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This paper reviews and compares three different strategies for sensitivity improvement in such phase-variation sensors (devoted to material characterization). The considered approaches include line elongation (through meandering), dispersion engineering (by considering slow-wave artificial transmission lines), and reflective-mode sensors based on step-impedance open-ended lines. It is shown that unprecedented sensitivities compatible with small sensing regions are achievable with the latter approach.<\/jats:p>","DOI":"10.3390\/s21041542","type":"journal-article","created":{"date-parts":[[2021,2,23]],"date-time":"2021-02-23T20:19:36Z","timestamp":1614111576000},"page":"1542","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":34,"title":["Planar Phase-Variation Microwave Sensors for Material Characterization: A Review and Comparison of Various Approaches"],"prefix":"10.3390","volume":"21","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1271-3801","authenticated-orcid":false,"given":"Jonathan","family":"Mu\u00f1oz-Enano","sequence":"first","affiliation":[{"name":"CIMITEC, Departament d\u2019Enginyeria Electr\u00f2nica, Universitat Aut\u00f2noma de Barcelona, 08193 Bellaterra, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jan","family":"Coromina","sequence":"additional","affiliation":[{"name":"CIMITEC, Departament d\u2019Enginyeria Electr\u00f2nica, Universitat Aut\u00f2noma de Barcelona, 08193 Bellaterra, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6502-5987","authenticated-orcid":false,"given":"Paris","family":"V\u00e9lez","sequence":"additional","affiliation":[{"name":"CIMITEC, Departament d\u2019Enginyeria Electr\u00f2nica, Universitat Aut\u00f2noma de Barcelona, 08193 Bellaterra, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3962-1480","authenticated-orcid":false,"given":"Lijuan","family":"Su","sequence":"additional","affiliation":[{"name":"CIMITEC, Departament d\u2019Enginyeria Electr\u00f2nica, Universitat Aut\u00f2noma de Barcelona, 08193 Bellaterra, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1106-5059","authenticated-orcid":false,"given":"Marta","family":"Gil","sequence":"additional","affiliation":[{"name":"Departamento Ingenier\u00eda Audiovisual y Comunicaciones, Universidad Polit\u00e9cnica de Madrid, 28031 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2658-2200","authenticated-orcid":false,"given":"Pau","family":"Casacuberta","sequence":"additional","affiliation":[{"name":"CIMITEC, Departament d\u2019Enginyeria Electr\u00f2nica, Universitat Aut\u00f2noma de Barcelona, 08193 Bellaterra, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1494-9167","authenticated-orcid":false,"given":"Ferran","family":"Mart\u00edn","sequence":"additional","affiliation":[{"name":"CIMITEC, Departament d\u2019Enginyeria Electr\u00f2nica, Universitat Aut\u00f2noma de Barcelona, 08193 Bellaterra, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,2,23]]},"reference":[{"key":"ref_1","unstructured":"Mandel, C., Kubina, B., Sch\u00fc\u00dfler, M., and Jakoby, R. (2011, January 10\u201313). Passive chipless wireless sensor for two-dimensional displacement measurement. Proceedings of the 41st European Microwave Conference, Manchester, UK."},{"key":"ref_2","unstructured":"Puentes, M. (2014). Planar Metamaterial Based Microwave Sensor Arrays for Biomedical Analysis and Treatment, Springer."},{"key":"ref_3","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":"2013","journal-title":"IEEE Sens. J."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1109\/MMM.2011.2181448","article-title":"Metamaterial inspired microwave sensors","volume":"13","author":"Mandel","year":"2012","journal-title":"IEEE Microw. Mag."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"3039","DOI":"10.1109\/TIM.2012.2203450","article-title":"Material characterization using complementary split-ring resonators","volume":"61","author":"Boybay","year":"2012","journal-title":"IEEE Trans. Instrum. Meas."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"563","DOI":"10.1109\/LMWC.2014.2318900","article-title":"Complementary split-ring resonators for measuring dielectric constants and loss tangents","volume":"24","author":"Lee","year":"2014","journal-title":"IEEE Microw. Wirel. Compon. Lett."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"247","DOI":"10.1109\/TMTT.2015.2503764","article-title":"Noncontact measurement of complex permittivity and thickness by using planar resonators","volume":"64","author":"Yang","year":"2015","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_8","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_9","doi-asserted-by":"crossref","unstructured":"Salim, A., and Lim, S. (2016). Complementary split-ring resonator-loaded microfluidic ethanol chemical sensor. Sensors, 16.","DOI":"10.3390\/s16111802"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Su, L., Mata-Contreras, J., V\u00e9lez, P., Fern\u00e1ndez-Prieto, A., and Mart\u00edn, F. (2018). Analytical method to estimate the complex permittivity of oil samples. Sensors, 18.","DOI":"10.3390\/s18040984"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Abdolrazzaghi, M., Zarifi, M.H., and Daneshmand, M. (November, January 30). Sensitivity enhancement of split ring resonator based liquid sensors. Proceedings of the 2016 IEEE Sensors, Orlando, FL, USA.","DOI":"10.1109\/ICSENS.2016.7808957"},{"key":"ref_12","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":"2016","journal-title":"IEEE Sens. J."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"7981","DOI":"10.1109\/JSEN.2017.2757027","article-title":"Monitoring solid particle deposition in lossy medium using planar resonator sensor","volume":"17","author":"Zarifi","year":"2017","journal-title":"IEEE Sens. J."},{"key":"ref_14","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":"2017","journal-title":"IEEE Trans. Ind. Electron."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1843","DOI":"10.1109\/TMTT.2018.2791942","article-title":"Strongly enhanced sensitivity in planar microwave sensors based on metamaterial coupling","volume":"66","author":"Abdolrazzaghi","year":"2018","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"139","DOI":"10.1038\/s41598-017-18621-2","article-title":"Noncontact and nonintrusive microwave-microfluidic flow sensor for energy and biomedical engineering","volume":"8","author":"Zarifi","year":"2018","journal-title":"Sci. Rep."},{"key":"ref_17","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_18","doi-asserted-by":"crossref","first-page":"26111","DOI":"10.1109\/ACCESS.2018.2834726","article-title":"Novel Microwave Sensors Based on Split Ring Resonators for Measuring Permittivity","volume":"6","author":"Xu","year":"2018","journal-title":"IEEE Access"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"4382","DOI":"10.1109\/TCSI.2020.3003010","article-title":"Exploiting Sensitivity Enhancement in Micro-wave Planar Sensors Using Intermodulation Products with Phase Noise Analysis","volume":"67","author":"Abdolrazzaghi","year":"2020","journal-title":"IEEE Trans. Circuits Syst. I Regul. Pap."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"4340","DOI":"10.1109\/TMTT.2020.3002996","article-title":"Enhancing the Sensitivity of Dielectric Sensors with Multiple Coupled Complementary Split-Ring Resonators","volume":"68","author":"Albishi","year":"2020","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"806","DOI":"10.1109\/TMTT.2018.2882826","article-title":"A CSRR-Based Sensor for Full Characterization of Magneto-Dielectric Materials","volume":"67","author":"Nayyeri","year":"2019","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"9825","DOI":"10.1109\/JSEN.2020.2991349","article-title":"Gold Coplanar Waveguide Resonator Integrated with a Microfluidic Channel for Aqueous Dielectric Detection","volume":"20","author":"Mohammadi","year":"2020","journal-title":"IEEE Sens. J."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"10545","DOI":"10.1109\/JSEN.2019.2932693","article-title":"Differential Narrow Bandpass Microstrip Filter Design for Material and Liquid Purity Interrogation","volume":"19","author":"Amirian","year":"2019","journal-title":"IEEE Sens. J."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Wiltshire, B.D., Mohammadi, S., and Zarifi, M.H. (2018, January 19\u201322). Integrating 3D Printed Microfluidic Channels with Planar Resonator Sensors for Low Cost and Sensitive Liquid Detection. Proceedings of the 2018 18th International Symposium on Antenna Technology and Applied Electromagnetics (ANTEM), Waterloo, ON, Canada.","DOI":"10.1109\/ANTEM.2018.8572906"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"18","DOI":"10.1016\/j.sna.2014.01.030","article-title":"Two-dimensional alignment and displacement sensor based on movable broadside-coupled split ring resonators","volume":"210","author":"Horestani","year":"2014","journal-title":"Sens. Actuators A Phys."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Naqui, J., Damm, C., Wiens, A., Jakoby, R., Su, L., and Mart\u00edn, F. (2014, January 1\u20136). Transmission lines loaded with pairs of magnetically coupled stepped impedance resonators (SIRs): Modeling and application to microwave sensors. Proceedings of the 2014 IEEE MTT-S International Microwave Symposium, Tampa, FL, USA.","DOI":"10.1109\/MWSYM.2014.6848494"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"68","DOI":"10.1109\/LAWP.2014.2355035","article-title":"Modeling metamaterial transmission lines loaded with pairs of coupled split-ring resonators","volume":"14","author":"Su","year":"2014","journal-title":"IEEE Antennas Wirel. Propag. Lett."},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Su, L., Naqui, J., Mata, J., and Mart\u00edn, F. (2015, January 7\u201312). Dual-band epsilon-negative (ENG) transmission line metamaterials based on microstrip lines loaded with pairs of coupled complementary split ring resonators (CSRRs): Modeling, analysis and applications. Proceedings of the 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, Metamaterials 2015, Oxford, UK.","DOI":"10.1109\/MetaMaterials.2015.7342428"},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Su, L., Naqui, J., Mata-Contreras, J., V\u00e9lez, P., and Mart\u00edn, F. (2015, January 7\u201311). Transmission line metamaterials based on pairs of coupled split ring resonators (SRRs) and complementary split ring resonators (CSRR): A comparison to the light of the lumped element equivalent circuits. Proceedings of the International Conference on Electromagnetics for Advanced Applications, ICEAA 2015, Torino, Italy.","DOI":"10.1109\/ICEAA.2015.7297242"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"154","DOI":"10.1109\/LAWP.2015.2435656","article-title":"Modeling and applications of metamaterial transmission lines loaded with pairs of coupled complementary split-ring resonators (CSRRs)","volume":"15","author":"Su","year":"2015","journal-title":"IEEE Antennas Wirel. Propag. Lett."},{"key":"ref_31","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_32","doi-asserted-by":"crossref","first-page":"4362","DOI":"10.1109\/TMTT.2016.2623311","article-title":"Splitter\/combiner microstrip sections loaded with pairs of complementary split ring resonators (CSRRs): Modeling and optimization for differential sensing applications","volume":"64","author":"Su","year":"2016","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_33","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_34","doi-asserted-by":"crossref","first-page":"5786","DOI":"10.1109\/JSEN.2018.2840691","article-title":"Differential sensors using microstrip lines loaded with two split-ring resonators","volume":"18","author":"Ebrahimi","year":"2018","journal-title":"IEEE Sens. J."},{"key":"ref_35","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_36","doi-asserted-by":"crossref","unstructured":"Ferr\u00e1ndez-Pastor, F.J., Garc\u00eda-Chamizo, J.M., and Nieto-Hidalgo, M. (2017). Electromagnetic differential measuring method: Application in microstrip sensors developing. Sensors, 17.","DOI":"10.3390\/s17071650"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"178","DOI":"10.1109\/JSEN.2019.2941050","article-title":"An analytical method to implement high sensitivity transmission line differential sensors for dielectric constant measurements","volume":"20","author":"Gil","year":"2020","journal-title":"IEEE Sens. J."},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Damm, C., Sch\u00fc\u00dfler, M., Puentes, M., Maune, H., Maasch, M., and Jakoby, R. (2009, January 25\u201328). Artificial transmission lines for high sensitive microwave sensors. Proceedings of the IEEE Sensors Conference, Christchurch, New Zealand.","DOI":"10.1109\/ICSENS.2009.5398538"},{"key":"ref_39","doi-asserted-by":"crossref","unstructured":"V\u00e9lez, P., Mata-Contreras, J., Su, L., Dubuc, D., Grenier, K., and Mart\u00edn, F. (2017, January 20\u201322). Modeling and Analysis of Pairs of Open Complementary Split Ring Resonators (OCSRRs) for Differential Permittivity Sensing. Proceedings of the 2017 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes (IMWS-AMP 2017), Pavia, Italy.","DOI":"10.1109\/IMWS-AMP.2017.8247338"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"48324","DOI":"10.1109\/ACCESS.2018.2867077","article-title":"Highly-Sensitive Microwave Sensors Based on Open Complementary Split Ring Resonators (OCSRRs) for Dielectric Characterization and Solute Concentration Measurement in Liquids","volume":"6","author":"Grenier","year":"2018","journal-title":"IEEE Access"},{"key":"ref_41","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_42","doi-asserted-by":"crossref","first-page":"2562","DOI":"10.1109\/JSEN.2018.2890089","article-title":"Split ring resonator (SRR) based microwave fluidic sensor for electrolyte concentration measurements","volume":"19","author":"Grenier","year":"2019","journal-title":"IEEE Sens. J."},{"key":"ref_43","doi-asserted-by":"crossref","unstructured":"V\u00e9lez, P., Mu\u00f1oz-Enano, J., Gil, M., Mata-Contreras, J., and Mart\u00edn, F. (2019). Differential microfluidic sensors based on dumbbell-shaped defect ground structures in microstrip technology: Analysis, optimization, and applications. Sensors, 19.","DOI":"10.3390\/s19143189"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"690","DOI":"10.1109\/LMWC.2019.2939533","article-title":"Differential sensing based on quasi-microstrip-mode to slot-mode conversion","volume":"29","year":"2019","journal-title":"IEEE Microw. Wirel. Compon. Lett."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"1876","DOI":"10.1109\/TAP.2019.2938609","article-title":"Differential sensor based on electro-inductive wave (EIW) transmission lines for dielectric constant measurements and defect detection","volume":"68","author":"Gil","year":"2020","journal-title":"IEEE Trans. Ant. Propag."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"1312","DOI":"10.1109\/TMTT.2019.2955676","article-title":"Differential-mode to common-mode conversion detector based on rat-race couplers: Analysis and application to microwave sensors and comparators","volume":"68","author":"Gil","year":"2020","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"7545","DOI":"10.3390\/s110807545","article-title":"Novel sensors based on the symmetry properties of split ring resonators (SRRs)","volume":"11","author":"Naqui","year":"2011","journal-title":"Sensors"},{"key":"ref_48","doi-asserted-by":"crossref","unstructured":"Naqui, J., Dur\u00e1n-Sindreu, M., and Mart\u00edn, F. (2012, January 17\u201322). On the symmetry properties of coplanar waveguides loaded with symmetric resonators: Analysis and potential applications. Proceedings of the 2012 IEEE\/MTT-S International Microwave Symposium Digest, Montreal, QC, Canada.","DOI":"10.1109\/MWSYM.2012.6258390"},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"11790","DOI":"10.3390\/s120911790","article-title":"Alignment and position sensors based on split ring resonators","volume":"12","author":"Naqui","year":"2012","journal-title":"Sensors"},{"key":"ref_50","doi-asserted-by":"crossref","unstructured":"Naqui, J., Dur\u00e1n-Sindreu, M., and Mart\u00edn, F. (2013, January 2\u20137). Transmission lines loaded with bisymmetric resonators and applications. Proceedings of the IEEE MTT-S International Microwave Symposium Digest, Seattle, WA, USA.","DOI":"10.1109\/MWSYM.2013.6697368"},{"key":"ref_51","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":"2012","journal-title":"IEEE Sens. J."},{"key":"ref_52","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_53","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_54","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_55","doi-asserted-by":"crossref","first-page":"620","DOI":"10.1049\/el.2014.0572","article-title":"Two-dimensional displacement and alignment sensor based on reflection coefficients of open microstrip lines loaded with split ring resonators","volume":"50","author":"Horestani","year":"2014","journal-title":"Electron. Lett."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"939","DOI":"10.1109\/JSEN.2013.2295518","article-title":"Angular displacement and velocity sensors based on electric-LC (ELC) loaded microstrip lines","volume":"14","author":"Naqui","year":"2013","journal-title":"IEEE Sens. J."},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"9628","DOI":"10.3390\/s150509628","article-title":"Angular displacement and velocity sensors based on coplanar waveguides (CPWs) loaded with S-shaped split ring resonators (S-SRR)","volume":"15","author":"Naqui","year":"2015","journal-title":"Sensors"},{"key":"ref_58","doi-asserted-by":"crossref","unstructured":"Naqui, J., and Mart\u00edn, F. (2016, January 22\u201327). Application of broadside-coupled split ring resonator (BC-SRR) loaded transmission lines to the design of rotary encoders for space applications. Proceedings of the IEEE MTT-S International Microwave Symposium, San Francisco, CA, USA.","DOI":"10.1109\/MWSYM.2016.7540017"},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"4450","DOI":"10.1109\/TMTT.2017.2693981","article-title":"Application of split ring resonator (SRR) loaded transmission lines to the design of angular displacement and velocity sensors for space applications","volume":"65","author":"Herrojo","year":"2017","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_60","doi-asserted-by":"crossref","first-page":"7055","DOI":"10.1109\/JSEN.2018.2853643","article-title":"Detecting the rotation direction in contactless angular velocity sensors implemented with rotors loaded with multiple chains of resonators","volume":"18","author":"Herrojo","year":"2018","journal-title":"IEEE Sens. J."},{"key":"ref_61","doi-asserted-by":"crossref","unstructured":"Coromina, J., Mu\u00f1oz-Enano, J., V\u00e9lez, P., Ebrahimi, A., Scott, J., Ghorbani, K., and Mart\u00edn, F. (2021, January 12\u201314). Capacitively-Loaded Slow-Wave Transmission Lines for Sensitivity Improvement in Phase-Variation Permittivity Sensors. Proceedings of the 50th European Microwave Conference, Utrecht, The Netherlands.","DOI":"10.23919\/EuMC48046.2021.9338025"},{"key":"ref_62","doi-asserted-by":"crossref","first-page":"308","DOI":"10.1109\/TMTT.2020.3023728","article-title":"On the sensitivity of reflective-mode phase variation sensors based on open-ended stepped-impedance transmission lines: Theoretical analysis and experimental validation","volume":"69","author":"Gil","year":"2021","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_63","doi-asserted-by":"crossref","first-page":"2864","DOI":"10.1109\/JSEN.2020.3023848","article-title":"Highly sensitive phase variation sensors based on step-impedance coplanar waveguide (CPW) transmission lines","volume":"21","author":"Su","year":"2021","journal-title":"IEEE Sens. J."},{"key":"ref_64","doi-asserted-by":"crossref","unstructured":"Casacuberta, P., Mu\u00f1oz-Enano, J., V\u00e9lez, P., Su, L., Gil, M., and Mart\u00edn, F. (2020). Highly sensitive reflective-mode detectors and dielectric constant sensors based on open-ended stepped-impedance transmission lines. Sensors, 20.","DOI":"10.3390\/s20216236"},{"key":"ref_65","doi-asserted-by":"crossref","first-page":"1598","DOI":"10.1109\/TMTT.2019.2957369","article-title":"A Highly Sensitive Planar Microwave Sensor for Detecting Direction and Angle of Rotation","volume":"68","author":"Jha","year":"2020","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_66","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":"Shaterian","year":"2020","journal-title":"IEEE Sens. J."},{"key":"ref_67","doi-asserted-by":"crossref","first-page":"189565","DOI":"10.1109\/ACCESS.2020.3031032","article-title":"A reflective-mode phase-variation displacement sensor","volume":"8","author":"Su","year":"2020","journal-title":"IEEE Access"},{"key":"ref_68","unstructured":"Pozar, D.M. (2011). Microwave Engineering, John Wiley. [4th ed.]."},{"key":"ref_69","doi-asserted-by":"crossref","unstructured":"Mart\u00edn, F. (2015). Artificial Transmission Lines for RF and Microwave Applications, John Wiley.","DOI":"10.1002\/9781119058403"},{"key":"ref_70","doi-asserted-by":"crossref","unstructured":"Caloz, C., and Itoh, T. (2005). Electromagnetic Metamaterials: Transmission Line Theory and Microwave Applications, Wiley-IEEE Press.","DOI":"10.1002\/0471754323"},{"key":"ref_71","doi-asserted-by":"crossref","unstructured":"Eleftheriades, G., and Balmain, K.G. (2005). Negative Refraction Metamaterials: Fundamental Principles and Applications, Wiley-IEEE Press.","DOI":"10.1002\/0471744751"},{"key":"ref_72","unstructured":"Caloz, C., and Itoh, T. (2003, January 8\u201313). Novel microwave devices and structures based on the transmission line approach of metamaterials. Proceedings of the IEEE MTT-S International Microwave Symposium Digest, Philadelphia, PA, USA."},{"key":"ref_73","doi-asserted-by":"crossref","first-page":"083503","DOI":"10.1063\/1.2176850","article-title":"Electroinductive waves in chains of complementary metamaterial elements","volume":"88","author":"Beruete","year":"2006","journal-title":"Appl. Phys. Lett."},{"key":"ref_74","first-page":"366","article-title":"Slow wave structures","volume":"Volume 19","author":"Webster","year":"1999","journal-title":"Encyclopedia of Electrical and Electronics Engineering"},{"key":"ref_75","doi-asserted-by":"crossref","first-page":"86","DOI":"10.1109\/75.275589","article-title":"A novel coplanar slow-wave structure","volume":"4","year":"1994","journal-title":"IEEE Microw. Guided Wave Lett."},{"key":"ref_76","doi-asserted-by":"crossref","first-page":"1235","DOI":"10.1109\/TMTT.2016.2638843","article-title":"Design of capacitively-loaded coupled line bandpass filters with compact size and spurious suppression","volume":"65","author":"Orellana","year":"2017","journal-title":"IEEE Trans. Microw. Theory. Tech."},{"key":"ref_77","doi-asserted-by":"crossref","first-page":"6","DOI":"10.1109\/7260.975717","article-title":"Miniaturized wilkinson power dividers utilizing capacitive loading","volume":"12","author":"Scardelletti","year":"2002","journal-title":"IEEE Microw. Wirel. Compon. Lett."},{"key":"ref_78","doi-asserted-by":"crossref","first-page":"2119","DOI":"10.1109\/TMTT.2003.817442","article-title":"Compact planar microstripline branch-line and rat-race couplers","volume":"51","author":"Eccleston","year":"2003","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_79","doi-asserted-by":"crossref","first-page":"4136","DOI":"10.1109\/TMTT.2006.886155","article-title":"Application of electromagnetic bandgaps (EBGs) to the design of ultra wide band pass filters (UWBPFs) with good out-of-band performance","volume":"54","author":"Bonache","year":"2006","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_80","doi-asserted-by":"crossref","first-page":"2981","DOI":"10.1109\/TMTT.2009.2034219","article-title":"Transdirectional coupled-line couplers implemented by periodical shunt capacitors","volume":"57","author":"Shie","year":"2009","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_81","doi-asserted-by":"crossref","first-page":"629","DOI":"10.1002\/mmce.20901","article-title":"Synthesis of slow-wave structures based on capacitive-loaded lines through aggressive space mapping (ASM)","volume":"25","author":"Orellana","year":"2015","journal-title":"Int. J. RF Microw. Comput. Aided Eng."},{"key":"ref_82","doi-asserted-by":"crossref","first-page":"2822","DOI":"10.1002\/mop.30837","article-title":"Size reduction and harmonic suppression in branch line couplers implemented by means of capacitively-loaded slow-wave transmission lines","volume":"59","author":"Coromina","year":"2017","journal-title":"Microw. Opt. Technol. Lett."},{"key":"ref_83","doi-asserted-by":"crossref","first-page":"67310","DOI":"10.1109\/ACCESS.2020.2985569","article-title":"Branch line couplers with small size and harmonic suppression based on non-periodic step impedance shunt stub (SISS) loaded lines","volume":"8","author":"Coromina","year":"2020","journal-title":"IEEE Access"},{"key":"ref_84","doi-asserted-by":"crossref","first-page":"77","DOI":"10.1002\/mop.20052","article-title":"Guided-wave characteristics of periodic microstrip lines with inductive loading: Slow-wave and bandstop behaviors","volume":"41","author":"Zhu","year":"2004","journal-title":"Microw. Opt. Technol. Lett."},{"key":"ref_85","doi-asserted-by":"crossref","first-page":"2383","DOI":"10.1109\/TMTT.2010.2058281","article-title":"Generalized miniaturization method for coupled-line bandpass filters by reactive loading","volume":"58","author":"Lee","year":"2010","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_86","doi-asserted-by":"crossref","unstructured":"V\u00e9lez, P., Selga, J., Bonache, J., and Mart\u00edn, F. (2016, January 4\u20136). Slow-wave inductively-loaded electromagnetic bandgap (EBG) coplanar waveguide (CPW) transmission lines and application to compact power dividers. Proceedings of the 2016 46th European Microwave Conference (EuMC), London, UK.","DOI":"10.1109\/EuMC.2016.7824288"},{"key":"ref_87","doi-asserted-by":"crossref","first-page":"44","DOI":"10.1007\/s00339-016-0675-6","article-title":"EBG-based transmission lines with slow-wave characteristics and application to miniaturization of microwave components","volume":"123","author":"Selga","year":"2016","journal-title":"Appl. Phys. A"},{"key":"ref_88","doi-asserted-by":"crossref","first-page":"530","DOI":"10.1017\/S1759078717001350","article-title":"Slow wave coplanar waveguides based on inductive and capacitive loading and application to compact and harmonic suppressed power splitters","volume":"10","author":"Aznar","year":"2018","journal-title":"Int. J. Microw. Wirel. Technol."},{"key":"ref_89","doi-asserted-by":"crossref","first-page":"2374","DOI":"10.1002\/mop.31377","article-title":"Harmonic suppression in branch-line couplers based on slow wave transmission lines with simultaneous inductive and capacitive loading","volume":"60","author":"Selga","year":"2018","journal-title":"Microw. Opt. Tech. Lett."},{"key":"ref_90","doi-asserted-by":"crossref","unstructured":"Ebrahimi, A., Coromina, J., Mu\u00f1oz-Enano, J., V\u00e9lez, P., Scott, J., Ghorbani, K., and Mart\u00edn, F. (2021). Highly sensitive phase-variation dielectric constant sensor based on a capacitively-loaded slow-wave transmission line. IEEE Trans. Circuits Syst., submitted for publication.","DOI":"10.1109\/TCSI.2021.3074570"},{"key":"ref_91","doi-asserted-by":"crossref","unstructured":"Mu\u00f1oz-Enano, J., Casacuberta, P., Su, L., V\u00e9lez, P., Gil, M., and Mart\u00edn, F. (2020, January 25\u201328). Open-Ended-Line Reflective-Mode Phase-Variation Sensors for Dielectric Constant Measurements. Proceedings of the IEEE Sensors 2020, Rotterdam, The Netherlands.","DOI":"10.1109\/SENSORS47125.2020.9278857"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/4\/1542\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T05:26:56Z","timestamp":1760160416000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/4\/1542"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,2,23]]},"references-count":91,"journal-issue":{"issue":"4","published-online":{"date-parts":[[2021,2]]}},"alternative-id":["s21041542"],"URL":"https:\/\/doi.org\/10.3390\/s21041542","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,2,23]]}}}