Dielectric Characterization Using a High-Frequency Patch Resonator With Substrate-Integrated Microfluidic Channel

This paper introduces a single-port patch resonator with an embedded microfluidic channel for high-frequency dielectric characterization. The entire sensor is fabricated as a single unit through multi-material additive manufacturing, a process that ensures precise alignment between the sensor’s electromagnetic fields and the fluid sample for accurate, repeatable measurements. Two prototypes, resonating at approximately 12 GHz and 20 GHz, were printed on a low-loss UV-curable polymer substrate using silver-nanoparticle conductive ink. Experimental characterization involved water–ethanol mixtures spanning concentrations from 0% to 90% ethanol by volume, confirming clear, measurable shifts in resonance frequency as the permittivity of the fluid changed. A third-order polynomial model accurately related resonant frequency to sample permittivity, yielding coefficients of determination (R²) exceeding 0.999 for calibration datasets and above 0.974 for independent test samples. Additionally, root-mean-square measurement deviations remained consistently below 1.5% of the total observed frequency shift, reflecting high reproducibility. These findings establish that additively manufactured patch resonators are compact, reliable, and effective tools for label-free dielectric characterization, making them highly suitable for chemical and biomedical sensing applications.