# Analysis of Shielding Effectiveness of a Cavity with Internal Dielectric Plate and Apertures
## 3 Verification of Shielding Effectiveness
### Verification of Shielding Effectiveness for Different Aperture Arrays  
We conducted experimental tests on several different hole arrays, with a cavity size of 300 mm \(\times\) 120 mm \(\times\) 300 mm, material set to iron, thickness set to 1 mm, and observation point P located at (0,0,0). Several types of rectangular and circular hole arrays had an area of 2000 mm\({}^{2}\), ignoring the coupling effect between the openings. Porosity can be considered as a superposition of single-hole impedances and can be compared to single holes. The sizes and parameter settings for the different hole arrays are presented in Table 1.  
Through simulation calculations, we obtained shielding effectiveness data for these models. The results indicate that reducing the size of a single hole and increasing the number of hole arrays can significantly improve the shielding effectiveness while maintaining the same opening area. This is because the edge of a single hole is prone to strong scattering \begin{table}
\begin{tabular}{c c c c} \hline
**Test Number** & **Hole Shape** & **Number of Holes** & **Hole Size (mm)** \\ \hline
1 & rectangle & 2 & 100\(\cdot\)10 \\
2 & rectangle & 4 & 50\(\cdot\)10 \\
3 & rectangle & 6 & 50\(\cdot\)6.67 \\
4 & circular & 2 & 17.85 \\
5 & circular & 4 & 12.62 \\
6 & circular & 6 & 10.31 \\ \hline \end{tabular}
\end{table} 
Table 1: Parameter settings for different hole array sizes. Figure 11: Shielding efficiency curves for circular and rectangular openings. and diffraction, making it easier for electromagnetic waves to bypass the shielding material and reducing the shielding effectiveness. The hole array dispersed a single hole into multiple small holes, weakening the scattering and diffraction effects of electromagnetic waves, reducing the possibility of electromagnetic waves bypassing the shielding body. When electromagnetic waves encounter a hole array, their energy is dispersed and absorbed by multiple small holes instead of being concentrated at a single point as with a single hole. The dispersed absorption helps reduce electromagnetic wave leakage and improves shielding effectiveness. Thus, in actual design, a hole array is often used. However, as the number of hole arrays increases, the amplitude gradually decreases, although the shielding effectiveness of the box continues to improve. This means that when the number of hole arrays increases to a certain limit, their shielding effectiveness tends to stabilize, with no significant changes. From Figure 12, it is observed that with the same area of 2000 mm\({}^{2}\), the shielding efficiency of the circular hole array was better than that of the rectangular hole array. Verification of Shielding Effectiveness of a Single Cavity with Apertures and a Built-In Dielectric Board  
To verify the accuracy of the model established in Section 2.3, we constructed a cavity model, as shown in Figure 13. The dimensions of the cavity were 300 mm \(\times\) 120 mm \(\times\) 300 mm, and its thickness was 1 mm. (a) There was a rectangular aperture with a size of 100 mm \(\times\) 20 mm at the center of one side of the cavity. (b) There was a circular aperture with a radius of 25.24 mm at the center of one side of the cavity. Both the rectangular and circular apertures had an area of 2000 mm\({}^{2}\). The cavity material was iron. A mining-specific dielectric board was placed inside the cavity. The thickness of the dielectric board was set to 10 mm; its permittivity was \(\varepsilon_{r}=3\), with a conductivity of 0.22 S/m. The observation point P was located at (0,0,0). The shielding efficiency curves for the circular built-in dielectric plate cavity and the cavity are shown in Figure 14. The graph shows that at 0 to 1 GHz, the curves for the circular dielectric-free plate and the circular dielectric plate nearly overlap, indicating that their shielding effectiveness is similar at 0 to 1 GHz. Figure 12: Shielding efficiency curve for different hole arrays. Figure 13: Simulation model of single-hole cavity with built-in dielectric plate.