependence on the thermal properties of different fluids.