Figure 3: (a) Measured microwave reflection coefficient change Δ 𝑆 1 1 plotted as a function of the glucose concentrations from DI water to 300 mg/ml with the interval of 50 mg/ml at 4.6 GHz (high concentration range). The inset (a) shows 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) 50 mg/ml, (c) 100 mg/ml, (d) 150 mg/ml, (e) 200 mg/ml, (f) 250 mg/ml, and (g) 300 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 (0–300 mg/ml) as a function of operation frequency in the 4-5 GHz range.