Slot-Enhanced Dual-Band Microstrip Ring Resonator Sensor for Non-Invasive Blood Glucose Measurement

Abstract

This paper presents a new solt-enhanced dual-band microstrip ring resonator for non-invasive glucose estimation fabricated on FR-4. The slot placed beneath the sample to increase electric-field participation in the sensing volume. The structure supports two well-separated resonances near 2.4 GHz and 5 GHz whose minima shift monotonically with glucose con centration across 0–400 mg/dL, enabling linear inverse modeling and ratio metric features that mitigate common-mode drift. Five regression models were evaluated—single-band linear and quadratic (for each band) and a dual-band linear mapping using (f1,f2)—on a dataset generated with a Debye-based permittivity parameterization; the dual-band linear model delivered the best accuracy–robustness trade-off with training MAE = 8.53 mg/dL, RMSE = 10.13 mg/dL, R2=0.9938, and leave-one-out cross validation R2=0.9881, MAE = 12.23 mg/dL, RMSE = 14.11 mg/dL, whereas a quadratic dual-band alternative over fit. Frequency-detection resolution and normalized sensitivity are reported for both bands to support fair comparison among configurations, and the slot-enhanced layout achieves higher sensitivity without sacrificing compactness, indicating a practical path toward calibration-efficient bio sensing

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