## 3 Results and Discussion
### EMI SE Experimental Characterization
The percentage of weight achieved after reinforcement using absorption and the hydrothermal process is shown in Table 3. As shown in Table 3, with a GNP weight percentage of 0.3, ZrO2 weight percentage of 0.3, and BC weight percentage of 2.5, specimen A13 exhibits the highest maximum EMI value of 25.2 dB. The EMI SE of nanocomposites is affected by morphology, GNP, ZrO2 and BC loading, incident radiation frequency, matrix composition, and nanocomposite thickness. Table 4 depicts the EMI shielding effectiveness, which is SEtotal, of various nanocomposites over the frequency ranges of 8-12 GHz, derived using Equations(1)-(6), as well as the parameters obtained using Equations (1)-(4) for the free air medium shown in Table 5. Due to the limit of the measurement equipment, we only analyzed the effective contribution of different attenuating mechanisms in the X-band frequency range. Table 4 shows that in the frequency range of 8-12 GHz, the experimental specimen A13 has the highest EMI shielding effectiveness of \(-\)25.62 dB to \(-\)28.03 dB. Based on these findings, we concluded that the EMI SE of nanoparticle-reinforced PU foam has improved, comparing specimen A without nanoparticles, which has an EMI shielding effectiveness ranging from \(-\)8.66 dB to \(-\)17.75 dB. The shielding effectiveness value's pessimistic sign denotes the breakdown of the electromagnetic wave power to the incident electromagnetic wave. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Specimen**} & **Transmission Coefficient** & **Absorption Coefficient** & **Shielding Effectiveness Absorption (SEabs) (dB)** & **Total Electromagnetic Shielding Effectiveness (EMISEtotal) (dB)** \\ \hline A0 & 7.34–59.57 & \(-\)9.07\(\sim\)\(-\)78.82 & \(-\)6.28\(\sim\)\(-\)4.91 & \(-\)8.66\(\sim\)\(-\)17.75 \\ \hline A1 & 364.81–590.49 & \(-\)366.54\(\sim\)\(-\)609.74 & \(-\)23.24\(\sim\)\(-\)14.87 & \(-\)25.62\(\sim\)\(-\)27.71 \\ \hline A2 & 372.49–600.25 & \(-\)374.22\(\sim\)\(-\)619.5 & \(-\)23.33\(\sim\)\(-\)14.94 & \(-\)25.71\(\sim\)\(-\)27.78 \\ \hline A3 & 372.49–585.64 & \(-\)374.22\(\sim\)\(-\)604.89 & \(-\)23.33\(\sim\)\(-\)14.83 & \(-\)25.71\(\sim\)\(-\)27.68 \\ \hline A4 & 345.96–542.89 & \(-\)347.69\(\sim\)\(-\)562.14 & \(-\)23.01\(\sim\)\(-\)14.50 & \(-\)25.39\(\sim\)\(-\)27.35 \\ \hline A5 & 345.96–533.61 & \(-\)347.69\(\sim\)\(-\)552.86 & \(-\)23.01\(\sim\)\(-\)14.43 & \(-\)25.39\(\sim\)\(-\)27.27 \\ \hline A6 & 364.81–566.44 & \(-\)366.54\(\sim\)\(-\)585.69 & \(-\)23.24\(\sim\)\(-\)14.69 & \(-\)25.62\(\sim\)\(-\)27.53 \\ \hline A7 & 349.69–552.25 & \(-\)351.42\(\sim\)\(-\)571.5 & \(-\)23.06\(\sim\)\(-\)14.58 & \(-\)25.44\(\sim\)\(-\)27.42 \\ \hline A8 & 334.89–552.25 & \(-\)336.62\(\sim\)\(-\)571.5 & \(-\)22.87\(\sim\)\(-\)14.58 & \(-\)25.25\(\sim\)\(-\)27.42 \\ \hline A9 & 376.36–580.81 & \(-\)378.09\(\sim\)\(-\)600.06 & \(-\)23.38\(\sim\)\(-\)14.80 & \(-\)25.76\(\sim\)\(-\)27.64 \\ \hline A10 & 392.04–600.25 & \(-\)393.77\(\sim\)\(-\)619.5 & \(-\)23.55\(\sim\)\(-\)14.94 & \(-\)25.93\(\sim\)\(-\)27.78 \\ \hline A11 & 345.96–547.56 & \(-\)347.69\(\sim\)\(-\)566.81 & \(-\)23.01\(\sim\)\(-\)14.54 & \(-\)25.39\(\sim\)\(-\)27.38 \\ \hline A12 & 388.09–620.01 & \(-\)389.82\(\sim\)\(-\)639.26 & \(-\)23.51\(\sim\)\(-\)15.08 & \(-\)25.89\(\sim\)\(-\)27.92 \\ \hline A13 & 364.81–635.04 & \(-\)366.54\(\sim\)\(-\)654.29 & \(-\)23.24\(\sim\)\(-\)15.18 & \(-\)25.62\(\sim\)\(-\)28.03 \\ \hline A14 & 357.21–571.21 & \(-\)358.94\(\sim\)\(-\)590.46 & \(-\)23.15\(\sim\)\(-\)14.72 & \(-\)25.53\(\sim\)\(-\)27.57 \\ \hline A15 & 372.49–566.44 & \(-\)374.22\(\sim\)\(-\)585.69 & \(-\)23.33\(\sim\)\(-\)14.69 & \(-\)25.71\(\sim\)\(-\)27.53 \\ \hline A16 & 372.49–566.44 & \(-\)374.22\(\sim\)\(-\)585.69 & \(-\)23.33\(\sim\)\(-\)14.69 & \(-\)25.71\(\sim\)\(-\)27.53 \\ \hline A17 & 372.49–566.44 & \(-\)374.22\(\sim\)\(-\)585.69 & \(-\)23.33\(\sim\)\(-\)14.69 & \(-\)25.71\(\sim\)\(-\)27.53 \\ \hline A18 & 372.49