# 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
(**A**) Rectangular opening (**B**) Circular opening. In Figure 15, we compare the shielding effectiveness curves for the rectangular built-in dielectric plate cavity and the cavity. For an empty cavity, especially around a specific frequency point (0.7 GHz), the shielding efficiency decreased significantly owing to the generation of cavity resonance. The built-in dielectric plate cavity also experienced a slight displacement of the resonance point, with a relatively small impact compared to that of the cavity. It improved the shielding efficiency near the resonance point to some extent. However, the effect of the frequency domain far from the resonance point was relatively limited. After electromagnetic waves are coupled into the cavity, when they encounter a dielectric plate, some energy is absorbed owing to dielectric loss, which weakens the electric field strength inside the cavity and significantly improves the shielding efficiency. For electromagnetic waves incident near the resonant point, owing to their greater energy coupled into the cavity, the absorption effect of the dielectric plate is particularly prominent, resulting in greater suppression on the resonant point and significantly enhancing the shielding efficiency near the resonant point. Compared with electromagnetic waves incident far from the resonant point, the energy coupled into the cavity was lower, and the absorption effect of the dielectric plate was not significant. Thus, its shielding effectiveness was almost the same as that without a dielectric plate. In Table 2, we set the thickness of the circular and rectangular perforated dielectric plates to 10 mm, 20 mm, and 30 mm while keeping the structure, material, size, and other parameters of the cavity consistent. Figure 16 shows that as the thickness of the dielectric plate increases, the resonant frequency of the cavity gradually decreases compared to the resonant frequency of 0.7 GHz at a thickness of 1 mm. This is because an increase in the thickness of the dielectric plate prolongs the oscillation period of the electromagnetic waves inside the cavity. In Figure 17, as the thickness of the dielectric plate increases, the shielding efficiency near the resonant frequency point of the cavity improves to a certain extent. Figure 14: Comparison of shielding effectiveness of circular plates with and without dielectric plates. Figure 15: Comparison of shielding effectiveness of rectangular plates with and without dielectric plates. Figure 18 and 19 show the shielding effectiveness curves for dielectric plates fixed at three different positions inside the cavity, at the rear, lower, and side ends, with rectangular and circular openings. With consistency in cavity structure, material, size, and other parameters, it is observed from Figures 18 and 19 that for the same observation point, when the dielectric plate is placed at the lower end of the cavity, the shielding effectiveness at the resonance point is slightly better than that at the rear and side ends. The shielding effectiveness of the three positions at a distance from the resonance point was approximately equivalent. Thus, to effectively improve the shielding efficiency, a dielectric plate can be placed at the lower end of the cavity. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Number** & **Perforated Shape** &
\begin{tabular}{c} **Dielectric Plate** \\ **Thickness (mm)** \\ \end{tabular} & **Cavity Material** \\ \hline
1 & circular & 10 & Iron \\
2 & circular & 20 & Iron \\
3 & circular & 30 & Iron \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameter settings. Figure 16: Shielding efficiency curve for rectangular perforated dielectric plates with different thicknesses. Figure 17: Shielding efficiency curve for dielectric plates with different circular opening thicknesses. Figure 18: Shielding efficiency curve for rectangular dielectric plate position change.