A Fully Inkjet-Printed Flexible Microwave Multiresonator Circuit for Concentration Measurements of Liquid Solutions

A fully inkjet-printed flexible microwave multiresonator circuit is presented. It is based on a coplanar waveguide (CPW) coupled to three spiral resonators to create resonances in the frequency domain. The circuit is applied for the concentration measurements of binary liquid mixtures by characterizing the insertion loss response. Water/sodium-chloride concentrations (NaCl) in the range of [0, 100] μg/ml with an increment of 10 μg/ml per sample are measured in room temperature. Two parameters are used to quantify the sensitivity, the change of the insertion loss at the resonant frequency |ΔS₂₁|, and the shift of the resonant frequency |Δf_res| |ΔS₂₁| = 0.03 dB/(μg/ml) and |Δf_res| = 0.25 MHz/(μg/ml) have been achieved by the circuit within the concentration range of [0, 60] and [0, 100] μg/ml, respectively.