Uncovering the Contribution of Microchannel Deformation to Impedance-based Flow Rate Measurements
Pengfei Niu, Brian J. Nablo, Kiran Bhadriraju, Darwin R. Reyes-Hernandez
Here we describe the exact processes occurring between two metallic electrodes when measuring volumetric flow rate by electrical impedance in polydimethylsiloxane (PDMS) microchannel. A considerable fraction of the change in impedance, due to change of flow rate, is caused by the variation of bulk solution resistance, rather than the disruption of the electrode/electrolyte interface which was considered as the main cause. The variation in solution resistance is due to the channel deformation under pressure. Placing electrodes near the microchannel inlet produces higher sensitivity due to greater channel deformation than those downstream. The critical factors that influence the sensors sensitivity are those that can change the bulk solution resistance, such as diluting solution concentration and widening electrode distance. This finding is of paramount importance for designing impedance based flow sensors.