{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,6]],"date-time":"2026-02-06T15:55:26Z","timestamp":1770393326472,"version":"3.49.0"},"reference-count":35,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2026,2,4]],"date-time":"2026-02-04T00:00:00Z","timestamp":1770163200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Shanxi Provincial Department of Education\u2019s Higher Education Institution Science and Technology Innovation Program","award":["2023L357"],"award-info":[{"award-number":["2023L357"]}]},{"DOI":"10.13039\/501100007926","name":"North University of China","doi-asserted-by":"crossref","id":[{"id":"10.13039\/501100007926","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100006768","name":"Taiyuan University of Technology","doi-asserted-by":"crossref","id":[{"id":"10.13039\/501100006768","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>This paper proposes and experimentally validates a label-free microdroplet concentration detector based on a quad-resonator metamaterial. The device exploits the linear relationship between the dielectric constant of a binary mixed solution and its concentration, mapping concentration information to absorption frequency shifts with a sensitivity of 28.53 GHz\/RIU. System modeling was performed through full-wave simulation. Experimental results demonstrate a highly linear relationship between resonance frequency shift and concentration across ethanol, water, and ethanol\u2013water solutions. The relative deviation between simulation and measurement is less than 3%, validating the model\u2019s reliability and the robustness of the detection principle. This detector supports rapid non-contact sample replacement without requiring chemical labeling or specialized packaging. It can be mass-produced on standard PDMS substrates, with each unit reusable for &gt;50 cycles. With a single measurement time of &lt;30 s, it meets high-throughput detection demands. Featuring low power consumption, high precision, and scalability, this device holds broad application prospects in point-of-care diagnostics, online process monitoring, and resource-constrained scenarios. Future work will focus on achieving simultaneous multi-component detection via multi-resonator arrays and integrating chip-level wireless readout modules to further enhance portability and system integration.<\/jats:p>","DOI":"10.3390\/s26031013","type":"journal-article","created":{"date-parts":[[2026,2,4]],"date-time":"2026-02-04T12:51:56Z","timestamp":1770209516000},"page":"1013","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Label-Free Microdroplet Concentration Detector Based on a Quadruple Resonant Ring Metamaterial"],"prefix":"10.3390","volume":"26","author":[{"given":"Wenjin","family":"Guo","sequence":"first","affiliation":[{"name":"School of Information and Communication Engineering, North University of China, Taiyuan 030051, China"},{"name":"Department of Electronic Engineering, Taiyuan Institute of Technology, Taiyuan 030024, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yinuo","family":"Cheng","sequence":"additional","affiliation":[{"name":"School of Information and Communication Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0002-2291-4455","authenticated-orcid":false,"given":"Jian","family":"Li","sequence":"additional","affiliation":[{"name":"School of Information and Communication Engineering, North University of China, Taiyuan 030051, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,2,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"538","DOI":"10.1070\/PU1968v010n04ABEH003699","article-title":"The electrodynamics of substances with simultaneously negative values of \u03b5 and \u03bc","volume":"10","author":"Veselago","year":"1968","journal-title":"Sov. 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