Figure 2: (a) Measured microwave reflection coefficient change Δ 𝑆 1 1 plotted as a function of the glucose concentrations from DI water to 10 mg/ml with the interval of 1 mg/ml at 4.6 GHz (low concentration range). A solid line shows a fit to (1) and (4) with 𝑍 0 = 5 0  Ω. The inset shows the real-time diagram of the microwave reflection coefficient with two signal levels: for air, that is, empty tube and for (a) DI water or glucose solution with the glucose concentration of (b) 1 mg/ml, (c) 2 mg/ml, (d) 3 mg/ml, (e) 4 mg/ml, (f) 5 mg/ml, (g) 6 mg/ml, (h) 7 mg/ml, (i) 8 mg/ml, (j) 9 mg/ml, and (k) 10 mg/ml. (b) The dependences of (a) real (left axis) and (b) imaginary (right axis) parts of the complex relative permittivity on the glucose concentration (low concentration range: 0–10 mg/ml) as a function of operation frequency in the 4-5 GHz range.