## 3 Shielding of Electromagnetic Field  
Electromagnetic waves traveling perpendicularly along the z axis and encountering a barrier for shielding are both reflected and partially absorbed. When considering shield effectiveness, waves that approach vertically demonstrate poorer performance due to their easier penetration through the barrier. In contrast, electromagnetic waves striking at a specific angle offer improved shielding properties, as they are more readily reflected, resulting in reduced penetration through the shielding obstacle. In the case of electromagnetic waves with lower frequencies, the electric and magnetic components of electromagnetic waves are considered separately. In subsequent sections, the components of the electromagnetic wave are derived, having the following significance: the index 'dop' for the incident wave,'ref' for the reflected wave, 'abs' for the absorbed wave, and 'pr' for the transmitted wave--Figure 2[21, 22]. The authors in Refs. [2; 3] presented research focused on the effectiveness of shielding the electromagnetic field. The research was focused on two brick samples with different air-gap sizes. The paper also describes the measurement method and procedure in further detail. The results indicate that bricks with the same thickness but different air-gap dimensions exhibit different shielding efficiency values. The experiment demonstrates that a larger air-gap size results in lower shielding efficiency. For instance, at a frequency of 3 GHz, the shielding efficiency for the air gap of Sample 1 is \(SE\) = 5.8 dB, and for the air gap of Sample 2, \(SE\) = 7.8 dB. Shielding efficiency comprises the absorption and reflection of the electromagnetic field. However, this experiment does not confirm that the absorption/reflection ratio of the electromagnetic field must also change. While the shielding efficiency value is altered, the ratio of \(R\) (reflection) and \(A\) (absorption) could remain constant. In [4], authors experimented with a combination of shielding paint and some building materials. Specifically, they used polystyrene POLYFORM with a thickness of 5 cm, YSHiELD HSF 64 shielding paint, water, and BauKleber building glue of class C1T. The measurements were conducted in the frequency range from 1 GHz to 9 GHz with a step size of 50 MHz. The HSF 64 paint was mixed with water and glue in a ratio of 1 kg-275 g of paint. According to the manufacturer, the shielding effectiveness of HSF 64 is 39 dB. The results from the measurements indicate that the combination of these materials led to a decrease in shielding effectiveness, with a maximum reduction of approximately 5 dB. The authors concluded that the combination of this type of paint with other materials, especially glue and water, is not suitable and is not recommended. This conclusion suggests that when selecting materials for shielding purposes, it is important to consider their combination, as some combinations can significantly reduce the expected shielding effectiveness [2; 3; 4]. The intensity of the magnetic field, \(H_{dop}\), of the incoming wave on a plate is determined by the ratio of the incoming wave's electric field intensity, \(E_{dop}\), to the impedance of free space. Free space is defined as the space through which the wave propagates freely. Thus, it is not the impedance of the shielding material but, from a practical perspective, it is the impedance of air. However, for the analysis of shielding effectiveness, the free space is considered as a vacuum [2]:  
\[\left|H_{dop}\right|=\frac{\left|E_{dop}\right|}{Z_{0}} \tag{1}\]  
The impedance of free space is determined by the square root of the ratio of vacuum permeability to vacuum permittivity [2]:  
\[Z_{0}=\sqrt{\frac{\mu_{0}}{\varepsilon_{0}}} \tag{2}\]  
Figure 2: Incident, reflected, and absorbed waves.