Electromagnetic Absorption Research Articles

Laser-forged transformation and encapsulation of nanoalloys: pioneering robust wideband electromagnetic wave absorption and shielding from GHz to THz

The emergence of the internet of things has promoted wireless communication’s evolution towards multi-band and multi-area utilization. Notably, forthcoming sixth-generation (6G) communication standards, incorporating terahertz (THz) frequencies alongside existing gigahertz (GHz) modes, drive the need for a versatile multi-band electromagnetic wave (EMW) absorbing and shielding material. This study introduces a pivotal advance via a new strategy, called ultrafast laser-induced thermal-chemical transformation and encapsulation of nanoalloys (LITENs). Employing multivariate metal-organic frameworks, this approach tailors a porous, multifunctional graphene-encased magnetic nanoalloy (GEMN). By fine-tuning pulse laser parameters and material components, the resulting GEMN excels in low-frequency absorption and THz shielding. GEMN achieves a breakthrough of minimum reflection loss of −50.6 dB in the optimal C-band (around 4.98 GHz). Computational evidence reinforces GEMN’s efficacy in reducing radar cross sections. Additionally, GEMN demonstrates superior electromagnetic interference shielding, reaching 98.92 dB under THz band (0.1–2 THz), with the mean value result of 55.47 dB. These accomplishments underscore GEMN’s potential for 6G signal shielding. In summary, LITEN yields the remarkable EMW controlling performance, holding promise in both GHz and THz frequency domains. This contribution heralds a paradigm shift in EM absorption and shielding materials, establishing a universally applicable framework with profound implications for future pursuits.

Agarics-derived porous Fe/C material activated by ZnCl2 and its enhanced microwave absorption performance

Biomass-derived carbon materials retain the unique porous structure of biological raw materials and have environmental advantages, making them a popular choice for electromagnetic microwave absorption research. The microwave absorption performance of biomass-derived carbon materials is largely influenced by their pore structure, which can be controlled by chemical activators. In this study, ZnCl2 was chosen as the activator and de-impregnated agarics with Fe(NO3)3·9 H2O for pretreatment. The Fe(NO3)3·9 H2O can provide magnetic Fe particles for the material to enhance the magnetic loss ability. And the weakly acidic ZnCl2 can avoid the pollution of the environment, and its dehydration and dehydroxylation properties can release the hydrogen and oxygen in the biomass char material in the form of water vapor, and release the hydrogen and oxygen in the biomass carbon material in the form of water vapor, and form a porous structure. porous structure. In addition, ZnCl2 will be converted to ZnO during the activation process, and the removal of ZnO by acid washing will increase the internal pore volume, form a conductive network, and form a rich three-dimensional interconnected pore structure. The pretreated samples were vacuum carbonized at high temperature to obtain agarics-derived porous Fe/C material, which is an excellent lightweight and high-performance microwave absorbing material. The resulting material has a wider absorption bandwidth and improved microwave absorption performance. At a thickness of 2.55 mm and a frequency of 8.31 GHz, the RLmin of Fe/C material is −51.14 dB. Furthermore, at a thickness of 2.13 mm, it has an effective absorption bandwidth of 3.63 GHz, covering most of the X-band.

Manipulating polarization attenuation in NbS2–NiS2 nanoflowers through homogeneous heterophase interface engineering toward microwave absorption with shifted frequency bands

Homogeneous heterogeneous (heterophase) interfaces regulated with low energy barriers have a fast response to applied electric fields and could provide a unique interfacial polarization, which facilitate the transport of electrons across the substrate. Such regulation on the interfaces is effective in modulating electromagnetic wave absorbing materials. Herein, we construct NbS2–NiS2 heterostructures with NiS2 nanoparticles uniformly grown in NbS2 hollow nanospheres, and such particular structure enhances the interfacial polarization. The strong electron transfer at the interface promotes electron transport throughout the material, which results in less scattering, promotes conduct ion loss and dielectric polarization relaxation, improves dielectric loss, and results in a good impedance matching of the material. Consequently, the absorbing band may be successful tuned. By regulating the amount of NiS2, the heterogeneous interface is finely alternated so that the overall wave-absorbing performance is shifted to lower frequencies. With a NiS2 content of 15 ​wt% and an absorber thickness of 1.84 ​mm, the minimum reflection loss at 14.56 ​GHz is −53.1 ​dB, and the effective absorption bandwidth is 5.04 ​GHz; more importantly, the minimum reflection loss in different bands is −20 dB, and the microwave energy absorption rate reaches 99% when the thickness is about 1.5–4.5 ​mm. This work demonstrates the construction of homogeneous heterostructures is effective in improving the electromagnetic absorption properties, providing guideline for the synthesis of highly efficient electromagnetic absorbing materials.

Enhancing mechanical properties of cementitious composites by boron nitride nanosheets modified carbon fiber

Carbon fiber (CF) is commonly employed to enhance the mechanical properties, electrical conductivity, and electromagnetic absorption properties of cementitious composites. However, its weak interfacial bonding with the matrix limits its application in such composites. In this study, boron nitride (BN) nanosheets were synthesized via the solid-state reaction and used to modify CF surface. The flexural and compressive strengths of cementitious composites incorporating BN nanosheets coated CF (BN@CF) increased by 18.45 % and 29.38 %, respectively, with CF doping at only 0.2 wt%. Isothermal calorimetry and TGA results revealed that BN nanosheets on CF surface would provide nucleation sites for the formation of C–S–H and CH. The microstructure and bonding properties of BN@CF were characterized using SEM/EDS, FTIR, XPS, finite element analysis, and single fiber pullout test. The results showed that the significant improvement of interfacial properties between the fiber and the matrix contributed to the increase of mechanical properties of cementitious composites. These findings provide an effective strategy for the strength development of CF-reinforced cementitious composites.

V-Based MXene/MAX Heterostructure Composites with Enhancing Dielectric Loss for Broadband Microwave Absorption.

Electromagnetic wave absorption performance is strictly dependent on attenuation and impedance matching, which are directly influenced by the ratio of MXene/MAX in the multilayer structured MXene/MAX composites. However, there is still a challenge to achieve collaborative optimization of dielectric loss and impedance matching by precisely regulating the proportional relationship of MXene/MAX. Herein, V-based MXene/MAX heterostructure composites with different V2C/V2AlC ratios were successfully synthesized by rationally controlling the temperature and time of the hydrothermal reaction. Experimental results indicated that V2C-100 °C-1 harvested the balance between reduced impedance matching and enhanced dielectric losses, which was attributed to the mildly enhanced conduction loss and polarization loss. The first principles indicated that abundant electrons migrate from the V atoms of the MXene to the C atoms of the MAX phase. The charge redistributed and accumulated at the interface, exciting the increase in the dielectric loss of V2C-100 °C-1. As a result, the V2C-100 °C-1 heterostructure composite had an excellent electromagnetic absorption effect with a minimum reflection loss of -50.06 dB and a wide effective absorption bandwidth of 4.0 GHz (12.72-16.72 GHz). This work provides a valuable experience for the development of efficient MXene-based microwave absorbing materials.

A popcorn-inspired strategy for compounding graphene@NiFe2O4 flexible films for strong electromagnetic interference shielding and absorption

Compounding functional nanoparticles with highly conductive and porous carbon scaffolds is a basic pathway for engineering many important functional devices. However, enabling uniform spatial distribution of functional particles within a massively conjugated, monolithic and mesoporous structure remains challenging, as the high processing temperature for graphitization can arouse nanoparticle ripening, agglomerations and compositional changes. Herein, we report a unique “popcorn-making-mimic” strategy for preparing a highly conjugated and uniformly compounded graphene@NiFe2O4 composite film through a laser-assisted instantaneous compounding method in ambient condition. It can successfully inhibit the unwanted structural disintegration and mass loss during the laser treatment by avoiding oxidation, bursting, and inhomogeneous heat accumulations, thus achieving a highly integrated composite structure with superior electrical conductivity and high saturated magnetization. Such a single-sided film exhibits an absolute shielding effectiveness of up to 20906 dB cm2 g−1 with 75% absorption rate, superior mechanical flexibility and excellent temperature/humidity aging reliability. These performance indexes signify a substantial advance in EMI absorption capability, fabrication universality, small form-factor and device reliability toward commercial applications. Our method provides a paradigm for fabricating sophisticated composite materials for versatile applications.

Efficient Design of Broadband and Low-Profile Multilayer Absorbing Materials on Cobalt-Iron Magnetic Alloy Doped with Rare Earth Element.

Magnetic metal absorbing materials have exhibited excellent absorptance performance. However, their applications are still limited in terms of light weight, low thickness and wide absorption bandwidth. To address this challenge, we design a broadband and low-profile multilayer absorber using cobalt-iron (CoFe) alloys doped with rare earth elements (REEs) lanthanum (La) and Neodymium (Nd). An improved estimation of distribution algorithm (IEDA) is employed in conjunction with a mathematical model of multilayer absorbing materials (MAMs) to optimize both the relative bandwidth with reflection loss (RL) below -10 dB and the thickness. Firstly, the absorption performance of CoFe alloys doped with La/Nd with different contents is analysed. Subsequently, IEDA is introduced based on a mathematical model to achieve an optimal MAM design that obtains a balance between absorption bandwidth and thickness. To validate the feasibility of our proposed method, a triple-layer MAM is designed and optimized to exhibit wide absorption bandwidth covering C, X, and Ku bands (6.16-12.82 GHz) and a total thickness of 2.39 mm. Then, the electromagnetic (EM) absorption mechanisms of the triple-layer MAMs are systematically investigated. Finally, the triple-layer sample is further fabricated and measured. The experimental result is in good agreement with the simulated result. This paper presents a rapid and efficient optimization method for designing MAMs, offering promising prospects in microwave applications, such as radar-stealth technology, EM shielding, and reduced EM pollution for electronic devices.

Development of carbon composite coatings for fire retardancy and electromagnetic interference shielding

This study has effectively showcased the feasibility of employing a carbon composite coatings, comprised of various carbon nanomaterials including carbon nanodots, carbon nanotubes, and graphene nanosheets integrated within a matrix of sodium metasilicate + gypsum, for applications in both flame retardancy and electromagnetic interference (EMI) shielding. The resulting carbon composite coatings, when applied to wooden substrates, demonstrate remarkable fireproof performance, as validated through fire injections at temperatures as high as 1050 °C. This underscores the pivotal role plays by the design of carbon composites in suppressing flame propagation and charring, leading to reduced carbonization areas. Thermogravimetric analysis further reveals that the carbon composite coating generates substantial char residue at 800 °C, signifying enhanced thermal insulating properties derived from the robust composite carbon architecture. Furthermore, the carbon composite coatings show a significant decrease in electromagnetic fields (electric field around 50 % and magnetic field around 44 %), indicating their efficient EMI shielding properties. This improved EMI shielding performance may be due to the deliberate insertion of CNs into the composite materials, which fine-tunes resistance and dielectric loss while allowing effective electromagnetic absorption by the carbon composites. The breakthroughs made in flame retardancy and EMI shielding highlight carbon composites as superior strengthens to flame-retardant and EMI-absorbing building coatings.

Synchronous enhancement and broadening of dielectric loss and magnetic loss induced by substituted Gd in GdFeO3-encapsulated Fe (Gd) nanoparticles

Synchronous enhancement and broadening of dielectric loss and magnetic loss is a key factor for achieving excellent microwave absorption behavior. However, one term’s reinforcement always comes at the expense of the other one. In this work, a new kind of core-shell structured nanoparticle has been designed and prepared by arc-discharge method, in which GdFeO3 is shell and Fe (Gd) solid solution works as core, respectively. Except for the typical interfacial polarization and natural resonance, the new dipole induced by asymmetric electric charge arising from substituted Gd in Fe lattice results in enhanced and broadened dielectric loss, and the strong local magnetic anisotropy induced by intensive magnetic Fe-Gd coupling between 3d-4 f electrons leads to enhanced and broadened magnetic loss. Synchronously widened and enhanced dielectric and magnetic loss ensure that GdFeO3-encapsulated Fe(Gd) nanoparticles have effective absorption bandwidth of 4.16 GHz (10.48–14.64 GHz) at 2.3 mm, compared with that (2.32 GHz at 4.9 mm) of Fe nanoparticles. This study develops an approach for synchronously enhancing dielectric loss and magnetic loss, which has potential for achieving excellent EM absorption behaviors.

Tailoring surface terminals on MXene enables high-efficiency electromagnetic absorption

MXene (Ti3C2Tx) is an important category of two-dimensional (2D) materials due to its distinctive metallic conductivity and adjustable surface chemistry. The exceptional benefits of heterointerface and defects or viods, combined with the distinct electromagnetic (EM) properties, inject boundless potential into the advancement of MXene-based absorbers for EM absorbing materials. However, conventional synthetic methods depend on chemical etching of MAX powders (Ti3AlC2) using hazardous HF or similar substances, resulting in MXene sheets with fluorine termination and limited stability in colloidal dispersions under ambient conditions. Herein, varied synthetic routes were proposed to prepare MXenes with different terminal groups by the fluoride-based salts, fluoride-free molten salts, and alkali etching. 2D MXene nanosheets with abundant surface groups are excellent EM absorbing materials, and the MXene etched by the Lewis acid CuCl2 delivered remarkable reflection loss (RL) value of −47.56 dB at 2.5 mm and broad bandwidth of 4.8 GHz due to promoted interfacial polarization. By conducting a thorough examination of the structural changes in MXenes, this study aims to propose a viable method for delaminating single-layer MXene and elucidate the EM absorption mechanisms.

Construction of Fe7S8 anchoring S-doped porous graphene with enhanced multi-band electromagnetic absorptions

At present, research bottleneck on electromagnetic absorption materials lied in achieving strong absorption with broadband and multi-band responses. In this paper, Fe7S8 anchoring S-doped porous graphene was synthesized for multi-band electromagnetic absorptions. Rhodanine played the role of ‘two birds in one stone’, converting Fe3O4 to Fe7S8 and constructing porous S-doped carbon. The hybrids exhibited multi-band electromagnetic absorptions at 10.52, 12.56 and 15.03 GHz, with effective bandwidth achieved up to 12.07 GHz. This paper showcases reference path for the design of multi-band electromagnetic absorption materials.

Microfluidic Metasurfaces: A New Frontier in Electromagnetic Wave Engineering

AbstractMetasurfaces, as 2D artificial electromagnetic materials, play a pivotal role in manipulating electromagnetic waves by controlling their amplitude, phase, and polarization. Achieving this control involves designing subwavelength meta‐molecules with specific geometries and periodicities. In the context of microfluidic metasurfaces, optical properties can be dynamically modulated by altering either the geometric structure of liquid meta‐molecules or the refractive index of the liquid medium. Leveraging the fluidity of liquid materials, microfluidic metasurfaces exhibit remarkable performance in terms of reconfigurability and flexibility. These properties not only establish a cutting‐edge research area but also broaden the scope of applications for active metasurface devices. Additionally, the integration of metasurfaces within microfluidic systems has led to novel functionalities, including enhanced particle manipulation and sensor technologies. Compared to conventional solid‐material‐based metasurfaces, microfluidic metasurfaces offer greater design freedom, making them advantageous for diverse fields such as electromagnetic absorption, optical sensing, holographic displays, and tunable optical meta‐devices like flat lenses and polarizers. This review provides insights into the characteristics, modulation techniques, and potential applications of microfluidic metasurfaces, illuminating both the current research landscape and promising avenues for further explorations.

Multi-interface spatial star-like MoC/Co/C composites toward enhanced electromagnetic wave absorption properties

Interfacial engineering and morphology design are two popular strategies to strengthen the performance of carbon-based composites as electromagnetic wave absorbing materials (EWAMs). Herein, we integrate their advantages simultaneously in ternary MoC/Co/C composites (SMCCs). On one hand, highly dispersed MoC and Co nanoparticles create abundant heterogeneous interfaces, and on the other hand, the spatial star-like carbon skeletons derived from ZnCo-MOF also bring significant structure contribution to EM energy consumption. EM measurement reveals that the pyrolysis temperature greatly impacts EM properties of SMCCs. After blending with paraffin (organic binder), the mixture that involves SMCC-800 (pyrolyzed at 800 °C) may have both good impedance matching degree and powerful EM attenuation ability. As a result, SMCC-800/paraffin displays excellent EM absorption performance, including strong reflection loss intensity down to −67.3 dB at 16.2 GHz (thickness: 1.8 mm) and broad response bandwidth of 6.0 GHz (12.0–18.0 GHz, thickness: 2.0 mm) less than −10.0 dB, which outdo the performance of many composites with similar chemical composition ever reported. The EM absorption mechanism of SMCC-800/paraffin is comprehensively illustrated through the investigation on EM properties of the mixtures with various control samples.

Electromagnetic waves absorbing performance of cypress cone derived activated carbon decorated by magnetite nanoparticles

Biomass-based porous magnetic nanocomposites were prepared for microwave absorption in the X-band range. Fe3O4 nanoparticles were precipitated on activated carbon (AC) derived from cypress cones, creating composites with carbon contents ranging from 15 to 85 % by weight. Absorption experiments revealed that 15 % wt. nanocomposite exhibited optimal performance, showing a minimum reflection loss (RLmin) of −16.3 dB at a thickness of only 2.5 mm. Notably, this composites efficient absorption bandwidth covered 80 % of the X-band at this thin dimension. This study highlights the potential of this nanocomposite as an effective electromagnetic absorption material. Cole-Cole diagrams confirmed the multiple polarization and conduction losses. The impedance mismatch plot and attenuation constant represent significant impedance matching with free space and high dissipation, which improves the performance of nanocomposites with a ferrite/AC ratio of 85:15.

Mechanical properties and electromagnetic wave absorption characteristics of solid waste low-carbon cementitious materials

A low-carbon multi-functional cement substitute material has been developed to reduce electromagnetic pollution in building spaces and protect human health. The solid waste electromagnetic absorption cementitious material (SWEACM) is produced by combining steel slag (SS), blast furnace slag (BFS), and phosphogypsum (PG). In this study, the properties of SWEACM were analyzed, including flow, electromagnetic wave absorption, strength, and environmental properties. Additionally, the hydration and electromagnetic wave absorption mechanisms were examined. The results indicate that SS, BFS, and PG content significantly affect the strength and electromagnetic wave absorption properties of SWEACM. S-6 exhibits the best overall performance (SS: BFS: PG = 3:6:1), with the highest strength (28 days compressive strength = 33.5 MPa) and fluidity (19.1 cm). Furthermore, it has excellent electromagnetic absorption performance (RLmin = −45.4 dB), with an adequate absorption bandwidth of up to 10 GHz in the 2–18 GHz range. The excellent electromagnetic wave absorption capability of SWEACM is mainly due to the resonance, polarization relaxation loss, and conduction loss of the magnetic and conductive components in the material. The results show that SWEACM can be used as a multi-functional construction engineering material for electromagnetic protection, combining high levels of high electromagnetic wave absorption, strength performance, and environmental benefits.

Microwave-Assisted Hydrothermal Synthesis of Nanosheet Layered Hexagonal Spinel Ferrites for Efficient Electromagnetic Wave Absorbing.

A microwave-induced combustion method has been utilized to prepare nanosized powders of hexagonal spinel ferrites using urea and glycine as fuel. The structural and electromagnetic absorption of these products was investigated using X-ray diffraction (XRD). From the (3,1,1) and (1013) peaks in XRD measurements, it was seen that the samples we synthesized were nanosized spinel and y-phase hexagonal ferrite. In addition, Fourier-transform infrared measurements showed that the synthesized samples had high absorption values showing Fe-O, which is between 878 to 4000 cm-1, and metal-oxygen transitions, which are between the 700 and 2500-3000 cm-1 in the spinel and hexagonal phases. From the scanning electron microscope image of the particles, it is seen that they are homogeneous, filled structures with ∼35-40 nm. It appears from vector network analyzer measurements that the synthesized 1.5 mm thick composite materials have very high electromagnetic absorption properties and that these composites can also be used in electromagnetic interference, Wi-Fi applications, and health.

Dual-modified catalytic core-shell structure biomass carbon cotton fiber extends broadband electromagnetic waves absorption applications

Using vacuum impregnation method, the biomass carbon cotton fiber material was modified with polymer-derived SiCN ceramics and different Ni sources to successfully prepare the composite material. The electromagnetic microwave absorption properties of the material in the range of 2–18 GHz and the catalytic effect of different nickel sources were studied. The material modified by nickel nitrate hexahydrate forms a carbon fiber coated structure, improves impedance matching, enriches heterostructures, and increases electromagnetic synergistic loss, effectively enhancing the effective absorption bandwidth (EAB) reaches 4.72 GHz, the minimum reflection loss (RLmin) is −47.79 dB, and the thickness is only 1.32 mm. The results of CST show that the radar cross section of CFPN-2 material is −36.86 dB m2, and it has obvious effect of optimizing impedance matching.

Intelligent Tunable Wave-Absorbing CNTs/VO2/ANF Composite Aerogels Based on Temperature-Driving.

The development of new electromagnetic absorbing materials is the main strategy to address electromagnetic radiation. Once traditional electromagnetic wave-absorbing materials are prepared, it is difficult to dynamically change their electromagnetic wave-absorbing performance. Facing the complexity of the information age and the rapid development of modern radar, it is significant to develop intelligent modulation of electromagnetic wave-absorbing materials. Here, CNTs/VO2/ANF composite aerogels with dynamic frequency tunability and switchable absorption on/off were synthesized. Based on the phase change behavior of VO2, the degree of polarization and interfacial effects of multiple heterogeneous interfaces between VO2 and CNTs and aramid nanofibers (ANFs) were modulated at different temperatures. With the increase in temperature (from 25 to 200 °C), the maximum absorption frequency of the frequency tunable aerogel is modulated from 12.24 to 8.56 GHz in the X-band, and the absorption intensity remains stable. The maximum effective switching bandwidth (ΔEAB) of the wave-absorbing switchable aerogel is 3.70 GHz. This study provides insights into intelligent electromagnetic wave absorption performance and paves the way for temperature-driven application of intelligent modulation of electromagnetic absorbers.

A hollow carbonized kapok fiber/nano CoFe2O4 composite for broad bandwidth and enhanced microwave absorber

The development of intelligent and portable electrics necessitates the creation of an enhanced electromagnetic absorption and broad bandwidth microwave absorber. The synthesis of nano cobalt ferrite (CoFe2O4; CFO) combined with hollow carbonized kapok fiber by the Sol-Gel method and annealing process is a promising approach. The microwave absorption of carbonized kapok fiber/CFO was enhanced, and the bandwidth broadened due to the dielectric loss microwave absorber carbonized kapok fiber synergizing with the magnetic loss microwave absorber CFO. The results demonstrated that the minimal reflection loss of carbonized kapok fiber/CFO-6 was −52.2 dB at 8.56 GHz, with a thickness of 3.37 mm, and the broadest effective absorbing bandwidth was 6.2 GHz, with a thickness of 2.31 mm. The simulation results, which were obtained using the CST MWS software, exhibited a high degree of agreement with those obtained from the experimental measurements. The strategy offers a prospective method for the preparation of enhanced absorption and broad bandwidth microwave absorbers.

Customized heterostructure of transition metal carbides as high-efficiency and anti-corrosion electromagnetic absorbers

The ever-increasing presence of electronic devices and communication equipment imposes a critical demand for the development of highly efficient microwave absorption materials, as a means to combat the detrimental effects of electromagnetic (EM) wave pollution. The extraordinary advantages offered by heterointerface and defect engineering, coupled with their distinctive electromagnetic traits, infuse boundless energy into the development of MXene-based absorbers for EM attenuation. However, there is still a lack of understanding regarding the consequences of irreversible oxidation on the surface chemistry and dielectric properties of MXenes. Through the employment of heterointerface engineering strategy to promote interfacial charge accumulation and polarization, remarkable EM absorption properties coupled with corrosion resistance have been realized. The partially oxidized MXenes, particularly Ti3C2Tx and V2CTx, displayed remarkable reflection loss (RL) values of −56.83 dB and −52.13 dB, respectively. Additionally, the Nb2CTx composites showcased exceptional performance, offering a significantly broader bandwidth of 9.84 GHz. By conducting an extensive examination of the structural changes in MXenes, this work aims to elucidate the oxidation mechanisms and proposes a feasible method for producing MXenes with excellent absorption properties.