## 3 Shielding of Electromagnetic Field
When an incident wave strikes the interface between two dielectrics, a portion of the incident wave's energy reflects (\(E_{\textit{rrf}}\)), while another portion of the incident wave's energy is absorbed (\(E_{\textit{abs}}\)) within the material of the plate. The remaining energy of the incident wave passes through to the other side of the plate (transmitted wave). It is established that the intensity of the magnetic field absorbed by the plate is defined as follows [2]:  
\[|H_{\textit{abs}}|=\frac{|E_{\textit{abs}}|}{Z_{S}} \tag{3}\]  
While \(H_{\textit{abs}}\) represents the intensity of the magnetic field absorbed within the board, \(E_{\textit{abs}}\) denotes the intensity of the electric field absorbed within the board, and \(Z_{S}\) is the impedance of the board material. As seen in Figure 3, the interface between two dielectrics, air-board, at point X = 0 is marked. Furthermore, it is possible to define EX = 0\(-\) and EX = 0+. The index X = 0\(-\) indicates the field to the left of point X = 0, and the index X = 0+ indicates the field to the right of point X = 0, making it easier to distinguish the incident electromagnetic wave from the field beyond the interface of the two dielectrics. The relationship between the incident and reflected waves can be defined based on the energy of the incident wave, \(E_{\textit{dop}}\), and the reflection coefficient, \(R\), according to the following formula [2]:  
\[\Big{|}E_{\textit{ref}}\Big{|}=\Big{|}E_{\textit{dop}}\Big{|}.R \tag{4}\]  
It is noted that the reflection coefficient \(R\) is given by the formula [2]:  
\[R=\frac{Z_{S}-Z_{0}}{Z_{S}+Z_{0}} \tag{5}\]  
Equation (6) dictates that the energy \(E_{\textit{abs}}\) absorbed by the wave can be calculated using the incident wave's energy, denoted as \(E_{\textit{dop}}\), and the absorption coefficient, referred to as \(A\). \[E_{\textit{abs}}=\Big{|}E_{\textit{dop}}\Big{|}.A \tag{6}\]  
If the material is not ideal and has a specific conductivity \(\sigma\
eq 0\), the incident wave that hits this material is absorbed within its structure [2]:  
\[|E_{\textit{abs}}(X)|=|E_{\textit{abs}}(X=0)|e^{\frac{-X}{T}} \tag{7}\]  
Figure 3: The calibration process. Drawing from Figure 2 and the previously outlined formulas, the energy of the transmitted wave, _Epr_, can be articulated as [2]:  
\[\left|E_{pr}\right|=\left|E_{dop}\right|\frac{2Z_{S}}{Z_{0}+Z_{S}}\left(\frac{2Z_ {S}}{Z_{0}+Z_{S}}\right)e^{\frac{-t}{\sigma}} \tag{8}\]  
For the scenario where \(Z_{S}\) is much less than \(Z_{0}\), it holds that _Epr_ can be expressed as follows:  
\[Z_{0}=\sqrt{\frac{\mu_{0}}{\varepsilon_{0}}} \tag{2}\]0  
Using the previously described equations, it is possible to express the shielding effectiveness (\(SE\)), which is considered a measure of the quality of the shielding material. Manufacturers of protective gear provide \(SE\) values. Shielding effectiveness can be expressed as the ratio of the incident wave \(E_{dop}\) to the transmitted wave \(E_{pr}\)[2]:  
\[Z_{0}=\sqrt{\frac{\mu_{0}}{\varepsilon_{0}}} \tag{2}\]1  
After expressing \(E_{dop}\) and \(E_{pr}\), the \(SE\) can be articulated as:  
\[Z_{0}=\sqrt{\frac{\mu_{0}}{\varepsilon_{0}}} \tag{2}\]2  
where \(R\) is the reflection coefficient of the electromagnetic wave and \(A\) is the absorption coefficient of the electromagnetic wave. Some works in the literature [2,8] state that a portion of the reflection coefficient comprises the coefficient of multiple reflections \(M\) within the shielding material. When an electromagnetic wave propagates through the same space, it maintains its direction of travel. However, when it encounters the interface between two materials, the law of incidence and reflection applies. The same occurs when an electromagnetic wave hits the vacuum/shielding material interface. Part of the transmitted wave is reflected, and part of it penetrates the shielding material. This portion travels through the shielding material in an altered direction until it reaches the interface of the shielding material/vacuum (edge of the shielding material) again.