Abnormal trend for noninvasive BGL sensors using phase shift technology

Abstract

For the first time, this paper finds and investigates the abnormal trend for the noninvasive detection of blood glucose levels (BGLs) based on phase technology. To support the findings, the basic microwave structure of a grounded coplanar waveguide (GCPW) was utilized. In the theoretical research, a GCPW material under test transmission line model was developed to analyze how the dielectric properties of glucose solutions impact the surface electric field distribution of the GCPW. From this model, we derived the relationship between the phase shift of the GCPW and the dielectric properties of the glucose solution, revealing that an inverse trend may appear at different frequency points. The simulation results obtained through the finite element method aligned well with the theoretical analysis, showing a strong correlation between the phase shift of the S parameters and the concentration of the glucose solution. After the test platform was established, preliminary experiments were conducted when the BGLs were varied from 0 to 8.57 mg/ml. The results demonstrate that the phase shift of S11 is highly correlated with glucose concentration. Specifically, at the frequency of 2.27 GHz, the phase shift decreases as glucose concentration increases, whereas at 2.80 GHz, the phase shift increases with rising glucose concentration. Additionally, a linear regression prediction model was proposed to enhance the practical feasibility for noninvasive BGLs’ measurement in future applications.