{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,18]],"date-time":"2026-03-18T14:30:03Z","timestamp":1773844203770,"version":"3.50.1"},"reference-count":56,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2021,10,13]],"date-time":"2021-10-13T00:00:00Z","timestamp":1634083200000},"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>In this paper, a very high sensitivity microwave-based planar microfluidic sensor is presented. Sensitivity enhancement is achieved and described theoretically and experimentally by eliminating any extra parasitic capacitance not contributing to the sensing mechanism. The sensor consists of a microstrip transmission line loaded with a series connected shunt LC resonator. A microfluidic channel is attached to the area of the highest electric field concentration. The electric field distribution and, therefore, the resonance characteristics are modified by applying microfluidic dielectric samples to the sensing area. The sensor performance and working principle are described through a circuit model analysis. A device prototype is fabricated, and experimental measurements using water\/ethanol and water\/methanol solutions are presented for validation of the sensing mathematical model.<\/jats:p>","DOI":"10.3390\/s21206811","type":"journal-article","created":{"date-parts":[[2021,10,13]],"date-time":"2021-10-13T21:48:39Z","timestamp":1634161719000},"page":"6811","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":57,"title":["Extremely Sensitive Microwave Microfluidic Dielectric Sensor Using a Transmission Line Loaded with Shunt LC Resonators"],"prefix":"10.3390","volume":"21","author":[{"given":"Haneen","family":"Abdelwahab","sequence":"first","affiliation":[{"name":"School of Engineering, RMIT University, Melbourne, VIC 3001, Australia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0858-4958","authenticated-orcid":false,"given":"Amir","family":"Ebrahimi","sequence":"additional","affiliation":[{"name":"School of Engineering, RMIT University, Melbourne, VIC 3001, Australia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8578-7786","authenticated-orcid":false,"given":"Francisco J.","family":"Tovar-Lopez","sequence":"additional","affiliation":[{"name":"School of Engineering, RMIT University, Melbourne, VIC 3001, Australia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6622-569X","authenticated-orcid":false,"given":"Grzegorz","family":"Beziuk","sequence":"additional","affiliation":[{"name":"School of Engineering, RMIT University, Melbourne, VIC 3001, Australia"}]},{"given":"Kamran","family":"Ghorbani","sequence":"additional","affiliation":[{"name":"School of Engineering, RMIT University, Melbourne, VIC 3001, Australia"}]}],"member":"1968","published-online":{"date-parts":[[2021,10,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2787","DOI":"10.1109\/TCSI.2021.3074570","article-title":"Highly sensitive phase-variation dielectric constant sensor based on a capacitively-loaded slow-wave transmission line","volume":"68","author":"Ebrahimi","year":"2021","journal-title":"IEEE Trans. Circuits Syst. I Regul. Pap."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1109\/MMM.2011.2181448","article-title":"Metamaterial inspired microwave sensors","volume":"13","author":"Schueler","year":"2012","journal-title":"IEEE Microw. Mag."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"9706","DOI":"10.1109\/JSEN.2020.2990484","article-title":"Rotation sensor based on the cross-polarized excitation of split ring resonators (SRRs)","volume":"20","author":"Horestani","year":"2020","journal-title":"IEEE Sens. J."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1153","DOI":"10.1109\/JSEN.2012.2231065","article-title":"Displacement sensor based on diamond-shaped tapered split ring resonator","volume":"13","author":"Horestani","year":"2013","journal-title":"IEEE Sens. J."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"3014","DOI":"10.1109\/JSEN.2013.2264804","article-title":"Rotation sensor based on horn-shaped split ring resonator","volume":"13","author":"Horestani","year":"2013","journal-title":"IEEE Sens. J."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"4700","DOI":"10.1109\/TMTT.2013.2285356","article-title":"Transmission lines loaded with bisymmetric resonators and their application to angular displacement and velocity sensors","volume":"61","author":"Naqui","year":"2013","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"2609","DOI":"10.1109\/JSEN.2014.2313625","article-title":"Metamaterial-inspired rotation sensor with wide dynamic range","volume":"14","author":"Ebrahimi","year":"2014","journal-title":"IEEE Sens. J."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"10647","DOI":"10.1109\/JSEN.2021.3063112","article-title":"Phase-variation microwave sensor for permittivity measurements based on a high-impedance half-wavelength transmission line","volume":"21","author":"Su","year":"2021","journal-title":"IEEE Sens. J."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"12189","DOI":"10.1109\/JSEN.2021.3062290","article-title":"Single-frequency amplitude-modulation sensor for dielectric characterization of solids and microfluidics","volume":"21","author":"Ebrahimi","year":"2021","journal-title":"IEEE Sens. J."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"185","DOI":"10.1109\/JSEN.2019.2941753","article-title":"Dual-mode resonator for simultaneous permittivity and thickness measurement of dielectrics","volume":"20","author":"Ebrahimi","year":"2020","journal-title":"IEEE Sens. J."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Ebrahimi, A., Beziuk, G., Scott, J., and Ghorbani, K. (2020). Microwave differential frequency splitting sensor using magnetic-LC resonators. Sensors, 20.","DOI":"10.3390\/s20041066"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1626","DOI":"10.1109\/TIE.2017.2733449","article-title":"A Microwave ring resonator sensor for early detection of breaches in pipeline coatings","volume":"65","author":"Zarifi","year":"2018","journal-title":"IEEE Trans. Ind. Electron."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2632","DOI":"10.1109\/TIM.2014.2313415","article-title":"A generalized rectangular cavity approach for determination of complex permittivity of materials","volume":"63","author":"Jha","year":"2014","journal-title":"IEEE Trans. Instrum. Meas."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"7181","DOI":"10.1109\/JSEN.2015.2469683","article-title":"Design and application of the CSRR-based planar sensor for noninvasive measurement of complex permittivity","volume":"12","author":"Ansari","year":"2015","journal-title":"IEEE Sens. J."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"2011","DOI":"10.1109\/TMTT.2006.873623","article-title":"A waveguide-based two-step approach for measuring complex permittivity tensor of uniaxial composite materials","volume":"54","author":"Akhtar","year":"2006","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"3864","DOI":"10.1109\/TMTT.2016.2610423","article-title":"Transmission lines loaded with pairs of stepped impedance resonators: Modeling and application to differential permittivity measurements","volume":"64","author":"Naqui","year":"2016","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"323","DOI":"10.1109\/JSEN.2016.2631618","article-title":"Robust ultra-high resolution microwave planar sensor using fuzzy neural network approach","volume":"17","author":"Abdolrazzaghi","year":"2017","journal-title":"IEEE Sens. J."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"6589","DOI":"10.1109\/JSEN.2017.2747764","article-title":"Microwave microfluidic sensor based on a microstrip splitter\/combiner configuration and split ring resonators (SRRs) for dielectric characterization of liquids","volume":"17","author":"Su","year":"2017","journal-title":"IEEE Sens. J."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1149","DOI":"10.1109\/LMWC.2018.2875996","article-title":"Transmission lines terminated with LC resonators for differential permittivity sensing","volume":"28","author":"Ebrahimi","year":"2018","journal-title":"IEEE Microw. Wirel. Compon. Lett."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"1175","DOI":"10.1109\/TMTT.2019.2953580","article-title":"3-D printed microfluidic sensor in SIW technology for liquids\u2019 characterization","volume":"68","author":"Rocco","year":"2020","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"27928","DOI":"10.1109\/ACCESS.2021.3058575","article-title":"Highly sensitive reflective-mode phase-variation permittivity sensor based on a coplanar waveguide terminated with an open complementary split ring resonator (OCSRR)","volume":"9","author":"Su","year":"2021","journal-title":"IEEE Access"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"173","DOI":"10.1016\/j.snb.2015.08.074","article-title":"Electromagnetic-based ethanol chemical sensor using metamaterial absorber","volume":"222","author":"Yoo","year":"2016","journal-title":"Sens. Actuators B Chem."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"3246","DOI":"10.1109\/TMTT.2009.2034226","article-title":"Integrated broadband microwave and microfluidic sensor dedicated to bioengineering","volume":"57","author":"Grenier","year":"2009","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"4130","DOI":"10.1109\/TMTT.2019.2931555","article-title":"Locally strong-coupled microwave resonator using PEMC boundary for distant sensing applications","volume":"67","author":"Nosrati","year":"2019","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"13247","DOI":"10.1109\/JSEN.2021.3071839","article-title":"Highly sensitive microwave sensor for high precision sensing of water contamination in mineral oil","volume":"21","author":"Baghelani","year":"2021","journal-title":"IEEE Sens. J."},{"key":"ref_26","first-page":"11492","article-title":"Artificial intelligence assisted noncontact microwave sensor for multivariable biofuel analysis","volume":"68","author":"Baghelani","year":"2021","journal-title":"IEEE Sens. J."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"2562","DOI":"10.1109\/JSEN.2018.2890089","article-title":"Split ring resonator-based microwave fluidic sensors for electrolyte concentration measurements","volume":"19","author":"Velez","year":"2019","journal-title":"IEEE Sens. J."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"621","DOI":"10.1109\/LMWC.2015.2451354","article-title":"Liquid sensing using active feedback assisted planar microwave resonator","volume":"25","author":"Zarifi","year":"2015","journal-title":"IEEE Microw. Wirel. Compon. Lett."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"2766","DOI":"10.1109\/JSEN.2017.2682266","article-title":"High-Q sensor based on symmetrical split ring resonator with spurlines for solids material detection","volume":"17","author":"Alahnomi","year":"2017","journal-title":"IEEE Sens. J."},{"key":"ref_30","first-page":"1438","article-title":"A microwave method for dielectric characterization measurement of small liquids using a metamaterialbased sensor","volume":"18","author":"Liu","year":"2018","journal-title":"Sens. Actuators B Chem."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"114501","DOI":"10.1063\/1.3021109","article-title":"Characterization of miniaturized metamaterial resonators coupled to planar transmission lines through parameter extraction","volume":"104","author":"Aznar","year":"2008","journal-title":"J. Appl. Phys."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"233","DOI":"10.1016\/j.sna.2012.10.027","article-title":"Metamaterial-based microfluidic sensor for dielectric characterization","volume":"189","author":"Withayachumnankul","year":"2013","journal-title":"Sens. Actuators A Phys."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"2023","DOI":"10.1109\/TMTT.2013.2255885","article-title":"Recent advances in microwave-based dielectric spectroscopy at the cellular level for cancer investigations","volume":"61","author":"Grenier","year":"2013","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"4171","DOI":"10.1109\/TMTT.2012.2222660","article-title":"Accurate nanoliter liquid characterization up to 40 GHz for biomedical applications: Toward noninvasive living cells monitoring","volume":"60","author":"Chen","year":"2012","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1109\/TIM.2021.3073438","article-title":"Accurate microwave cavity sensing technique for dielectric testing of arbitrary length samples","volume":"70","author":"Jha","year":"2021","journal-title":"IEEE Trans. Instrum. Meas."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"1561","DOI":"10.1016\/j.snb.2017.08.169","article-title":"Sensitivity enhancement in planar microwave active-resonator using metal organic framework for CO2 detection","volume":"255","author":"Zarifi","year":"2018","journal-title":"Sens. Actuators B Chem."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"3016","DOI":"10.1109\/TMTT.2015.2472019","article-title":"Design and in vitro interference test of microwave noninvasive blood glucose monitoring sensor","volume":"63","author":"Choi","year":"2015","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"679","DOI":"10.1109\/TMTT.2014.2300066","article-title":"Novel microwave microfluidic sensor using a microstrip split-ring resonator","volume":"62","author":"Abduljabar","year":"2014","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"689","DOI":"10.1109\/TMTT.2014.2299514","article-title":"Improved split-ring resonator for microfluidic sensing","volume":"62","author":"Rowe","year":"2014","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_40","first-page":"185","article-title":"Differential microwave sensor for characterization of glycerole-water solutions","volume":"231","author":"Ebrahimi","year":"2020","journal-title":"Sens. Actuators B Chem."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"1444","DOI":"10.1109\/TMTT.2012.2187066","article-title":"A self-sustained microwave system for dielectric-constant measurement of lossy Split ring resonator-based microwave fluidic sensors for electrolyte concentration measurements liquids","volume":"60","author":"Sekar","year":"2012","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"045003","DOI":"10.1063\/1.5021684","article-title":"A hollow coaxial cable Fabry\u2013P\u00e9rot resonator for liquid dielectric constant measurement","volume":"89","author":"Zhu","year":"2018","journal-title":"Rev. Sci. Instrum."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"1830","DOI":"10.1109\/TMTT.2019.2959757","article-title":"High Q microwave microfluidic sensor using a central gap ring resonator","volume":"68","author":"Hamzah","year":"2020","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"531","DOI":"10.1109\/LMWC.2020.2980756","article-title":"Differential microwave resonator sensor reveals glucose-dependent growth profile of E. coli on solid agar","volume":"30","author":"Jain","year":"2020","journal-title":"IEEE Microw. Wirel. Compon. Lett."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"111662","DOI":"10.1016\/j.sna.2019.111662","article-title":"Microwave reflective biosensor for glucose level detection in aqueous solutions","volume":"301","author":"Ebrahimi","year":"2020","journal-title":"Sens. Actuators A Phys."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"18742","DOI":"10.1109\/JSEN.2021.3090050","article-title":"Noninvasive glucose sensing in aqueous solutions using an active split-ring resonator","volume":"21","author":"Abdolrazzaghi","year":"2021","journal-title":"IEEE Sens. J."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"1345","DOI":"10.1109\/JSEN.2013.2295312","article-title":"High-sensitivity metamaterial-inspired sensor for microfluidic dielectric characterization","volume":"14","author":"Ebrahimi","year":"2014","journal-title":"IEEE Sens. J."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"972","DOI":"10.1109\/TMTT.2012.2231877","article-title":"A microwave and microfluidic planar resonator for efficient and accurate complex permittivity characterization of aqueous solutions","volume":"61","author":"Chretiennot","year":"2013","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"2080","DOI":"10.1109\/TMTT.2020.2978051","article-title":"Integration of interdigitated electrodes in split-ring resonator for detecting liquid mixtures","volume":"68","author":"Bao","year":"2020","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"1201","DOI":"10.1109\/LMWC.2020.3029060","article-title":"An ultrahigh sensitivity microwave sensor for microfluidic applications","volume":"30","author":"Fan","year":"2020","journal-title":"IEEE Microw. Wirel. Compon. Lett."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"18756","DOI":"10.1109\/JSEN.2021.3090086","article-title":"Ultrahigh-sensitivity microwave microfluidic sensors based on modified complementary electric-LC and split-ring resonator structures","volume":"21","author":"Wu","year":"2021","journal-title":"IEEE Sens. J."},{"key":"ref_52","first-page":"1843","article-title":"Strongly enhanced sensitivity in planar microwave sensors based on metamaterial coupling","volume":"66","author":"Abdolrazzaghi","year":"2018","journal-title":"IEEE Microw. Mag."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"4269","DOI":"10.1109\/TMTT.2019.2932737","article-title":"Ultrahigh-sensitivity microwave sensor for microfluidic complex permittivity measurement","volume":"67","author":"Ebrahimi","year":"2019","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_54","doi-asserted-by":"crossref","unstructured":"Mu\u00f1oz-Enano, J., Martel, J., V\u00e9lez, P., Medina, F., Su, L., and Mart\u00edn, F. (2021). Parametric analysis of the edge capacitance of uniform slots and application to frequency-variation permittivity sensors. Appl. Sci., 11.","DOI":"10.3390\/app11157000"},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"4441","DOI":"10.1063\/1.471197","article-title":"Microwave dielectric characterization of binary mixtures of water methanol and ethanol","volume":"104","author":"Bao","year":"1996","journal-title":"J. Chem. Phys."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"5876","DOI":"10.1109\/JSEN.2020.2973196","article-title":"Differential microwave micorfluidic sensor based on microstrip complementary split-ring resonator (MCSRR) structure","volume":"20","author":"Gan","year":"2020","journal-title":"IEEE Sens. J."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/20\/6811\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T07:12:47Z","timestamp":1760166767000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/20\/6811"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,10,13]]},"references-count":56,"journal-issue":{"issue":"20","published-online":{"date-parts":[[2021,10]]}},"alternative-id":["s21206811"],"URL":"https:\/\/doi.org\/10.3390\/s21206811","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,10,13]]}}}