Fluidic Glucose Measurement Based on a Differential Microwave Sensing System With Combination of Multistepped-Impedance Transmission Lines

• Published in: IEEE sensors journal 2024-09, Vol.24 (18), p.28805-28817
• Main Authors: Wu, Wen-Jing, Shang, Lina, Zhao, Wen-Sheng, Wang, Wensong
• Format: Article
• Language: English
• Subjects: Curve fitting; Differential structure; Error detection; Glucose; Impedance; Mathematical analysis; Mathematical models; Microwave circuits; Microwave oscillators; microwave sensing system; multistepped-impedance transmission lines (MSITLs); Parameter sensitivity; Permittivity; Phase detectors; phase of reflection coefficient; Phase shifters; Power dividers; Power transmission lines; Radio frequency; Reflectance; Sensors; Transmission line measurements; Transmission lines
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2024.3434970

A differential microwave sensing system based on short-ended multistepped-impedance transmission lines (MSITLs) for measuring blood glucose concentration in binary solution is put forward in this article. The phase of reflection coefficient of MSITL is adopted to detect glucose concentration. In order to obtain the high sensitivity, the change ratio of phase of reflection coefficient and glucose concentration should be maximum. The derivative mathematical model between the phase of reflection coefficient and glucose concentration/permittivity should be established, the optimized geometrical parameter values are derived by solving the maximum value of the derivative mathematical model. Then, a three-stepped-impedance transmission line is implemented to demonstrate the correctness of analysis. The differential structure is obtained by symmetrically replicate the MSITL. After finishing the design of MSITLs, a reflective RF oscillator is designed to transform the relationship between the phase of reflection coefficient and glucose concentration/permittivity into the relationship between oscillation frequency and glucose concentration/permittivity. Then, a power divider, phase shifter, and phase detector are added to constitute the microwave sensing system. The microwave sensing system can translate the bearing between oscillation frequency and glucose concentration into the relationhip between output dc voltage and glucose concentration. Finally, the fitting curve formula is obtained to predict the unknown glucose concentration. In measurement, the microwave sensing system shows an average sensitivity of about 53.897~\mu V/(mg/dL), and the maximum error is about 10.38%. In addition, the minimum detectable concentration is about 12.5 mg/dL, and the resolution is several times higher than other reported ones. The proposed microwave sensing system is a good choice in the application of characterizing liquid solutions.