High-Sensitivity Low-Cost 2.61 GHz DGS Sensor for Non-Invasive Glucose Level Monitoring

This work presents a loop-shaped (hairpin) resonator incorporating a defective ground structure (DGS) to enhance sensitivity for monitoring water–glucose solutions. The proposed sensor exhibits two resonant frequencies at 2.61 GHz and 4.07 GHz, with reflection coefficients of −46.60 dB and −23.00 dB, respectively. A set of measurements was conducted to compare the performance of the resonator with and without the DGS under two sample-placement configurations: one with water and water–glucose solutions positioned over the feed lines and metallic resonant elements, and another with the water–glucose solutions placed directly over the ground plane. Among the evaluated cases, the ground-plane configuration proved to be the most advantageous, as it produced no frequency shift while yielding distinct magnitude responses of −41.91 dB, −45.62 dB, −47.74 dB, and −49.69 dB for glucose concentrations of 100, 150, 200, and 250 mg/dL, respectively. Overall, the resonator with the defective ground structure consistently demonstrated higher sensitivity and a more stable response pattern, indicating its strong potential for glucose-level monitoring applications.