Scalable All-Printed Microwave Microfluidic Sensor for Multi-Liquid Characterization based on a Stub-Loaded Microstrip Line

Microwave microfluidic sensors are typically designed with a channel in vicinity of a resonator's fringing electric (E)-fields, to characterize the material properties of a single fluid. This paper leverages hybrid 3D and dispenser printing to realize a scalable microfluidic sensor utilizing the parallel-plate capacitance of an open-ended microstrip stub, enabling, for the first time, a tunable sensitivity. A stub-loaded microstrip line is then proposed for characterizing multiple microfluidic samples simultaneously using a simple two-port multi-band resonator. The physical constrains which limit the scalability of the proposed sensors have been analyzed analytically and numerically, prior to implementing a three-channel triple-band sensor. The microfluidic channels have been fabricated using stereolithography 3D printing with the microstrip line directly dispenser printed on a conformable polyimide substrate. To accommodate varying channel thicknesses, a tapered microstrip line is proposed to maintain the impedance matching. The fabricated sensor is characterized using binary water-IPA mixtures to evaluate its sensitivity, comparing favorably with reported 3D-printed sensors. The proposed sensor achieves over 90% accuracy in determining the real permittivity following a simple water-based calibration across the different channels, for samples with 16 oC temperature sensitivity across all channels.