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Sensors 2018, 18(1), 143; https://doi.org/10.3390/s18010143

Microfluidic High-Q Circular Substrate-Integrated Waveguide (SIW) Cavity for Radio Frequency (RF) Chemical Liquid Sensing

School of Electrical and Electronics Engineering, College of Engineering, Chung-Ang University, 84-Heukseok-ro, Dongjak-gu, Seoul 156-756, Korea
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Received: 16 October 2017 / Revised: 27 December 2017 / Accepted: 4 January 2018 / Published: 6 January 2018
(This article belongs to the Special Issue Microfluidic Sensors)
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Abstract

In this study, a high-Q circular substrate-integrated waveguide (SIW) cavity resonator is proposed as a non-contact and non-invasive radio frequency (RF) sensor for chemical sensing applications. The design of the structure utilizes SIW technology along with a circular shape to achieve a high unloaded Q factor, which is one of the important requirements for RF sensors. The resonant frequency of the proposed circular SIW cavity sensor changes when a liquid material or a chemical (microliters) is inserted in the sensitive area of the structure. The sensing of liquid materials with different permittivities is accomplished via the perturbation of the electric fields in the SIW configuration. When a microwell that is 4 mm in radius is installed vertically through the center of the bare circular SIW cavity, the operating frequency varies from 5.26 to 5.34 GHz. Similarly, when the microwell contains ethanol, the frequency shifts from 5.26 to 5.18 GHz, and the amplitude of reflection coefficient is shifted from −29 dB to −17 dB; when the microwell contains mixing deionized (DI)-water, the frequency moves from 5.26 to 4.98 GHz (which is also 0% Ethanol in our study), and the amplitude of reflection coefficient is shifted from −29 dB to −8 dB. A high unloaded Q factor is maintained throughout all experimental results. To demonstrate our idea, different concentrations of ethanol are tested and recorded. The experimental validation yields a close agreement between the simulations and the measurements. View Full-Text
Keywords: chemical sensor; SIW; circular cavity; RF sensor; wireless sensor; ethanol chemical sensor; SIW; circular cavity; RF sensor; wireless sensor; ethanol
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Memon, M.U.; Lim, S. Microfluidic High-Q Circular Substrate-Integrated Waveguide (SIW) Cavity for Radio Frequency (RF) Chemical Liquid Sensing. Sensors 2018, 18, 143.

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