Modeling and Characterizing an Impedance-Type Micro Flow Sensor With Pulse Excitation

Abstract

This letter presents the modeling and characterization of a pulse-excited micro thermal flow sensor based on electrochemical impedance sensing. The proposed transient model reveals that the sensor output, measured as the impedance slope under pulse excitation, is almost one order of magnitude stronger at the downstream electrodes, as compared to the upstream pair. Consequently, the micro-electromechanical systems (MEMS) flow sensor is designed with an 8-μm-thick flexible structure and a 1.4 mm distance between the microheater and downstream electrodes. Testing results show that the fabricated impedance-type micro flow sensor achieves a maximum sensitivity of 8.9 (mΩ/s)/(μm/s) for the 1X PBS flow, while consuming less than 15.8 mW of heating power with a fluid flow up to 750 μm/s. Furthermore, the proposed theoretical model closely aligns with experimental results, confirming its potential as a valuable tool for optimizing impedance-type flow sensors that utilize pulse heating strategies to detect extremely low fluid flow in the future.