## 5 Conclusions  
The concise conclusions of this study are as follows:  
1. The study effectively developed and optimized electromagnetic wave-absorbing materials (EMAMs) using multi-layer PP/GNP and PP/MWCNT nanocomposites adapted for X-band applications.
2. The optimization approach, performed using NSGA-II and validated with PSO, identified a high-performance two-layer structure consisting of 1.5% MWCNT/PP/epoxy and 2.7% GNP/PP/epoxy, achieving a reflection loss of \(-21\) dB at a 4.2 GHz bandwidth.
3. The work emphasizes the vital significance of additive manufacturing in providing accurate material functioning and structural integration, which are required for broadband absorption.
4. The synergy between MWCNTs and GNPs in multi-layer nanocomposites indicates their ability to improve EMAM performance, making them suitable candidates for aircraft, radar systems, and electronic communication equipment.
5. Prospects of PP/GNP and PP/MWCNT materials include the following: 1. The lightweight and flexible features of the PP/GNP and PP/MWCNT nanocomposites and their superior electromagnetic properties make them promising for future applications in portable electronic devices, 5G communication systems, and stealth technologies. 2. Their scalability using additive manufacturing processes allows for mass production and widespread application in sophisticated industries. 3. Further research can look into expanding their operating frequency range to accommodate larger applications in millimeter-wave technology and next-generation communication systems.
6. Using modern optimization algorithms such as NSGA-II and PSO in material design demonstrates a viable path towards efficient and cost-effective solutions in electromagnetic wave absorption.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/jcs8120537/s1](https://www.mdpi.com/article/10.3390/jcs8120537/s1)]([https://www.mdpi.com/article/10.3390/jcs8120537/s1](https://www.mdpi.com/article/10.3390/jcs8120537/s1)), Figure S1: TGA analysis of PP, GNP/PP Composite.  
This research was funded by Deanship of Research and Graduate Studies at King Khalid University grant number RGP2/386/45 and the APC was funded by Deanship of Research and Graduate Studies at King Khalid University.  
The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding author.  
The author extends their appreciation to the Deanship of Research and Graduate Studies at King Khalid University for funding this work through the Large Research Project under grant number RGP2/386/45.  
The author declares no conflicts of interest.  
\begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**S.No** & **Nanocomposite** & **No.of Layers** & **Structure Thickness** & **RL (X-Band)** & **Ref** \\ \hline
1. & Graphite, CNF, Epoxy & 3 & 9 mm & \(-10\) dB & [42] \\
2. & MWCNT, Epoxy & 3 & 12.9 mm & \(-10\) dB & [43] \\
3. & MWCNT, Epoxy (variable incident angle) & 6 & 18 mm & \(-12\) dB & [44] \\
4. & 1.5\% MWCNT/PP/epoxy \& & 2 & 5.52 mm & \(-21\) dB & Present \\  & 2.7\% GNP/PP/epoxy & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: RL comparison with the literature.