# Analysis of Shielding Effectiveness of a Cavity with Internal Dielectric Plate and Apertures
## 3 Verification of Shielding Effectiveness  
### Verification of Shielding Effectiveness for Single-Hole Cavity  
To verify the feasibility of the theoretical analysis, we simulated the shielded cavity using HFSS software. The cavity model is shown in Figure 9. The cavity size is 300 mm \(\times\) 120 mm \(\times\) 300 mm; the material is iron, and the thickness is 1 mm. There is a 100 mm \(\times\) 20 mm rectangular opening on the surface of the cavity, with observation point P located at (0,0,0).  
In the HFSS simulation setup, we performed a frequency sweep analysis to simulate the propagation characteristics of electromagnetic waves within a specific frequency range. We set the frequency range of the plane-wave interference source to start at 0.1 GHz and end at 1 GHz. To ensure the accuracy and continuity of the results, we set a step size of 0.02 GHz. HFSS conducted multiple simulation calculations within this frequency range at intervals of 0.02 GHz. We used a discrete sweep-frequency type; HFSS simulated specified frequency points.  
To simulate a free and open radiation space, we set up an air box at the periphery to represent an infinite space, allowing electromagnetic waves to propagate freely within it. The boundary conditions for the air box were chosen as radiation boundary conditions, allowing electromagnetic waves to propagate through the boundary to external space, simulating the actual radiation environment. The simulation results are presented in Figure 10.  
The solid line in Figure 10 depicts the electric field shielding effect shown by the observation points inside the cavity with the opening located at the center of the front plate. We found that, although there were some deviations between the calculation results obtained from theoretical analysis and the actual measured values, they were generally consistent, fully verifying the effectiveness of the method. The simu  
Figure 10: Shielding efficiency curve for rectangular openings.  
Figure 9: Simulation model of single cavity with openings.  
the frequency corresponding to the minimum point of the curve is the resonant frequency; the resonant frequency of the cavity was approximately 0.7 GHz. The TE mode resonant frequency of the cavity was also approximately 0.7 GHz. The shielding effectiveness of the cavity exhibited a negative value at the resonant frequency owing to the resonance of electromagnetic waves inside the cavity.  
Figure 11 shows a comparison of the circular and rectangular openings. Different hole shapes can cause electromagnetic waves to scatter and diffract to different degrees at the hole edges. At 0.5 GHz, the SE value of the circular opening was 14 dB higher than that of the rectangular opening. This is attributed to the sharp edges and corners (such as the right angle of a rectangular hole), which are more prone to strong scattering and diffraction, making it easier for the electromagnetic waves to bypass the shielding body, reducing the shielding effectiveness. In contrast, the edges of the circular holes were smoother, reducing scattering and diffraction, making it more difficult for electromagnetic waves to penetrate the shielding material. The shape of the hole also affected the current distribution on the surface of the shielding body. The long side of the rectangular hole could cross the current path in the shielding body, disrupting the uniformity of the current distribution. This weakens the shielding effect of the eddy current and antimagnetic field of the shielding body, further reducing the shielding effectiveness. Circular holes interfere less with the current distribution; thus, their shielding effectiveness is usually better.