## 2 New EMI Shielding Materials: Biochars, Scaffolds, Rare Earth, and Ferrite-Based Materials
### Iron Oxide-Based Materials as EMI Shielding Material
The porous nanocomposite that resulted from loading 7 wt.% graphene nanoplatelets and 7 wt.% Fe\({}_{3}\)O\({}_{4}\) nanoparticles showed a satisfactory specific electromagnetic interference (EMI) shielding effectiveness of about 37.03 dB/(g/cm\({}^{3}\)), which was much higher than that of the solid equivalents (28.30 dB/(g/cm\({}^{3}\))). In another study, Fe\({}_{3}\)O\({}_{4}\)/thermally annealed graphene aerogel (Fe\({}_{3}\)O\({}_{4}\)/TAGA) was created by first thermally annealing ethylenediamine-functionalized Fe\({}_{3}\)O\({}_{4}\) (NH\({}_{2}\)-Fe\({}_{3}\)O\({}_{4}\)) nanoparticles with graphene oxide (GO), followed by the addition of l-ascorbic acid [128]. Then, the Fe\({}_{3}\)O\({}_{4}\)/TAGA/epoxy nanocomposites were created using a template-casting technique. The resulting Fe\({}_{3}\)O\({}_{4}\)/TAGA/epoxy nanocomposites achieved the highest electromagnetic interference shielding effectiveness (EMI SE of 35 dB in the X-band) when the mass ratio of GO to NH\({}_{2}\)-Fe\({}_{3}\)O\({}_{4}\) was 2:1 and the total mass fraction of Fe\({}_{3}\)O\({}_{4}\)/TAGA was 2.7 wt.% (comprising 1.5/1.2 wt.% Fe\({}_{3}\)O\({}_{4}\)/TAGA). This was significantly better than epoxy nanocomposites with the same Fe\({}_{3}\)O\({}_{4}\)/thermally annealed graphene oxide (Fe\({}_{3}\)O\({}_{4}\)/TAGO) loading, which only showed an EMI SE of 10 dB. [PERSON] et al. created magnetic reduced graphene oxide rGO@Fe\({}_{3}\)O\({}_{4}\) nanoplatelets (NPs), which were used as fillers, by co-precipitation and electrostatic self-assembly [129]. The nanocomposites were made by applying external magnetic fields to align rGO@Fe\({}_{3}\)O\({}_{4}\) NPs during epoxy curing. Because of the anisotropic properties of rGO@Fe\({}_{3}\)O\({}_{4}\) NPs and external magnetic fields, the nanocomposite containing aligned rGO@Fe\({}_{3}\)O\({}_{4}\) NPs showed anisotropic thermal conductivity. The produced sample exhibited exceptional thermal stability and 13.45 dB EMI shielding at 8.2 GHz. Overall, the rGO@Fe\({}_{3}\)O\({}_{4}\) NPs' in-plane interaction was enhanced by aligning them under a magnetic field, which promoted the growth of horizontal thermal conductive networks. Reflection is the main EMI shielding mechanism. Three-dimensional Fe\({}_{3}\)O\({}_{4}\)-decorated carbon nanotube/reduced graphene oxide foam/epoxy (3D Fe\({}_{3}\)O\({}_{4}\)-CNT/rGF/EP) nanocomposites with highly aligned three-dimensional structures were created by [PERSON] et al. using a simple template approach [130]. The obtained 3D Fe\({}_{3}\)O\({}_{4}\)-CNT/rGF/EP nanocomposites with 0.24 wt.% rGF and 2.76 wt.% Fe\({}_{3}\)O\({}_{4}\)-CNTs showed a remarkable electrical conductivity of 15.3 S/m and an EMI SE of 36 dB within the X-band range, which was a nearly 482% improvement when compared to the EMI SE value of physically blended Fe\({}_{3}\)O\({}_{4}\)-CNT/EP nanocomposites without a three-dimensional structure (~6 dB). Using a supercritical carbon dioxide (Sc-CO\({}_{2}\)) foaming technique, lightweight and flexible methyl vinyl silicone rubber (VMQ)/multi-walled carbon nanotube (MWCNT)/ferriferrous oxide (Fe\({}_{3}\)O\({}_{4}\)) nanocomposite foams with superior EMI shielding capabilities were created [131]. The addition of a cellular structure and magnetic Fe\({}_{3}\)O\({}_{4}\) nanoparticles greatly improved the VMQ/MWCNT/Fe\({}_{3}\)O\({}_{4}\) foams' microwave-absorbing capacity by successfully lowering secondary electromagnetic wave interference brought on by reflection. In the 8.2-12.4 GHz frequency range, these nanocomposite foams, which have an approximate density of 0.48 g/cm\({}^{3}\), showed an EMI shielding efficiency (SE) of 27.5 dB and an average absorption ratio of up to 64%. The foams had a specific EMI SE of about 72 dB g\({}^{-1}\) cm\({}^{3}\) and a high conductivity of about 14.6 S/m with a filler loading of 1.78 vol.%. [PERSON] et al. [132] used rice-husk-based activated carbon (AC) and produced composites with acicular or octahedral Fe\({}_{3}\)O\({}_{4}\) nanoparticles.