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Sensors 2019, 19(3), 715; https://doi.org/10.3390/s19030715

An Interdigital Capacitor for Microwave Heating at 25 GHz and Wideband Dielectric Sensing of nL Volumes in Continuous Microfluidics

1
Division ESAT-TELEMIC, KU Leuven, Kasteelpark Arenberg 10 box 2444, 3001 Leuven, Belgium
2
imec, imec PERSYBE Group, Kapeldreef 75, 3001 Heverlee, Belgium
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Received: 14 December 2018 / Revised: 24 January 2019 / Accepted: 7 February 2019 / Published: 10 February 2019
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Abstract

This paper proposes a miniature microwave-microfluidic chip based on continuous microfluidics and a miniature interdigital capacitor (IDC). The novel chip consists of three individually accessible heaters, three platinum temperature sensors and two liquid cooling and mixing zones. The IDC is designed to achieve localized, fast and uniform heating of nanoliter volumes flowing through the microfluidic channel. The heating performance of the IDC located on the novel chip was evaluated using a fluorescent dye (Rhodamine B) diluted in demineralized water on a novel microwave-optical-fluidic (MOF) measurement setup. The MOF setup allows simultaneous microwave excitation of the IDC by means of a custom-made printed circuit board (connected to microwave equipment) placed in a top stage of a microscope, manipulation of liquid flowing through the channel located over the IDC with a pump and optical inspection of the same liquid flowing over the IDC using a fast camera, a light source and the microscope. The designed IDC brings a liquid volume of around 1.2 nL from room temperature to 100 °C in 21 ms with 1.58 W at 25 GHz. Next to the heating capability, the designed IDC can dielectrically sense the flowing liquid. Liquid sensing was evaluated on different concentration of water-isopropanol mixtures, and a reflection coefficient magnitude change of 6 dB was recorded around 8.1 GHz, while the minimum of the reflection coefficient magnitude shifted in the same frequency range for 60 MHz. View Full-Text
Keywords: continuous microfluidics; dielectric sensing; microwave heating; interdigital capacitor continuous microfluidics; dielectric sensing; microwave heating; interdigital capacitor
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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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Markovic, T.; Bao, J.; Maenhout, G.; Ocket, I.; Nauwelaers, B. An Interdigital Capacitor for Microwave Heating at 25 GHz and Wideband Dielectric Sensing of nL Volumes in Continuous Microfluidics. Sensors 2019, 19, 715.

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