Micro Thermal Flow Sensor for Ion Solution Based on the Monitoring of Slope of Impedance Changes

In this paper, a flexible and cost-effective micro thermal flow sensor based on the slope monitoring of electrochemical impedance changes is proposed for ion solution. Unlike the thermal flow sensors with thermo-resistive or thermoelectric transduction principles, the proposed flow sensor uses the electrochemical impedance of ion solution as a thermistor to sense the temperature change aroused by the fluid flow. Based on this mechanism, the detection range of the fabricated micro flow sensor implemented on the PI substrate is from 0 μm/s to 1000 μm/s, and the overheating temperature is lower than 5 °C. Besides, a one-dimensional (1-D) transient theoretical model is proposed, which is in good agreement with the experimental data. This model will be used to optimize the impedance-based flow sensor performance with very low detection limits for ion solution in the future.