## 2 Numerical Simulations
### Simulation of a Unidirectional Probe
Apart from the resonance at 3.6 GHz the similarity of these  
Figure 5: Model of numerical experiments with a flat layered biological medium and a unidirectional probe. Figure 6: Frequency dependence of the reflected signal from change in the distance between the metal plate and the probe. values is observed. The reflected signal at 2.6 GHz is similar to the bidirectional transmitter at 2.9 GHz. Comparing the values obtained for different distances of the metal plate from the probe, it was concluded that the best among the presented results is the distance of 1 mm. At this distance, we got two resonances at a low frequency of 2.6 GHz and a high frequency of 9 GHz. Increasing the distance further reduces resonance at low frequencies, while increasing values at high frequencies. Further modeling was carried out taking into account the measurements made above and the selected distance of the metal plate from the probe of 1 mm. It can be seen, however, that the reflected signal at 3.6 GHz remains unchanged. This fact is explained by the resonance at the inner diameter of the probe, which is 90 mm, which, when converted to frequency, gives 3.5 GHz. Because of this, a resonance occurs at the same frequency when the distance of the metal plate from the probe changes, but even in this case, small shifts of the resonance in frequency occur. Determination of the sensitivity of the unidirectional probe was carried out by changing the layer with the dielectric properties of the blood at various glucose concentrations (0, 4, 5.3, 7.5 mmol/L). The resulting reflected signal data is shown in Figure 3:0  
Two resonance peaks can be observed in the graphs (Figure 7) at 2.65 GHz and 8.9 GHz. The values for the reflected signal at a glucose concentration of 0 mmol/L are maximally knocked out at the second peak in region 2, therefore further research was focused on the frequency range 2-4 GHz for region 1. Figure 8 is a graph enlarged in scale for region 1. Figure 3:1 Frequency dependence of the reflected signal for various glucose concentrations. Figure 3:2 Frequency response of the reflected signal for various glucose concentrations. It can be observed that when the glucose concentration changes, the reflected signal changes both in amplitude and in frequency. So the values of the amplitude of the reflected signal were: 0 mmol/L- \(-\)30.819 dB, 4 mmol/L- \(-\)33.073 dB, 5.3 mmol/L- \(-\)35.762 dB, 7.5 mmol/L- \(-\)41.094 dB. Thus, the sensitivity of the probe is 1.5-2.7 dB/(mmol/L). The frequency values for each of the concentrations were: 0 mmol/L- 2.75 GHz, 4 mmol/L- 2.67 GHz, 5.3 mmol/L- 2.66 GHz, 7.5 mmol/L- 2.65 GHz. The frequency sensitivity of the probe was 5-7 MHz/(mmol/L). For the frequency shift of the reflected signal, it is possible to distinguish to regions: first one, from 0 to 4 mmol/L with a shift of 20 MHz /mmol/L, second one, from 4 to 8 mmol/L with a shift of 5 MHz /mmol/L. The obtained simulation results indicate a high sensitivity of the probe. Also, in addition to amplitude changes, frequency changes were also observed for each concentration. Studies of blood glucose levels in two parameters significantly increase the accuracy of the data obtained. We also considered the VSWR values for this frequency range at a concentration value of 4 mmol/L. The results are shown in Figure 3:3 As can be seen from the graph, the values do not exceed 3 rel. units on the VSWR scale over the entire considered range. Further, before conducting an experimental study, it was necessary to create a physical model of the biological environment (phantom) with the most approximate electrophysiological values calculated in numerical modeling for each material (layer).