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Sensors 2018, 18(3), 910;

A Compact Microwave Microfluidic Sensor Using a Re-Entrant Cavity

Engineering College, University of Al-Qadisiyah, Al-Qadisiyah, Diwaniyah 58001, Iraq
Engineering College, University of Basrah, Basrah, Baghdad Street Qarmat Ali, IQ-61002, Iraq
Centre for High Frequency Engineering, Cardiff University, Wales, CF10 3AT Cardiff, UK
Author to whom correspondence should be addressed.
Received: 12 January 2018 / Revised: 15 February 2018 / Accepted: 5 March 2018 / Published: 19 March 2018
(This article belongs to the Special Issue Microfluidic Sensors)
PDF [3181 KB, uploaded 19 March 2018]


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’s performance has also been assessed for analysis of segmented flow using water and oil. The samples’ 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. View Full-Text
Keywords: re-entrant microwave cavity; microfluidic sensing; dielectric properties; segmented flow re-entrant microwave cavity; microfluidic sensing; dielectric properties; segmented flow

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Hamzah, H.; Abduljabar, A.; Lees, J.; Porch, A. A Compact Microwave Microfluidic Sensor Using a Re-Entrant Cavity. Sensors 2018, 18, 910.

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