Research progress on high-performance electromagnetic interference shielding materials with well-organized multilayered structures

With the rapid advancement of wireless electronics and the widespread integration of electronic devices into daily life, the radiation pollution of electromagnetic waves (EMWs) has become an undeniable concern, leading to the rapid development of high-performance electromagnetic interference (EMI) shielding materials. Different from the traditional uniform structure, the construction strategies of multilayered structures with multiple interfaces have been proven to effectively enhance the shielding effectiveness and absorption loss of EMI shielding materials. In this review article, a preliminary analysis of EMI shielding and EMWs attenuation mechanisms was initially conducted. The common EMI shielding materials, including metallic materials, carbon-based materials, magnetic materials, two-dimensional transition metal carbonitrides, and conductive polymer composites, were then introduced. The particular structures of EMI shielding materials with multiple interfaces, encompassing porous structure, segregated structure, preconstructed structure, and multilayered structure, were comprehensively summarized. It was emphasized that the multilayered structures offered various advantages, including the presence of abundant multiple interfacial reflections and polarizations, optimal impedance matching capabilities, flexible designability, and controllable distribution of hybrid conductive/magnetic fillers. The focus of this paper mainly lies in the evaluation of the EMI shielding performance of shielding materials with multilayered structures. A comprehensive overview was presented enumerating the preparation processes for EMI shielding materials with multilayered structures, including techniques such as vacuum-assisted filtration, layer-by-layer casting and assembly, three-dimensional printing, and polymer-assisted methods. The multilayered structures were primarily categorized into the following types: sandwich-like layered structures (symmetrical and asymmetrical), randomly multilayered structures, regularly alternating multilayered structures, gradient distribution structures, as well as mimicking "brick and mortar" structures of shell pearls. Finally, the challenges faced by EMI shielding materials with multilayered structures were summarized, and the prospects for their future development were discussed.