Broadband Determination of Liquid Mixing Ratio through One-Port Microwave Measurements

This paper presents a method for determining binary mixing ratio of two liquids for microfluidic applications. The liquid mixtures are measured through sensor constituted by interdigital capacitor. Dielectric permittivity of the fluid is derived from the high-frequency capacitance measurements. Finally, the mixing ratio is calculated using frequency-dependent modified Bruggeman formula. The method is purely measurement-based and does not require electromagnetic simulations. The error for determining the mixing ratio is below 5% at frequencies above 1 GHz for water and isopropanol mixtures.