## 2 Numerical Simulations  
### Simulation of a Unidirectional Probe  
Earlier in [18], the authors presented and theoretically studied the design of a probe that has significant prospects for creating a device for accurate non-invasive monitoring of glucose levels. We suggested that it would be more expedient to make the probe unidirectional, in order, firstly, to avoid unnecessary radiation, and, secondly, to focus it in order to maximize the signal penetrating into the medium. Based on the design of the microwave probe previously developed by the authors, a numerical simulation of this design was carried out in the case of unidirectional radiation. To do this, we took a metal plate, which we attached to one of the sides of the probe. Since the probe is completely symmetrical, the choice of a particular side is not important. The resulting model is shown in Figure 1. The dimensions correspond to the previously presented probe in [18]. The metal plate had a diameter of 160 mm. The parameter \"normal\" is selected as the external space, which has the value of dielectric and magnetic permeability equal to 1, which corresponds to vacuum. Figure 1 shows the result of calculating the distribution of the electric field near a unidirectional probe at frequencies of 2 GHz (a) and 10 GHz (b). The graduation of the radiation measurement scale corresponds to the scale shown in Figure 1.  
Figure 1: CST model of a near-field microwave probe (left). Electric field distribution of the near-field probe at a frequency of 2 GHz (**a**) and 10 GHz (**b**). It can be seen from the figures that the probe has an extended field without external radiation backward. The use of a metal plate can increase the penetration depth of the near field. So, if for a bidirectional probe the maximum possible the penetration depth at low frequencies was 18 cm, in the case of a unidirectional probe, the near-field radiation is prolonged to 20 cm with a maximum radiation of 21.2 V/m. The electric field strength was taken into account at a frequency of 2 GHz this frequency was chosen based on the calculation of the minimum value when choosing the 2-10 GHz range. As the frequency increases, the near-field diverges in three directions, while the central near-field radiation still has a prolonged form in comparison with the bidirectional probe. It can also be seen that at high frequencies the electric field decays faster, which can be related to both the wavelength and the design of the probe. Figure 2 shows the result of calculating the distribution of the electric field and magnetic field near the radiator. According to the calculation for this configuration, the maximum possible length of the near-field reactive field at low frequencies is 18 cm, as in the bidirectional case. Next, it was necessary to simulate the interaction of this probe with the environment for further comparison of the sensors. As which was considered a flat-layered structure consisting of: skin, fat, blood, muscle and bone. The thickness of the layers was as follows: skin--1 mm, fat--0.5 mm, blood--2.5 mm, muscles--15 mm, bone--10 mm. These thicknesses are due to previous research. To calculate the dielectric parameters, the formula given in the article was used [19]. The formula is:  
\[\varepsilon(\omega)=\varepsilon_{\infty}+\sum_{n}\frac{\Delta\varepsilon_{n}} {1+(j\omega\tau_{n})^{1-\varepsilon_{n}}}+\frac{\sigma_{i}}{j\omega\varepsilon _{0}} \tag{1}\]  
where, \(\varepsilon_{\infty}\), \(\varepsilon\)-are the \"static\" and \"infinite frequency\" of the dielectric permittivity, \(\omega\) is the angular frequency, \(\tau\) is the time constant, \(\alpha\) is the exponent parameter takes values from 0 to 1, \(\varepsilon(\omega)\) is the complex dielectric permittivity. The values for each of the layers of the simulated flat-layered structure are shown in Table 1 for each of the materials. Figure 2: Field distribution E-field (**a**) and H-field (**b**) near a unidirectional probe.