With rapid development of 5G communication technologies, electromagnetic interference (EMI) shielding for electronic devices has become an urgent demand in recent years, where the development of corresponding EMI shielding materials against detrimental electromagnetic radiation plays an essential role. Meanwhile, the EMI shielding materials with high flexibility and functional integrity are highly demanded for emerging shielding applications. Hitherto, a variety of flexible EMI shielding materials with lightweight and multifunctionalities have been developed. In this review, we not only introduce the recent development of flexible EMI shielding materials, but also elaborate the EMI shielding mechanisms and the index for "green EMI shielding" performance. In addition, the construction strategies for sophisticated multifunctionalities of flexible shielding materials are summarized. Finally, we propose several possible research directions for flexible EMI shielding materials in near future, which could be inspirational to the fast-growing next-generation flexible electronic devices with reliable and multipurpose protections as offered by EMI shielding materials.

Vigorous development of 5G communication technologies can boost mobile networks yet bring in electromagnetic interferences and safety concerns in utilizing electronic devices. Particularly, 5G network can not only involve a low‐frequency band of n78 (3.3–3.8 GHz) but also cover multi‐frequency bands of n77 (3.3–4.2 GHz) and n79 (4.4–5.0 GHz), displaying multiple electromagnetic radiations. Countless efforts have been devoted to investigating electromagnetic wave (EMW) absorbers with low‐ and multi‐band absorption properties. However, in terms of emerging materials and designs, few reports propose the mechanisms related to those properties. This perspective briefly reviews the impressive achievements of low‐ and multi‐frequency EMW absorbers and analyzes the design strategies that may enable low‐ and multi‐frequency absorption. Furthermore, the cutting‐edge mechanisms of corresponding electromagnetic responses, such as Snoek limit, quarter wavelength, and dielectric‐magnetic synergy effects are elaborated. Thus, this perspective can shed light on the new trends and ongoing challenges for EMW absorbers and further promote their practical application.

Multiple relaxation behaviors are promising for broad frequency band and strong electromagnetic wave (EMW) absorption based on polarization‐controlled electromagnetic (EM) attenuation. However, rational selection of materials and structure manipulation through tunable substitution or phase control are challenging toward optimization of EMW absorption. Herein, bi‐metallic organic frameworks (B‐MOFs) with various morphologies are employed as EMW absorbers. Remarkably, the polar units can be enhanced by introducing Ni‐metal nodes into the Cu‐coordinated MOFs, rendering the B‐MOFs with self‐polarized properties and consecutive multifrequency EMW absorption behaviors. The maximum reflection loss of acetylene black (ACET) filled NiCu‐MOFs can reach –40.54 dB together with a wide bandwidth (<‐10 dB) of 5.87 GHz at a thickness of 2.5 mm. As a counterpart of the Ni/Cu/C derivatives, significantly increased broad band absorption (6.93 GHz) and multifrequency absorbing and polarization characteristics are also maintained in bimetal coexisting carbonized architectures as prepared by calcination of CuNi‐MOFs. This work demonstrates that the performance of effective absorbing frequency band can be enhanced in multi‐metallic organic frameworks‐based architectures, and paves a novel avenue for developing broadband and strong EMW absorbers.

No abstract

Engineering microwave absorption materials with absorption in multiple bands and strong absorption performance in the C-band remains challenging to date.