A compact and sensitive spurline-based microwave sensor for non-invasive glucose detection

Non-invasive blood glucose monitoring remains a critical need in diabetes management, prompting the development of compact, sensitive, and user-friendly sensing technologies. This study presents the design, fabrication, and experimental validation of a compact microstrip spurline-based microwave sensor tailored for non-invasive glucose detection. Leveraging low-cost FR4 PCB technology and a multi-spurline-based resonant sections, the proposed sensor operates efficiently within the 1.5–4 GHz frequency range. A cylindrical sample chamber enables precise characterization of glucose solutions with concentrations spanning 0.5–4 g/dL. Both simulated and measured results confirm the sensor’s high sensitivity to changes in relative permittivity, with a pronounced correlation between glucose concentration and resonance frequency (Fr) as well as reflection coefficient (S11). A dual-parameter sensing strategy is adopted, supported by mathematical models that capture the nonlinear dependence of |S11| and Fr on dielectric variations induced by glucose levels. Experimental data reveal a peak sensitivity of 20 × 10⁻³ dB/(mg/dL) in amplitude and 121.82 kHz/(mg/dL) in frequency, demonstrating superior performance compared to state-of-the-art counterparts in terms of resolution, response time, and sample volume (50 µL). The sensor’s miniaturized footprint, ease of fabrication, and robust electromagnetic response position it as a viable solution for real-time, low-cost, and non-invasive blood glucose monitoring, with significant implications for wearable and point-of-care diabetic diagnostics.