## 12 Porous Polyimide Nanocomposites for Electromagnetic Interference Shielding
These carbon foams had a density of 0.091 g.cm\({}^{-3}\) and showed a superior EMI SE value of \(\sim\)54 dB and specific EMI SE of 593.4 dB-cm\({}^{3}\)/g, respectively, at 10 GHz and at a thickness of 2.0 mm [117]. It is also worth mentioning that no conductive nanofillers were used during the fabrication of carbon foams. Numerous porous nanocomposite foams and aerogels have been comprehensively studied for their microwave absorption performance and EMI shielding ability. Table 2 summarizes the EMI shielding properties (SETotal, SSE), electrical conductivity, thickness, density and test frequency range of some porous nanocomposites studied in the literature. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Sr No.** & \begin{tabular}{c} **Aerogel/Foam** \\ **Composition** \\ \end{tabular} & \begin{tabular}{c} **Measurement** \\ **Technique** \\ \end{tabular} & \begin{tabular}{c} **Thickness** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Density** \\ **(g/cm\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Frequency (GHz)** \\ **(g/cm)** \\ \end{tabular} & \begin{tabular}{c} **Eletical** \\ **Conductivity** \\ **(S/m)** \\ \end{tabular} & \
\begin{tabular}{c} **SE\({}_{\text{Total}}\)** \\ **(dB)** \\ \end{tabular} &
\begin{tabular}{c} **Specific** \\ **EMI SE** \\ **(dB.g\({}^{-1}\)cm\({}^{3}\))** \\ \end{tabular} & **Ref** \\ \hline
1 & CNT sponge & waveguide & 1.8 & 10.0 & 8–12 & 150–300 & 54.8 & 5480 & [118] \\ \hline
2 & CNT/PDMS & waveguide & 2.0 & & 8–12 & 150–300 & 46.3 & - & [118] \\ \hline
3 &
\begin{tabular}{c} rGO/epoxy \\ composite \\ \end{tabular} & - & \(>\)0.1 & & & \(-\)0.01 & 38 & 35.3 & [119] \\ \hline
4 & PEI/GP/FeO4 foam & - & & 0.28–0.4 & 8–12 & & \(-\)41.5 & - & [120] \\ \hline
5 & GAF & coaxial & 1.4 & 0.06 & 0.1–3 & \(2.5\times 105\) & \(-\)138 & - & [121] \\ \hline
6 & GAF & coaxial & 0.12 & 0.41 & 2–18 & 6600 & 70–105 & - & [121] \\ \hline
7 & GAs & waveguide & 4 & 0.43 & 8–12 & 4.32 & 30 & - & [122] \\ \hline
8 & Ni-NiO/NCA & - & 1.5 & 0.42 & 15.2 & & \(-\)41.9 & - & [123] \\ \hline
9 & carbon/Fe3O4@Fe & - & 2 & 13–18 & & \(-\)49.6 & - & [124] \\ \hline
10 & CNT sponge & coaxial & 2–3.5 & 0.02 & 1–18 & 278 & 20 & 1100 & [125] \\ \hline
11 & CNT/Epoxy & - & 5–10 & 5 & 8–12 & 516 & 33 & - & [126] \\ \hline
12 & RGO/LDC Aerogel & waveguide & 2 & 8.0 & 8.2–12.4 & - & 49.2 & 53,250 & [127] \\ \hline
13 & RGO/LDC Aerogel & waveguide & 2 & 2.0 & 8.2–12.4 & - & 21.3 & 10,650 & [127] \\ \hline
14 & Graphene Aerogel & - & 3 & 7.6 & 14.6 & - & 30.53 & - & [128] \\ \hline
15 & CF@G@PPy aerogels & - & 3 & 8.8 & 9–12.6 & - & 40.59 & - & [128] \\ \hline
16 & GA-CT & - & 2 & 0.07 & - & - & 27 & 371–385 & [129] \\ \hline
17 & GA-CT & - & 3 & 0.07 & - & - & 37 & 514–528 & [129] \\ \hline
18 & CNTs/GNS@CoFe2O4 & waveguide & 3.0 & 0.095 & 8.2–12.4 & - & 29.1 & - & [130] \\ \hline
19 & epoxy/TGA & - & 4 & & 8–12 & - & 27 & - & [7] \\ \hline
20 & epoxy/TAGA (axial) & - & 4 & & 8–12 & 980 & 25 & - & [7] \\ \hline
21 & epoxy/TAGA (radial & - & 4 & & 8–12 & 96 & 32 & - & [7] \\ \hline
22 & Epoxy/PGAs & Coaxial & 4 & 4.0 & 8–12 & 73 & 35 & & [131] \\ \hline
23 & RGO/Ti3C2 TX foam & waveguide & 3.22 & 0.0033 & 8.2–12.4 & - & & 14,299.2 & [132] \\ \hline
24 & MXene aerogels & Waveguide & 4 & 0.004 & 8.2–12.4 & 22 & 75 & 990 & [133] \\ \hline
25 & Ti3C2 TX MXene/ & Coaxial & 2 & 0.31 & 11.2 & - & \(-\)43.4 & - & [121] \\ \hline
26 & MXene Foams & - & 3.2 & & & 58 00 & \(\approx\)70 & - & [134] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Measurement technique, shield thickness (mm), frequency (GHz), electrical conductivity (S/m), SE\({}_{\text{Total}}\) (dB) and specific EMI SE (dB.g\({}^{-1}\).cm\({}^{3}\)) of some porous nanocomposites reported in the literature. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sr No. **} & **Aerogel/Foam** & **Measurement** & **Thickness** & **Density** & **Frequency (GHz)** & **Electrical** & \multirow{2}{*}{ \begin{tabular}{c} SE\({}_{\text{Total}}\) \\ **(g/cm\({}^{3}\))** \\ \end{tabular}