# A Linear and High-Sensitivity Microwave Biosensor on a FR-4 Substrate for Aqueous Glucose Monitoring Using a Concentric Square-Shaped Split-Ring Resonator

## TL;DR

A new microwave biosensor is developed for non-invasive glucose monitoring with high sensitivity and accuracy.

## Contribution

A compact, dual-band biosensor using a concentric square-shaped split-ring resonator on FR-4 for linear glucose detection.

## Key findings

- The biosensor shows linear and monotonic response up to 250 mg/dL glucose with high R2 values.
- It achieves frequency and amplitude sensitivities of 1.964 MHz/(mg/dL) and 0.0332 dB/(mg/dL), respectively.

## Abstract

Non-invasive glucose monitoring remains a significant challenge in diabetes management, with existing approaches often limited by poor accuracy, high cost, or patient discomfort. Microwave-based biosensors offer a promising label-free alternative by exploiting the dielectric contrast between glucose and water. This paper presents a compact, dual-band concentric square-shaped split-ring resonator (SRR-type) biosensor fabricated on a low-cost FR-4 substrate for aqueous glucose detection. The sensor leverages electric field confinement in inter-ring gaps to transduce glucose-induced permittivity changes into measurable shifts in resonance frequency and reflection coefficient. Experimental results demonstrate a linear, monotonic response across the clinical range up to 250 mg/dL, with a frequency-domain sensitivity of 1.964 MHz/(mg/dL) and amplitude-domain sensitivity of 0.0332 dB/(mg/dL), achieving high coefficients of determination (R2 = 0.9956 and 0.9927, respectively). The design achieves a normalized size of 0.137 λg2, combining high sensitivity and compact size within a scalable platform. Operating in the UWB-adjacent band (2.76–3.25 GHz), the proposed biosensor provides a practical, reproducible, and PCB-compatible solution for next-generation label-free glucose monitoring.