Fabrication and Evaluation of a Flexible MEMS-Based Microthermal Flow Sensor

Abstract

Based on the results of computational fluid dynamics simulations, this study designed and fabricated a flexible thermal-type micro flow sensor comprising one microheater and two thermistors using a micro-electromechanical system (MEMS) process on a flexible polyimide film. The thermistors were connected to a Wheatstone bridge circuit, and the resistance difference between the thermistors resulting from the generation of a flow was converted into an output voltage signal using LabVIEW software. A mini tube flow test was conducted to demonstrate the sensor’s detection of fluid velocity in gas and liquid flows. A good correlation was found between the experimental results and the simulation data. However, the results for the gas and liquid flows differed in that for gas, the output voltage increased with the fluid’s velocity and decreased against the liquid’s flow velocity. This study’s MEMS-based flexible microthermal flow sensor achieved a resolution of 1.1 cm/s in a liquid flow and 0.64 cm/s in a gas flow, respectively, within a fluid flow velocity range of 0–40 cm/s. The sensor is suitable for many applications; however, with some adaptations to its electrical packaging, it will be particularly suitable for detecting biosignals in healthcare applications, including measuring respiration and body fluids.

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“…However, as the flow rate increases, the temperature difference corresponding to the resistance between the two thermistors decreases. As discussed in our previous study, the decrease in the average voltage amplitude with an increase in the flow rate is attributed to the difference in the temperature drop between the two thermistors. The upstream thermistor rapidly cools as the fluid passes through, resulting in minimal additional changes caused by the continuous flow rate, whereas the temperature of the downstream thermistor gradually decreases with increasing flow rate due to the heat supply from the microheater.…”

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“…7A). [57][58][59] Shear stress and flow rate can be measured by combining with simulation. 60 Ultra-thin glass is effective as well for sensitive sensing.…”