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