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Metamaterials refer to a class of artificial composite structures with supernormal physical properties that natural materials do not have. The emergence of metamaterials has opened up new research directions for classical electromagnetic theory and made it possible to manipulate electromagnetic waves effectively. One of most important applications of metamaterials is metamaterial absorbers (MMAs). The properties of MMAs depend on the material composition, cell size and structure, which could often achieve "perfect" absorption through reasonable design. This review starts with the development of MMAs and describes the status of this absorber, then mainly focuses on bionic design and new artificial design. Specifically, it is to draw inspiration from natural plants and animals, design novel structures to get better absorbing properties. Furthermore, the artificial design can achieve the optimize absorption capacity as well as absorption bandwidth. What's more, this review summarizes the 3D printing technology to prepare MMAs that are different from traditional printed circuit board technology. The MMAs produced by 3D printing technology can prepare more complex shapes, and has light weight and better absorbing properties.

Perovskite LaCoO3 is of great potential in electromagnetic wave absorption considering its outstanding dielectric loss as well as the existing magnetic response with the magnetic doping. However, the dissipation mechanism of the magnetic doping on the microwave absorption is lack of sufficient investigated. In this paper, LaCo1-xFexO3 (x=0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, LCFOs) perovskites with different Fe doping amounts were prepared successfully by the sol-gel method and subsequent heat treatment in the air atmosphere. The structure characterization carried out by the first-principles calculations shows the effect of Fe doping on the dielectric and magnetic properties of LCFOs and the strong hybridization of Co/Fe-3d with O-2p in the LCFOs system was successfully demonstrated. Particularly, when x=0.1 and the thickness is only 1.95 mm, the LaCo0.9Fe0.1O3 exhibits the best microwave absorption performance with the minimum reflection loss (RL) value of about -41 dB. The typical samples achieve a broad effective absorption bandwidth (EAB) of 5.16 GHz (7.92-13.08 GHz), which covers the total X band (8-12 GHz). Considering that, the especial Fe doping perovskite is promising to be a candidate as efficient microwave absorbers.

Flexible and transparent conductive films are highly desirable in some optoelectronic devices, such as smart windows, touch panels, as well as displays and electromagnetic protection field. Silver nanowire (Ag NW) has been considered as the best material to replace indium tin oxide (ITO) to fabricate flexible transparent electromagnetic interference (EMI) shielding films due to its superior comprehensive performance. However, the common substrates supporting Ag NWs require surface modification to enhance the adhesion with Ag NWs. In this work, a flexible and transparent Ag NWs EMI shielding film with sandwich structure through a facile rod-coating method, wherein Ag NWs network were embedded between biodegradable gelatin-based substrate and cover layer. The interfacial adhesion between Ag NWs and gelatin-based layers was enhanced by hydrogen-bonding interaction and swelling effect without any pretreatment. The shielding effectiveness (SE) of the G/Ag NW/G (G represents gelatin-based layer) film reaches 37.74 dB at X band with an optical transmittance of 72.0 %. What’s more, the flexible gelatin-based layer and encapsulated structure endow the resultant G/Ag NW/G film integrating excellent mechanical properties, reliable durability, antioxidation, as well as anti-freezing performance. This work paves a new way for fabricating flexible transparent EMI shielding films.

To reduce electromagnetic (EM) wave interference pollution, in this work, carbon fibers@Co-ZIFs derivations (CFZD) as an advanced EM wave absorbing material was successfully prepared. The yolk-shell structure of the magnetic metal particles generated a large amount of contact area, facilitating the interface polarization and relaxation. As a result, the optimized sample delivers a maximum reflection loss (RL) value of -19.2 dB with a bandwidth of 2.6 GHz at a small thickness of 1.3 mm. Additionally, ANSYS Electronics Desktop 2018 (HFSS) was used to simulate the radar cross section (RCS) reduction in practical application based on these composites. The RCS values of composite coatings are less than -10 dBm2 at the range of -90°

The increasing growth of powerful and sophisticated electronic devices have an urgent need for excellent heat dissipation and electromagnetic interference shielding materials. However, few studies are focusing on one material with these properties. In this work, a novel hierarchically porous wood-derived carbon scaffold embedded phase change material was prepared via facile pyrolysis and vacuum infiltration process. Notably, the raw wood was pretreated by a delignification strategy, which makes great contributions to forming a hierarchically porous network and expanding the internal area after pyrolyzing. The results demonstrate that the honeycomb-like structure of the wood carbon scaffold was well maintained after calcination, which can provide a great number of channels for energy transmission and multi-reflection of electromagnetic waves. Moreover, the paraffin wax component as phase change material not only stores and releases numerous energies during the melting and solidification processes, but also endows the composite outstanding self-cleaning function. The present composite shows excellent energy storage property (the latent heat of 122.25 J/g) and satisfied electromagnetic interference shielding performance (average shielding effectiveness of 24.4 dB). Therefore, the synthesized porous wood carbon scaffold/paraffin wax composite has great potential in multifunctional, environmentally friendly thermal energy management and electromagnetic interference shielding applications.

Highlights The eco-friendly shaddock peel-derived carbon aerogels were prepared by a freeze-drying method. Multiple functions such as thermal insulation, compression resistance and microwave absorption can be integrated into one material-carbon aerogel. Novel computer simulation technology strategy was selected to simulate significant radar cross-sectional reduction values under real far field condition. . Abstract Eco-friendly electromagnetic wave absorbing materials with excellent thermal infrared stealth property, heat-insulating ability and compression resistance are highly attractive in practical applications. Meeting the aforesaid requirements simultaneously is a formidable challenge. Herein, ultra-light carbon aerogels were fabricated via fresh shaddock peel by facile freeze-drying method and calcination process, forming porous network architecture. With the heating platform temperature of 70 °C, the upper surface temperatures of the as-prepared carbon aerogel present a slow upward trend. The color of the sample surface in thermal infrared images is similar to that of the surroundings. With the maximum compressive stress of 2.435 kPa, the carbon aerogels can provide favorable endurance. The shaddock peel-based carbon aerogels possess the minimum reflection loss value (RLmin) of − 29.50 dB in X band. Meanwhile, the effective absorption bandwidth covers 5.80 GHz at a relatively thin thickness of only 1.7 mm. With the detection theta of 0°, the maximum radar cross-sectional (RCS) reduction values of 16.28 dB m2 can be achieved. Theoretical simulations of RCS have aroused extensive interest owing to their ingenious design and time-saving feature. This work paves the way for preparing multi-functional microwave absorbers derived from biomass raw materials under the guidance of RCS simulations.

Because of their unique three-dimensional cellular structure and intrinsic properties, polyimide foam materials have bright prospects for development in multiple functional equipment, which arouses extensive concern. In this Spotlight on Applications, several typical fabrication methods of polyimide foams and the related synthesis mechanism have been systematically described. The advantages and disadvantages of the preparation methods have been compared with each other. Representative functions and the corresponding mechanism models have been concluded, which involve thermal, mechanical, sensing, electromagnetic, environmental, and electrical fields. In the end, the severe tasks and challenges of polyimide foam materials have been summarized, and their promising future development is worth expecting.

The proliferation of electronic equipment and wireless communication technology has resulted in great convenience while simultaneously giving rise to the issue of electromagnetic interference (EMI). The deleterious effects of EMI on both unshielded electronics and human health have driven researchers to explore highly efficient electromagnetic (EM) wave absorbing and shielding materials to suppress EM radiation. Most reported powder EM wave absorbing and shielding (EMAS) materials are required to be further mixed with matrices to produce the composite coating layers. The complicated processing procedures restrict the application of these materials. Furthermore, such layers often suffer from poor durability. However, if EMAS materials are functionally and structurally integrated into a macrostructure, these drawbacks may be overcome. More importantly, EMAS materials with macrostructures can be integrated with other functions to satisfy ever-growing application demands in harsh environments. This review article discusses the design principles of advanced EMAS materials in terms of their macrostructures and multifunctions. Representative integrated macrostructures of EMAS materials and devices are introduced in detail. The multifunctionalities of some advanced EMAS materials, such as wearable, hydrophobic, and thermal insulating characteristics, are discussed as well. In the end, the current challenges and future directions for developing multifunctional EMAS materials are discussed.

With the continuous deterioration of the electromagnetic environment, there is an urgent need for exploring highly efficient and widely applicable electromagnetic interference shielding and microwave absorption materials. In current years, wood-based composites have been vastly investigated with low cost, light weight, sustainability, and an inherent porous and hierarchical structure. However, imperfect interfacial compatibility and electrical conductivity of wood are the main factors, which result in inferior electromagnetic interference shielding and microwave absorption performances. Meanwhile, the intrinsic defects of wood such as rotting and flammability also limit their practical applications. To overcome these shortcomings, improving the combination of each phase unit in micro–nano size and exploiting multi-functional composites are feasible solutions to optimize the electromagnetic properties of wood-based materials. In this review, the basic principles and mechanisms of electromagnetic interference shielding and microwave absorption are introduced comprehensively. Meanwhile, various wood-based electromagnetic interference shielding, microwave absorption composites, and their fabrication methods are discussed in detail. Furthermore, the perspectives and challenges in this field are put forth as well.

Silver nanowire (Ag NW) has been considered as the promising building block for the fabrication of transparent electromagnetic interference (EMI) shielding films. However, the practical application of Ag NW-based EMI shielding films has been restricted due to the unsatisfactory stability of Ag NW. Herein, we proposed a reduced graphene oxide (rGO) decorated Ag NW film, which realizes a seamless integration of optical transparency, highly efficient EMI shielding, reliable durability and stability. The Ag NW constructs a highly transparent and conductive network, and the rGO provides additional conductive path, showing a superior EMI shielding effectiveness (SE) of 33.62 dB at transmittance of 81.9%. In addition, the top rGO layer enables the hybrid film with reliable durability and chemical stability, which can maintain 96% and 90% EMI SE after 1000 times bending cycles at radius of 2 mm and exposure in air for 80 days. Furthermore, the rGO/Ag NW films also possess fast thermal response and heating stability, making them highly applicable in wearable devices. The synergy of Ag NW and rGO grants the hybrid EMI shielding film multiple desired functions and meanwhile overcomes the shortcomings of Ag NW. This work provides a reference for preparing multifunctional integrated transparent EMI shielding film.

High-performance electromagnetic (EM) wave absorption and shielding materials integrating with flexibility, air permeability, and anti-fatigue characteristics are of great potential in portable and wearable electronics. These materials usually prepared by depositing metal or alloy coatings on fabrics. However, the shortcomings of heavy weight and easy corrosion hamper its application. In this work, the cellulose nanofiber (CF) fabric was prepared by electrospinning technology. Then, conductive polyaniline (PANI) was deposited on the CF surface via a facile in-situ polymerization process. The interweaving cellulose/polyaniline nanofiber (CPF) composite constructs a conductive network, and the electrical conductivity can be adjusted by polymerization time. Benefiting from optimal impedance matching, strong conductive loss, as well as interfacial polarization, the CPF possesses excellent EM absorption performance. The minimum reflection loss (RLmin) value is −49.24 dB, and the effective absorption bandwidth (RL

Effectively broadening microwave absorbing frequency of pure magnetic substances remains a huge challenge. Herein, micro-perspective structures can be controlled through a calcination route. Satisfactorily, the composites prepared at the calcination temperature of 900 °C exhibit excellent microwave attenuation performance with a broad working frequency and appropriate paraffin filling ratio. Remarkably, the composites can reach an extremely high reflection loss (RL) value of − 49.79 dB, and the extended effective working frequency range (RL

Electromagnetic (EM) absorbers play an increasingly essential role in electronic information age, even towards coming intelligent life. The remarkable merits of heterointerface engineering and its peculiar EM characteristics inject a fresh and infinite vitality to design high-efficiency and stimuli-responsive EM absorbers. However, there still exist huge challenges in understanding and reinforcing these interface effects from the micro and macro perspectives. Herein, the EM response mechanisms of interfacial effects are dissected in depth, and advanced characterization as well as theoretical techniques is highly focused on. Then, the representative optimization strategies are systematically discussed with an emphasis on component selection and structural design. More importantly, the most cutting-edge smart EM functional devices based on heterointerface engineering are reported as highlights. Finally, current challenges and concrete suggestion are proposed, and future perspectives on this promising field are predicted as well. This article is protected by copyright. All rights reserved.

Confronting with increasing electromagnetic pollution, traditional microwave absorbing materials have their limitations, such as low yield and long preparation periods. At the same time, it is well established that electromagnetic simulation is an effective technology to enhance work efficiency, which can quickly explore the impedance matching conditions and electromagnetic characteristics to improve absorbing performance. Honeycomb structure has been widely used in the field of microwave absorption due to its light weight, high strength and heat resistance. This structure also possesses the advantages of multiple scattering, which is beneficial to microwave attenuation. In this work, Co/carbon (Co/C) particles with effective absorption bandwidth (EAB) (the band corresponding to the reflection loss value less than −10 dB) of 5.8 GHz were synthesized by a simple hydrothermal method. Whereupon through the high-frequency structure simulator (HFSS) electromagnetic simulation, Co/C absorbers with honeycomb structure were macroscopically designed, achieving an ultra-broad effective absorption bandwidth of 11.6 GHz. Herein, the effective combination of electromagnetic simulation and honeycomb structure design greatly improves the absorption bandwidth of Co/C. This work paves the way for designing microwave absorption materials with broad effective absorption bandwidth.