## 2 New EMI Shielding Materials: Biochars, Scaffolds, Rare Earth, and Ferrite-Based Materials
### Rare-Earth-Based Materials as EMI Shielding Material
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Material** & \
\begin{tabular}{c} **Reinforcement and** \\ **Matrix Thickness** \\ \end{tabular} &
\begin{tabular}{c} **EMI Shielding** \\ **Effectiveness** \\ \end{tabular} & **Frequency** & \\ \hline Drywall panels coated with commercial wood biochar & 10 mm & 17 dB & 1 GHz & [47] \\ Cement-based/commercial lignin-derived & 4 mm & 16 dB & 5.4-8 GHz & [48] \\ biochar/PVC composite & \(\sim\)8 mm & \(>\)32 dB & 8–12 GHz & [36] \\ EBC@CNF@MVCNT composite & 0.1–0.5 mm & 39 dB & 1–3 GHz & [49] \\ Diocarb/polytetrafluoroethylene composite & 0.2 mm & 15.5 dB & 8–12 GHz & [50] \\ Apple and quinone biowaste-based biochars & 0.15 mm & 26.5 dB & 8–12 GHz & [37] \\ _Ricinus communis_ outer shell-based & 0.15 mm & 26.5 dB & 8–12 GHz & [37] \\ biodcarb/epoxy composite & 4 mm & 15 dB & 10 GHz & [57] \\
18 wt.% lignin-based biochar/cementitious composite & 4 mm & 15 dB & 10 GHz & [58] \\ Cashew shell biochar/carbon fiber-reinforced epoxy & not reported & –48.6 dB & 18 GHz & [58] \\ resin composite & & 31.5 dB & 8 GHz & \\ Jackfruit rag biochar/waste silk fiber-reinforced vinyl & not reported & 47.25 dB & 12 GHz & [59] \\ ester composite & & 63 dB & 16 GHz & \\  & & 68.25 dB & 18 GHz & \\ Cellulose scaffold/AgNP composite & 1 mm & 69.1 dB & 8.2–12.4 GHz & [52] \\ Carbon scaffold/polyurethane/Fe\({}_{3}\)O\({}_{4}\) NP composite & –8 mm & 32 dB & 8.2–12.4 GHz & [53] \\ Cellulose-paper-based scaffold/Fe\({}_{3}\)O\({}_{4}\) NP composite & 1.3 mm & 1805.9 dB/cm\({}^{2}\) g & 10.3 GHz & [54] \\
3D cellulose scaffold/CNT/MXene composite & 0.25 mm & 29.3 dB & 18–26.5 GHz & [55] \\ Hybrid scaffold coupled with high-quality graphene & 6 mm & 72.86 dB & 8.2–12.4 GHz & [56] \\ array/MXene-Co aerogel & 10 mm & 35.9 dB & 8.2–12.4 GHz & [51] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._tion control the morphology [67]. With a lowered concentration, the resulting nanoparticles exhibited a spherical morphology but gradually changed to flower-shaped with increasing concentration. Pure MoS2 has a relatively homogeneous loss mechanism, limited impedance matching, and a limited ability to absorb EW. Doping is an effective method to improve the electromagnetic properties of materials [68]. For instance, palladium-doped few-layer MoS2 nanosheets grown on the surface of multi-walled CNTs and the 10% Pd nanohybrid possess a higher EMI shielding effectiveness (SE \(\sim\)26.50 dB) than that of SE \(\sim\)21.55 dB in the undoped MoS2/CNT at the same thickness of 1 mm [69]. Laser-cladded novel FeCo-based alloys with different RROs, such as La2O3, Y2O3, Nd2O3, and Gd, possess enhanced electromagnetic shielding performance with a shielding effectiveness (SE) of up to \(\sim\)96 dB at 23.9 GHz and an ability to absorb 99.9999% of EMWs [70; 71]. [PERSON] et al. [72] discovered that REE substitution in Fe4N could modulate magnetic moments and magnetic exchange coupling interactions and the change in spin polarizability. [PERSON] et al. [73] studied the microwave absorption properties of high-entropy hexaborides containing rare earth, including Ce, Y, Sm, Er, and Yb, prepared by a boron carbide reduction reaction, which showed good absorption properties with an effective bandwidth of 4.3 GHz, while [PERSON] et al. [74] studied the absorption properties of high-entropy rare earth silicide carbides and high-entropy rare earth oxides based on different ratios of Tm, Y, Dy, Gd, Tb, Pr, and Tb ions, prepared by a solid-state reaction method, which showed good absorption properties with an effective bandwidth of 4.5 GHz. Absorbent, magnetic cores made of alloys based on Fe and Nb are suitable for EMI reduction signals with a 6-7 MHz frequency. However, [PERSON] et al. constructed a broadband coaxial probe head allowing the measurement of Fe-based nanocrystalline cores containing Nb up to 1 GHz using a reflectometry method with a vector network analyzer (VNA) [75].