Ultrahigh-Sensitivity Microwave Sensor for Microfluidic Complex Permittivity Measurement

• Published in: IEEE transactions on microwave theory and techniques Vol. 67; no. 10; pp. 4269 - 4277
• Main Authors: Ebrahimi, Amir, Scott, James, Ghorbani, Kamran
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Capacitors; Circuits; Complex permittivity; Dielectric measurement; Ethanol; Frequency shift; Integrated circuit modeling; microfluidic sensor; Microfluidics; Microstrip; Microstrip transmission lines; microwave sensor; Microwave sensors; planar resonators; Resonators; Sensitivity; Sensors; Transmission lines
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2019.2932737

The conventional resonant-type microwave microfluidic sensors made of planar resonators suffer from limited sensitivities. This is due to the existence of several distributed capacitors in their structure, where just one of them acts as a sensing element. This article proposes a very high-sensitivity microwave sensor made of a microstrip transmission line loaded with a shunt-connected series LC resonator. A large sensitivity for dielectric loadings is achieved by incorporating just one capacitor in the resonator structure. Applying sample liquids to the microfluidic channel implemented in the capacitive gap area of the sensor modifies the capacitor value. This is translated to a resonance frequency shift from which the liquid sample is characterized. The sensor performance and working principle are described through a circuit model analysis. Finally, a device prototype is fabricated, and experimental measurements using water/ethanol solutions are presented for verification of the sensing principle.