{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T17:24:42Z","timestamp":1790702682637,"version":"4.1.0"},"reference-count":25,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2018,3,19]],"date-time":"2018-03-19T00:00:00Z","timestamp":1521417600000},"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>A miniaturized 2.4 GHz re-entrant cavity has been designed, manufactured and tested as a sensor for microfluidic compositional analysis. It has been fully evaluated experimentally with water and common solvents, namely methanol, ethanol, and chloroform, with excellent agreement with the expected behaviour predicted by the Debye model. The sensor\u2019s performance has also been assessed for analysis of segmented flow using water and oil. The samples\u2019 interaction with the electric field in the gap region has been maximized by aligning the sample tube parallel to the electric field in this region, and the small width of the gap (typically 1 mm) result in a highly localised complex permittivity measurement. The re-entrant cavity has simple mechanical geometry, small size, high quality factor, and due to the high concentration of electric field in the gap region, a very small mode volume. These factors combine to result in a highly sensitive, compact sensor for both pure liquids and liquid mixtures in capillary or microfluidic environments.<\/jats:p>","DOI":"10.3390\/s18030910","type":"journal-article","created":{"date-parts":[[2018,3,20]],"date-time":"2018-03-20T06:57:11Z","timestamp":1521529031000},"page":"910","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":43,"title":["A Compact Microwave Microfluidic Sensor Using a Re-Entrant Cavity"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3315-2513","authenticated-orcid":false,"given":"Hayder","family":"Hamzah","sequence":"first","affiliation":[{"name":"Engineering College, University of Al-Qadisiyah, Al-Qadisiyah, Diwaniyah 58001, Iraq"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ali","family":"Abduljabar","sequence":"additional","affiliation":[{"name":"Engineering College, University of Basrah, Basrah, Baghdad Street Qarmat Ali, IQ-61002, Iraq"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jonathan","family":"Lees","sequence":"additional","affiliation":[{"name":"Centre for High Frequency Engineering, Cardiff University, Wales, CF10 3AT Cardiff, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Adrian","family":"Porch","sequence":"additional","affiliation":[{"name":"Centre for High Frequency Engineering, Cardiff University, Wales, CF10 3AT Cardiff, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2018,3,19]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"322","DOI":"10.1016\/j.sna.2010.04.017","article-title":"RF evanescent-mode cavity resonator for passive wireless sensor applications","volume":"161","author":"Zhao","year":"2010","journal-title":"Sens. Actuators A Phys."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"55","DOI":"10.1016\/j.sna.2011.07.007","article-title":"Detection of microdroplet size and speed using capacitive sensors","volume":"171","author":"Elbuken","year":"2011","journal-title":"Sens. Actuators A Phys."},{"key":"ref_3","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_4","doi-asserted-by":"crossref","first-page":"2159","DOI":"10.1109\/22.884209","article-title":"Accurate microwave resonant method for complex permittivity measurements of liquids","volume":"48","author":"Yu","year":"2000","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"3995","DOI":"10.1109\/TMTT.2006.883655","article-title":"Measurements of permittivity, dielectric loss tangent, and resistivity of float-zone silicon at microwave frequencies","volume":"54","author":"Krupka","year":"2006","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Bonde, S., D\u2019Silva, R., Gupte, V., John, M., Fernandes, F., and Kotrashetti, A. (2011, January 16\u201318). 2.4 GHz cavity notch filter for UWB radio. Proceedings of the 2011 Annual IEEE India Conference (INDICON), Hyderabad, India.","DOI":"10.1109\/INDCON.2011.6139462"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"44","DOI":"10.1016\/j.physc.2005.05.010","article-title":"High Tc superconductor re-entrant cavity filter structures","volume":"425","author":"Pandit","year":"2005","journal-title":"Phys. C Supercond."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Krupka, J., Geyer, R.G., Baker-Jarvis, J., and Ceremuga, J. (1996, January 23\u201326). Measurements of the complex permittivity of microwave circuit board substrates using split dielectric resonator and reentrant cavity techniques. Proceedings of the Seventh International Conference on Dielectric Materials, Measurements and Applications, Bath, UK.","DOI":"10.1049\/cp:19960982"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"129","DOI":"10.6028\/jres.056.017","article-title":"A re-entrant cavity for measurement of complex permeability in the very-high-frequency region","volume":"56","author":"Harrington","year":"1956","journal-title":"Res. Natl. Bur. Stand."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Shindo, Y., Kato, K., Tsuchiya, K., Yabuhara, T., Shigihara, T., Iwazaki, R., Uzuka, T., and Takahashi, H. (2007, January 22\u201326). Heating properties of re-entrant resonant applicator for brain tumor by electromagnetic heating modes. Proceedings of the 2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Lyon, France.","DOI":"10.1109\/IEMBS.2007.4353112"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Ishihara, Y., Endo, Y., Ohwada, H., and Wadamori, N. (2007, January 22\u201326). Noninvasive thermometry in a reentrant resonant cavity applicator. Proceedings of the 2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Lyon, France.","DOI":"10.1109\/IEMBS.2007.4352582"},{"key":"ref_12","unstructured":"Barroso, J.J., Castro, P.J., Neto, J.P.L., and Aguiar, O.D. (2005, January 25). Reentrant cylindrical cavities. Proceedings of the 2005 SBMO\/IEEE MTT-S International Conference on Microwave and Optoelectronics, Brasilia, Brazil."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1139","DOI":"10.1109\/TDEI.2007.4339473","article-title":"Microwave measurements of dielectric properties using a closed cylindrical cavity dielectric resonator","volume":"14","author":"Sheen","year":"2007","journal-title":"IEEE Trans. Dielectr. Electr. Insul."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1041","DOI":"10.1109\/TMTT.1981.1130496","article-title":"Precise Calculations and Measurements on the complex dielectric constant of lossy materials using TM010 cavity perturbation techniques","volume":"29","author":"Li","year":"1981","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"2120","DOI":"10.1109\/TIM.2005.854249","article-title":"Measurement of dielectric parameters of small samples at X-band frequencies by cavity perturbation technique","volume":"54","author":"Verma","year":"2005","journal-title":"IEEE Trans. Instrum. Meas."},{"key":"ref_16","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_17","doi-asserted-by":"crossref","first-page":"904","DOI":"10.1016\/j.snb.2013.02.099","article-title":"Efficient microwave heating of microfluidic systems","volume":"181","author":"Morgan","year":"2013","journal-title":"Sens. Actuators B Chem."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Khan, A.S. (2014). Microwave Engineering Concepts and Fundamentals, CRC Press.","DOI":"10.1201\/b16689"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Zhang, K., and Li, D. (1998). Electromagnetic Theory for Microwaves and Optpelectronics, Springer.","DOI":"10.1007\/978-3-662-03553-5"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"344","DOI":"10.1109\/TMTT.1958.1125205","article-title":"General treatment of klystron resonant cavities","volume":"6","author":"Fujisawa","year":"1958","journal-title":"IRE Trans. Microw. Theory Tech."},{"key":"ref_21","first-page":"182","article-title":"Microwave cavities for plasma diagnostics","volume":"4","author":"Raptis","year":"1969","journal-title":"J. Microw. Power Electromagn. Energy"},{"key":"ref_22","unstructured":"Pozar, D.M. (2011). Microwave Engineering, John Wiley & Sons, Inc."},{"key":"ref_23","unstructured":"Collin, R.E. (1960). Field Theory of Guided Waves, McGraw-Hill Book Company, Inc."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"44","DOI":"10.1109\/PROC.1974.9384","article-title":"Microwave heating in the food industry","volume":"62","author":"Engtsson","year":"1974","journal-title":"Proc. IEEE"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"943","DOI":"10.1007\/s12034-009-0001-4","article-title":"Prospects of microwave processing: An overview","volume":"32","author":"Das","year":"2009","journal-title":"Bull. Mater. Sci."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/18\/3\/910\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T14:57:38Z","timestamp":1760194658000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/18\/3\/910"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2018,3,19]]},"references-count":25,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2018,3]]}},"alternative-id":["s18030910"],"URL":"https:\/\/doi.org\/10.3390\/s18030910","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2018,3,19]]}}}