{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,30]],"date-time":"2026-09-30T17:05:56Z","timestamp":1790787956538,"version":"4.1.0"},"reference-count":79,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2025,12,24]],"date-time":"2025-12-24T00:00:00Z","timestamp":1766534400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>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 \u03bbg2, combining high sensitivity and compact size within a scalable platform. Operating in the UWB-adjacent band (2.76\u20133.25 GHz), the proposed biosensor provides a practical, reproducible, and PCB-compatible solution for next-generation label-free glucose monitoring.<\/jats:p>","DOI":"10.3390\/s26010131","type":"journal-article","created":{"date-parts":[[2025,12,24]],"date-time":"2025-12-24T16:41:19Z","timestamp":1766594479000},"page":"131","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["A Linear and High-Sensitivity Microwave Biosensor on a FR-4 Substrate for Aqueous Glucose Monitoring Using a Concentric Square-Shaped Split-Ring Resonator"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0009-0007-8135-6736","authenticated-orcid":false,"given":"Khouloud","family":"Jomaa","sequence":"first","affiliation":[{"name":"Electronics and Micro-Electronic Laboratory (LE\u00b5E), Bd de L\u2019environnement, Monastir 5000, Tunisia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2782-0570","authenticated-orcid":false,"given":"Sehmi","family":"Saad","sequence":"additional","affiliation":[{"name":"RF2S Spectrum Solutions, 18 Street of the Fa\u00efencerie, 33300 Bordeaux, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6205-4643","authenticated-orcid":false,"given":"Darine","family":"Kaddour","sequence":"additional","affiliation":[{"name":"University Grenoble-Alpes, Grenoble-INP\/LCIS, 26000 Valence, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2385-4845","authenticated-orcid":false,"given":"Pierre","family":"Lema\u00eetre-Auger","sequence":"additional","affiliation":[{"name":"University Grenoble-Alpes, Grenoble-INP\/LCIS, 26000 Valence, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4404-5986","authenticated-orcid":false,"given":"Hatem","family":"Garrab","sequence":"additional","affiliation":[{"name":"Electronics and Micro-Electronic Laboratory (LE\u00b5E), Bd de L\u2019environnement, Monastir 5000, Tunisia"},{"name":"Higher Institute of Applied Sciences and Technology of Sousse, University of Sousse, Street Taher Ben Achour, Sousse 4003, Tunisia"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,12,24]]},"reference":[{"key":"ref_1","unstructured":"Magliano, D.J., and Boyko, E.J. 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