## 5 Enclosure Radiation Interference Prediction Using Equivalent Model  
In practical applications, multiple axial flow fans are employed to dissipate heat from components inside the enclosure of electronic equipment. As shown in Figure 18, the enclosure features apertures on its rear and sides, and two axial fans are installed inside the enclosure via a metal plate. These fans create high-speed airflow at the rear of the enclosure, which passes through the apertures to provide air-cooling and facilitate the dissipation of heat generated by the electronic equipment within the enclosure.  
The dimension of the electronic enclosure is 600 mm \(\times\) 300 mm \(\times\) 900 mm. The equivalent source containing the fan is calculated independently, with a distance of 50 mm from the fan as the equivalent surface. A comparison of the electric field distribution inside the enclosure is depicted in Figure 19.  
According to the calculation results, the axial fan inside the enclosure generates radiated interference externally. The electric field distribution inside the enclosure, as determined by both models, shows significant consistency. Discrepancies exist in the electric field distribution near the fan installation position because the equivalent model only contains electromagnetic field data on the surface of the closed domain from internal radiation sources. The internal electric field distribution results in the equivalent model are derived by extrapolating the surface electromagnetic field inward, which may be  
Figure 19: Comparison of electric field distribution inside an electronic enclosure in top view. (**a**) Calculated by detailed model; (**b**) calculated by equivalent model.  
\begin{table}
\begin{tabular}{l c c c} \hline  & \(\mathbf{ADM_{tot}}\) & \(\mathbf{FDM_{tot}}\) & \(\mathbf{GDM_{tot}}\) \\ \hline Evaluation of the two models & 0.0814/very good & 0.3695/good & 0.3971/good \\ Evaluation of equivalent model & 0.1165/very good & 0.4920/fair & 0.5354/fair \\ and measurements & & & \\ \hline \end{tabular}
\end{table}
Table 3: FSV evaluation of computational models and measurements.  
Figure 18: Axial flow fan installed inside the enclosure.  
influenced by other interference sources and cannot accurately represent the actual internal field distribution of the field source. In the external domain surrounding the equivalent surface, the outward electromagnetic radiation from both models is considered equivalent.  
An electric field probe is set inside the aperture at the rear side of the enclosure. The curve of the electric field strength with frequency is shown in Figure 20, and it is obvious that the electromagnetic energy leaks outward through the aperture of the enclosure. The evaluation results are shown in Table 4. The FSV results also illustrate the consistency between the equivalent model and the detailed model.  
Table 5 presents a comparison of the grid parameters and computation time for the two computational models. The equivalent model leads to an 81.4% reduction in computation time. Notably, the equivalent model only requires a single calculation of the interference source to determine the electromagnetic field and can be used repeatedly, while the detailed model necessitates multiple iterations of the field circuit for each interference source. Thus, the equivalent model offers improved computational efficiency for analyzing radiation emissions from multiple interference sources.