Non-Invasive Fluidic Glucose Detection Based on Dual Microwave Complementary Split Ring Resonators with a Switching Circuit for Environmental Effect Elimination

In this paper, a microwave fluidic glucose sensor based on dual complementary split ring resonators (CSRRs) with a switching circuit is proposed for non-invasive and continuous glucose concentration detection. A CSRR has been designed to detect subtle changes in the dielectric constant of glucose solutions, and the electric field distribution is utilized to determine the effective sensing region. In a well-controlled environment, the glucose concentration can be detected by tracking the transmission coefficient of the designed CSRR. However, because the variations in dielectric constant with the glucose concentration are very small, the environmental factors (i.e., ambient temperature and relative humidity) can be dominant compared to the glucose concentration. To qualify the effect of the environmental factors, the variation in the transmission coefficient of the CSRR has been measured when the ambient temperature condition is varied from 293 K to 313 K and the relative humidity is varied from 30% to 90% inside temperature- and humidity-controlled chamber. Moreover, the environmental effects are calibrated out using two identical CSRRs with the switching circuit: one detects changes in the glucose concentration, while the other operates as a reference for environmental factors. After the elimination of the environmental effects, glucose concentrations in the range of 0 mg/dL to 400 mg/dL have been measured, and the sensitivity is 0.008dB/(100mg/dL). In addition, the reproducibility of the proposed sensor is verified by repeated measurements. It is demonstrated that the proposed sensor can detect glucose concentrations under practical environmental conditions.