High-Accuracy Microwave Sensor for Glucose Detection Using a Slow-Wave CRLH Structure

This article presents the development of a microwave sensor designed to measure the permittivity of liquids using a novel slow-wave transmission line (SWTL) integrated with a composite right-left-hand (CRLH) element to achieve a Fano response and precise phase control. The incorporation of the SWTL significantly enhances the sensor's performance, leading to a higher Q-factor and improved sensitivity compared to a conventional sensor design. Notably, the Q-factor of the sensor's second resonance increases from 52.2 to 88.3 with the implementation of SWTL. The sensor demonstrates dual-band operation at 4.6 and 5.2 GHz, exhibiting a distinct Fano resonance. Moreover, the SWTL improves the electric field concentration in the interdigital capacitance, which acts as the unit cell's hot spot. The fabricated sensor measures the density of dissolved glucose in pure water, using polyamide tubes as loop-shaped holders filled with varying glucose concentrations. Sensitivity is evaluated based on both simulation and experimental results.