Differential Microfluidic Sensors based on Electroinductive-Wave (EIW) Transmission Lines

We show in this paper that electroinductive-wave (EIW) transmission lines can be applied to the implementation of differential-mode microfluidic sensors with high sensitivity. The sensor is based on EIW lines equipped with microfluidic channels for dielectric characterization of liquid samples. Deionized (DI) water is used as reference (REF) liquid, whereas solutions of isopropanol in DI water are used as liquid under test (LUT). In this sensor, the output variable is the cross-mode transmission coefficient, proportional to the differential transmission coefficient of both measurements, whereas the input variable is the differential permittivity (between the REF and LUT liquids), or any other variable related to it. Particularly, in this work the interest is the measurement of solute content in liquid solutions, used for validation purposes. The proposed sensors are highly sensitive by virtue of the high dispersion of EIW transmission lines.