Microwave Resonator-based Microfluidic Sensors Fabricated Using 3D-Printing Technology

Microwave resonators can be utilized as precision, fast, selective, and non-invasive sensors for reagent and material characterisation. The quality factor (Q-factor) of a microwave resonator determines its dielectric sensing performance, and the value of Q-factor can be improved by the resonator structure optimisation. However, conventional microwave resonator fabrication can be a complex, time-consuming process that constrains the device prototyping and development. Here we present a low-cost, fused filament 3D printing method to effectively fabricate integrated, split-ring microwave resonators with fluidic inducts, operating in the frequency range 2 to 4 GHz. Finite element modelling is employed to simulate the microwave resonation of sensing aqueous droplets in continuous mineral oil flow, using COMSOL Multiphysics software. We evaluate the sensing performance of different 3D-printed microwave resonators with geometrical variations of ring shapes, sizes, and numbers of split gaps, focusing on the increase of their Q-factors for improved sensitivity. Our work demonstrates a rapid prototyping approach to optimise microwave resonator, that can be applied to flow chemistry and engineering biology applications for functional soft material development purposes.