## 3 Results and Discussion
### EMI Shielding of BP/CFRP Hybrid Composites  
This study examines the effect of BP placement and relative CFRP ply orientation to understand the EMI SE of hybrid composites. All the specimen configurations used for the study are detailed in Table 4. Initially, the BP position is varied within a simple [90,0] baseline configuration to understand the effect of BP placement. Subsequently, to assess the influence of adjacent ply orientation, BP is introduced between two plies and one of the ply orientations is modified. Finally, the effects of BP in a composite with a [90, 0, \(\pm\)45, 0, 90]\({}_{8}\) stacking sequence are investigated. The total SE, along with its reflection and absorption components for a single BP film and a [90,0] baseline laminate, are shown in Figures 16a and 16b, respectively. These results show good agreement with the available literature [38; 39; 40]. At 2 GHz, the total shielding effectiveness (SE) for the BP is predicted to be approximately 43 dB, which aligns with the manufacturer's reported value of 40 dB [32]. Additionally, the total EMI SE for a [90,0] laminate with a thickness of 0.5 mm in the X-band (8 GHz to 12 GHz) is predicted to range from 62 dB to 57 dB, which is consistent with the experimental data reported in the literature. A dominant absorption effect was observed in the shielding effectiveness of the [90,0] laminate when contrasted with the BP film, owing to its thickness. It was observed that the presence of BP significantly enhances the overall SE of a composite. Particularly at frequencies exceeding 1 GHz, wherein the electrical conductivity of CFRP experiences a significant decline, the corresponding EMI SE also drops. The incorporation of BP interleaf proves effective in sustaining elevated electrical conductivity, even at higher frequencies, thereby preventing a reduction in the overall shielding effectiveness. The effect of BP location within the baseline [90,0] laminate is depicted in Figure 16c-e. By varying the position of BP within the composite, the SE also varies slightly. It was inferred that due to the complex reflection and absorption shielding mechanisms, the stacking sequence of the hybrid BP/CFRP composites greatly influences the overall shielding effectiveness. Figure 17 illustrates the effect of ply orientations adjacent to the BP on its EMI SE. Optimal shielding against undesired radiation is attained by integrating two unidirectional plies with the greatest variation in orientation angles. The inclusion of more uniformly oriented plies aids in transitioning towards a quasi-isotropic laminate, resulting in a notable decrease in the anisotropy of electrical conductivity and enhancing the overall SE. Moreover, the isotropic nature of BP further enhances the EMI shielding performance by reducing the anisotropy in electrical properties. In the case of thicker balanced symmetric laminates, as the frequency increases, the effect of BP is more pronounced due to the drop in the CFRP conductivity. The use of BP interleaves can help significantly improve the EMI SE of thick CFRP laminates. This behavior can be observed in Figure 18, which shows the EMI SE of a 12-ply sample with and without the BP. \begin{table}
\begin{tabular}{c c} \hline \hline
**Label** & **Configuration** \\ \hline Case 1 & [90, 0] \\ (BP Placement) & [BP, 90, 0] \\  & [90, BP, 0] \\ \hline Case 2 & [0, BP, 0] \\ (Adjacent Ply) & [45, BP, 0] \\  & [90, BP, 0] \\ \hline Case 3 & [90, 0, \(\pm\) 45, 0, 90]\({}_{8}\) \\ (Standard Configuration) & [90, 0, BP, \(\pm\) 45, 0, 90]\({}_{8}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Specimen configuration. Finally, the shielding effectiveness of BP is compared to other techniques, such as incorporating copper mesh [24]. Figure 19 illustrates that the EMI shielding effectiveness of BP composites remains significantly high beyond 1 GHz. This is credited to the increased electrical conductivity of the BP layer at high frequencies, in contrast to copper, which experiences a gradual decline in conductivity with frequency due to the skin effect.