## 3 Results and Discussion
### EMI SE Experimental Characterization  
The sample was placed 30 cm from the transmitter and the receiver to keep the antenna in range. As shown in Figure 2b, the antenna and power supply were connected to a network analyzer, which provided S-parameter plots of the EMI SE of the specimen. The literature [31] and the following parameters, as stated in Equations (1)-(7), have been used to understand the experimental results of EMI SE:  
\[\text{Reflection Coefficient (R)}=|S_{11}|^{2}; \tag{1}\]  
where S\({}_{11}\) = Spectrum parameter in free air medium  
\[\text{Transmission Coefficient (T)}=|S_{12}|^{2}; \tag{2}\]  
where S\({}_{12}\) = Spectrum parameter of bio-based polyurethane foam  
\[\text{Absorption Coefficient (A)}=1-R-T; \tag{3}\]  
\[\text{Shielding Effectiveness Reflection (SE}_{\text{ref}})=-10\text{ log (1-R) [dB]} \tag{4}\]  
\[\text{Shielding Effectiveness Absorption (SE}_{\text{abs}})=-10\text{ log (T/(1-R)) [dB]} \tag{5}\]  
\[\text{Total Shielding Effectiveness (SE}_{\text{total}})=(-10^{*}\text{ log (T) [dB] or SE}_{\text{ref}}+\text{SE}_{\text{abs}}[\text{dB]} \tag{6}\]  
Figure 4: FTIR graph of non-reinforced and nanoparticle-reinforced flexible bio-based polyurethane foam. \[\text{Error Percentage}=(\text{EMI}\,\text{SE}_{\text{Actual}}-\text{EMI}\,\text{SE}_{ \text{Predicted}})/(\text{EMI}\,\text{SE}_{\text{Actual}}) \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Specimen** & \begin{tabular}{c} **Weight of PU Foam** \\ **without** \\ **Reinforcement (g)** \\ \end{tabular} & \begin{tabular}{c} **Graphite** \\ **Nanoplates** \\ **(wt.5)** \\ \end{tabular} & \begin{tabular}{c} **Zirconium** \\ **Oude** \\ **(wt.5)** \\ \end{tabular} & \begin{tabular}{c} **Bamboo** \\ **Charcoal** \\ **(wt.5)** \\ \end{tabular} & \
\begin{tabular}{c} **Weight of PU Foam with Reinforcement** \\ **Theoretical** \\ **Value (g)** \\ \end{tabular} &
\begin{tabular}{c} **Weight Achieved** \\ **after** \\ **Reinforcement (\%)** \\ \end{tabular} & **Density (g/cm\({}^{3}\))** & **EMI (dB)** \\ \hline A0 & 4.217 & - & - & - & - & - & - & 0.015 & 7.71 \\ \hline A1 & 4.137 & 0.4 & 0.4 & 2 & 15.337 & 16.128 & 94.84 & 0.056 & 24.3 \\ \hline A2 & 4.281 & 0.2 & 0.4 & 2 & 14.681 & 15.552 & 94.07 & 0.054 & 24.5 \\ \hline A3 & 4.358 & 0.2 & 0.4 & 1 & 10.758 & 12.069 & 87.81 & 0.042 & 24.2 \\ \hline A4 & 4.330 & 0.4 & 0.4 & 1 & 11.530 & 12.960 & 87.60 & 0.045 & 23.3 \\ \hline A5 & 4.284 & 0.4 & 0.2 & 2 & 14.684 & 15.552 & 94.09 & 0.054 & 23.1 \\ \hline A6 & 4.343 & 0.4 & 0.2 & 1 & 10.743 & 11.808 & 90.09 & 0.041 & 23.8 \\ \hline A7 & 4.305 & 0.2 & 0.2 & 1 & 9.905 & 11.369 & 85.22 & 0.040 & 23.5 \\ \hline A8 & 4.325 & 0.2 & 0.2 & 2 & 13.925 & 15.264 & 90.38 & 0.053 & 23.5 \\ \hline A9 & 4.116 & 0.5 & 0.3 & 1.5 & 13.316 & 14.688 & 89.70 & 0.051 & 24.1 \\ \hline A10 & 4.260 & 0.1 & 0.3 & 1.5 & 11.860 & 12.384 & 95.58 & 0.043 & 24.5 \\ \hline A11 & 4.366 & 0.3 & 0.5 & 1.5 & 13.566 & 14.400 & 93.85 & 0.050 & 23.4 \\ \hline A12 & 4.304 & 0.3 & 0.1 & 1.5 & 11.904 & 12.960 & 91.13 & 0.045 & 24.9 \\ \hline A13 & 4.353 & 0.3 & 0.3 & 2.5 & 16.753 & 16.953 & 98.81 & 0.058 & 25.2 \\ \hline A14 & 4.365 & 0.3 & 0.3 & 0.5 & 8.765 & 10.025 & 85.62 & 0.055 & 23.9 \\ \hline A15 & 4.267 & 0.3 & 0.3 & 1.5 & 12.667 & 12.960 & 97.69 & 0.045 & 23.8 \\ \hline A16 & 4.267 & 0.3 & 0.3 & 1.5 & 12.667 & 12.960 & 97.69 & 0.045 & 23.8 \\ \hline A17 & 4.267 & 0.3 & 0.3 & 1.5 & 12.667 & 12.960 & 97.69 & 0.045 & 23.8 \\ \hline A18 & 4.267 & 0.3 & 0.3 & 1.5 & 12.667 & 12.960 & 97.69 & 0.045 & 23.8 \\ \hline A19 & 4.267 & 0.3 & 0.3 & 1.5 & 12.667 & 12.960 & 97.69 & 0.045 & 23.8 \\ \hline A20 & 4.267 & 0.3 & 0.3 & 1.5 & 12.667 & 12.960 & 97.69 & 0.045 & 23.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Physical properties and EMI results for the experimental design (12). Table 3 indicates the physical properties and EMI results for the experimental designs (L20) with different weight percentages from the RSM central composite design. The weight variation of each polyurethane foam indicates the presence of nanoparticles.