Low-cost inkjet-printed t-type coplanar waveguide sensor for high-dielectric liquid sensing applications

Abstract This paper presents a T-type contact coplanar waveguide (CPW) radio frequency (RF) sensor designed for the detection of liquids with high dielectric constants, ranging from 63 to 104. The resonant frequency of the CPW structure is highly sensitive to both its geometric configuration and the dielectric properties of the surrounding medium, making it particularly suitable for liquid sensing applications. Using high-frequency electromagnetic simulations, the sensor was first optimized for a specific water sample and subsequently adapted for a broader range of high-dielectric liquids. The resulting resonance frequency shift among different liquid samples ranged from a minimum of 10 MHz to a maximum of 280 MHz, demonstrating significant sensitivity. To validate the simulation results, the sensor was fabricated using a direct deposition technique, employing silver nanoparticles (AgNPs)-based ink printed onto a transparent polyethylene terephthalate substrate. This fabrication approach enables low-cost, scalable, and environmentally friendly production. Surface characterization confirmed uniform and smooth deposition of the conductive AgNP layer with ~ 450 nm thickness. Experimental testing further verified that the resonance frequency shifted predictably in response to each tested liquid, aligning closely with the simulated outcomes. This work demonstrates that the proposed T-type CPW RF sensor is a promising for liquid detection, offering potential applications in areas such as quality control, process monitoring, and biomedical diagnostics. The integration of simulation-driven design and additive manufacturing indicates the feasibility of deploying such sensors in real-world scenarios.