## 2 New EMI Shielding Materials: Biochars, Scaffolds, Rare Earth, and Ferrite-Based Materials
### Scaffolds as EMI Shielding Material  
Many structural patterns, including highly porous materials and conductive structures such as multilayer composites obtained by stacking cellulose nanofibers/reduced graphene oxide (rGO), rGO films, and multistage composite foams, are recognized as excellent EMI shielding materials. These structures are obtained using vacuum-assisted filtration, freeze-drying techniques, or electroless deposition [51]. The mentioned procedures allow for a reduction in the reflection coefficient, but they are complex and often not reliable. The innovative manufacturing technologies imply 3D network structures (scaffolds) that can be decorated with metal nanoparticles [52], coated by polymers, encapsulated with paraffin [53], etc. These approaches enable design freedom, flexibility, precise control over the shape and size, and the connectivity of porous structures. Cellulose scaffolds (CSs) are recognized as a promising material for EMI shielding applications due to the ability of cellulose nanofibers to improve the thermal and mechanical features of nanocomposites. [PERSON] et al. represented a 3D network structure of cellulose scaffolds decorated with silver nanoparticles (AgNPs) [52]. The scaffolds were filtered at the epoxy matrix and cured at 40 \({}^{\circ}\)C to fix the nanoparticles. The obtained composite possesses a thermal conductivity of 2.52 W/m/K, which is over 11-fold the thermal conductivity of pure epoxy. The extremely high electrical conductivity of 53.691 S/m caused a remarkable SE value of 69.1 dB. [PERSON] et al. designed a scaffold connected with metal nanoparticles [53]. In this work, the shape-stable composite was composed of a paraffin impregnated in a biological porous carbon scaffold, followed by a coating with polyurethane and Fe\({}_{3}\)O\({}_{4}\) nanoparticles. The biological porous carbon was obtained from a loofah sponge by immersion in a phenolic resin solution followed by carbonization. Scanning electron microscopy (SEM) results revealed that the system kept its original shape with a 3D and honeycomb-like porous structure of single fibers after carbonization. The polyurethane coating provided adequate mechanical support and effective leak-proof performance. The produced framework shows strong EMI shielding performance (up to 32 dB). Another study based on the encapsulation of Fe\({}_{3}\)O\({}_{4}\) nanoparticles in carbon scaffolds was conducted by [PERSON] et al. [54]. Herein, laminar cellulose-paper-based scaffolds with bidirectional gradient distributed Fe\({}_{3}\)O\({}_{4}\) nanoparticles were constructed via immersion, drying, and carbonization processes. The resulting carbon scaffolds exhibited high in-plane electrical conductivity (96.3 S/m) and high shielding efficiency (1805.9 dB/cm\({}^{2}\)g). A 3D cellulose scaffold was combined with a CNT/MXene composite [55]. Nanosheets of the composite were inserted into a cellulose scaffold by vacuum impregnation. Finally, a hydrophobic and multifunctional 3D system was produced by wrapping it with poly (dimethylsiloxane). The composite had a high compressive strength of 1.53 MPa, a maximum strain at fracture of 74.1%, and an outstanding SE (29.3 dB). [PERSON] et al. reported a dual-ice templating assembly strategy to prepare a dual-interpenetrated scaffold [56]. The scaffold was linked with a high-quality graphene array and porous MXene-Co aerogel. It showed an absorption-dominated EMI SE of 72.86 dB. Three-dimensional-printing technology was applied for scaffold fabrication based on a triply periodic minimal surface and 70% porosity [42]. The monolithic layered dipping method was used to regulate the gradient distribution of carbon nanotubes on the 3D-printed scaffold surface and ensure integrity. This system blocked 99.9% of EM waves. The value of the SE in this case was 35.9 dB. Previous research showed that scaffolds are new-generation, easy-to-manufacture materials with excellent EMI shielding performance.