Effective Electromagnetic Wave Research Articles

Structural Design for EMI Shielding: From Underlying Mechanisms to Common Pitfalls.

Modern human civilization deeply relies on the rapid advancement of cutting-edge electronic systems that have revolutionized communication, education, aviation, and entertainment. However, the electromagnetic interference (EMI) generated by digital systems poses a significant threat to the society, potentially leading to a future crisis. While numerous efforts are made to develop nanotechnological shielding systems to mitigate the detrimental effects of EMI, there is limited focus on creating absorption-dominant shielding solutions. Achieving absorption-dominant EMI shields requires careful structural design engineering, starting from the smallest components and considering the most effective electromagnetic wave attenuating factors. This review offers a comprehensive overview of shielding structures, emphasizing the critical elements of absorption-dominant shielding design, shielding mechanisms, limitations of both traditional and nanotechnological EMI shields, and common misconceptions about the foundational principles of EMI shielding science. This systematic review serves as a scientific guide for designing shielding structures that prioritize absorption, highlighting an often-overlooked aspect of shielding science.

Synthesis of Hierarchical CF@Fe3O4 Fibers Decorated with MoS2 Layers Forming Core-Sheath Microstructure toward Tunable and Efficient Electromagnetic Wave Absorption.

Hierarchical structural design has been verified as a feasible strategy to fabricate effective electromagnetic wave (EMW) absorbers, so we designed hierarchical core-sheath composites with magnetic particles and dielectric layers. In this work, a hierarchical structure of carbon fiber (CF)@Fe3O4@MoS2 (CPDF7-M) was prepared by introducing Fe3O4 and depositing MoS2 layers on the surface of fibers. Due to the synergistic effects from the CF@Fe3O4 increasing the conductive and magnetic loss and the outer MoS2 layers improving the impedance matching, the optimal reflection loss (RL) value was -63.1 dB at 2.7 mm and the effective absorption bandwidth (EAB) was 9.1 GHz covering the X and Ku band. Moreover, the EAB values were adjusted with a specific MoS2 loading at different thicknesses, which provided the necessary reference for the construction of efficient and flexible absorbers in the EMW absorption fields.

N, O-Doped Walnut-Like Porous Carbon Composite Microspheres Loaded with Fe/Co Nanoparticles for Adjustable Electromagnetic Wave Absorption.

This study addresses the challenge of designing simple and environmentally friendly methods for the preparation of effective electromagnetic wave (EMW) absorbing materials with tailored microstructures and multi-component regulation. N, O doped walnut-like porous carbon composite microspheres loaded with FeCo nanoparticles (WPCM/Fe-Co) are synthesized through high-temperature carbonization combined with soap-free emulsion polymerization and hydrothermal methods, avoiding the use of toxic solvents and complex conditions. The incorporation of magnetic components enhances magnetic loss, complementing dielectric loss to optimize EMW attenuation. The unique walnut-like morphology further improves impedance matching. The proportions of Fe and Co components can be adjusted to regulate the material's reflection loss, thickness, and bandwidth, allowing for fine-tuning of absorption performance. At a low filling ratio (16.7%), the optimal WPCM/Fe-Co composites exhibit a minimum reflection loss (RLmin ) of -48.34dB (10.33GHz, 3.0mm) and an overall effective absorbing bandwidth (EAB) covering the entire C bands, X bands, and Ku bands. This work introduces a novel approach to composition regulation and presents a green synthesis method for magnetic carbon composite absorbers with high-performance EMW absorption at low loading.

Frequency tunable Ni–Ti‐substituted Ba–M hexaferrite for efficient electromagnetic wave absorption in 8.2–75 GHz range

The development of 5G telecommunication technology has seen a high demand for effective electromagnetic (EM) wave absorbers in the millimeter wave (mmWave) band. Because hexagonal M‐type ferrite is known to have high ferromagnetic resonance (FMR) in the 5G band frequency, it has attracted significant attention as a mmWave absorber. However, study of the relationship between magnetocrystalline anisotropy, FMR frequency, and EM wave absorption performance in the mmWave band remains insufficient. In this study, Ni–Ti‐substituted M‐type barium ferrite (Ba–M ferrite) was synthesized using the citrate sol–gel method, and the change in the magnetic properties caused by Ni–Ti substitution was analyzed. The complex permittivity, permeability, and reflection loss (RL) of the Ni–Ti‐substituted Ba–M ferrite composites in the 8.2–75 GHz broadband frequency range were also studied. The EM wave absorption frequency, which is governed by the FMR frequency, could be tuned by controlling the amount of substituted Ni–Ti ions in the Ba–M ferrite. The prepared EM wave absorber exhibited excellent EM wave absorption properties with an RL of −52 dB at 29.5 GHz and a matching thickness of 0.95 mm. This study provides insights into a frequency‐tunable EM wave absorber with enhanced absorption properties, attained by changing the magnetic properties of Ni–Ti‐substituted M‐type hexaferrites in the mmWave frequency band.

Metal organic framework-derived hierarchical 0D/1D CoPC/CNTs architecture interlaminated in 2D MXene layers for superior absorption of electromagnetic waves

Nowadays, exploring effective electromagnetic wave (EMW) absorbing materials with ultrathin thickness, lightweight, broad absorption bandwidth, and robust absorption capability is crucial to solve EMW pollution issues. Ti3C2Tx is a potential candidate for effective EMW absorbing materials by virtue of its low density, excellent electrical conductivity, high specific surface area, and tunable terminal groups. However, the intrinsic attenuation mechanisms of single dielectric absorbers are limited for practical requirements. Herein, 0D/1D/2D architecture of CoPC/CNTs@MXene hybrids with 0D cobalt nanoparticles supported on porous carbon, 1D carbon nanotubes and 2D Ti3C2Tx nanosheets have been conceptualized and fabricated successfully. By pyrolyzing bimetallic ZnCo-MOF at 800 °C, a 0D/1D hierarchical CoPC/CNTs sample was initially produced, subsequently interlaminated between the Ti3C2Tx matrix via electrostatic self-assembly to fabricate CoPC/CNTs@MXene (CCM) absorbers. The impedance matching properties was optimized by modifying the CoPC/CNTs content. Remarkably, CCM-20 hybrids achieved strong EMW absorption capability (reflection loss of −54.2 dB) at 5.56 GHz, and CCM-30 hybrids achieved ultrathin (1.8 mm) and a broad effective bandwidth (EAB) below − 10 dB (5.6 GHz), which is superior to the magnetic-dielectric hybrids with comparable components reported previously. The exceptional absorption capability can be attributed to the synergistic effects of interface polarizations and magnetic loss. The intricate construction of the 0D/1D/2D architecture facilitates the multiple reflections and scattering of EMW. This work provides an idea for fabricating MXene-based composites with remarkable electromagnetic properties and a broad absorption bandwidth for potential applications.

Microwave absorption performance of M-type hexagonal ferrite and MXene composite in Ka and V bands (5G mmWave frequency bands)

Lightweight and thin electromagnetic interference (EMI) shielding materials with high shielding effectiveness (SE) have been investigated over the last decade to address the unreliability issue in all electronic technologies caused by EMI. Herein, we report the SE of the novel Ti3C2Tx MXene/doped-hexaferrite (hexagonal ferrite: BaCo0.3Ti0.3Fe11.4O19) composite. This composite suppresses electromagnetic (EM) waves dominantly via absorption over the frequency range from 30 to 50 GHz for millimeter-wave (mmWave) applications. Two-dimensional inorganic compound Ti3C2Tx MXene was synthesized using the LiF-HCl etching process, and doped-hexaferrite particles were prepared using a conventional solid-state reaction. Then, the MXene/doped-hexaferrite composite was fabricated by mixing MXene/polyvinyl-pyrrolidone (PVP) containing solution with the hexaferrite particles. The composites were characterized by a vibrating sample magnetometer for static magnetic properties and a vector network analyzer for dynamic magnetic and dielectric properties and microwave absorbing performance.A high magnetocrystalline anisotropy of hexaferrite shifted the microwave absorption peak to mmWave bands such as Ka- and V-bands, unlike spinel ferrite. The 1.5 mm thick MXene/45 wt% doped-hexaferrite composite shows a broad effective bandwidth (reflection loss (RL) less than 10 dB) of 7 GHz in the frequency range from 38 to 45 GHz. This excellent absorbing performance is mainly attributed to improved impedance matching and enhanced dielectric and magnetic losses of the composite. It was found that the SE was dominated by absorption instead of reflection.The experimental results demonstrate that the MXene/BaCo0.3Ti0.3Fe11.4O19 hexaferrite composite can be a promising and effective EM wave absorber material for millimeter-wave applications such as the fifth-generation (5G) network and opens up new opportunities for THz (6G network) EMI materials development.

Dielectric Loss Mechanism in Electromagnetic Wave Absorbing Materials.

Electromagnetic (EM) wave absorbing materials play an increasingly important role in modern society for their multi‐functional in military stealth and incoming 5G smart era. Dielectric loss EM wave absorbers and underlying loss mechanism investigation are of great significance to unveil EM wave attenuation behaviors of materials and guide novel dielectric loss materials design. However, current researches focus more on materials synthesis rather than in‐depth mechanism study. Herein, comprehensive views toward dielectric loss mechanisms including interfacial polarization, dipolar polarization, conductive loss, and defect‐induced polarization are provided. Particularly, some misunderstandings and ambiguous concepts for each mechanism are highlighted. Besides, in‐depth dielectric loss study and novel dielectric loss mechanisms are emphasized. Moreover, new dielectric loss mechanism regulation strategies instead of regular components compositing are summarized to provide inspiring thoughts toward simple and effective EM wave attenuation behavior modulation.

Core-shell structured nanocomposites formed by silicon coated carbon nanotubes with anti-oxidation and electromagnetic wave absorption

The silicon coated Carbon nanotubes (CNTs) nanocomposite (CNTs@Si) with a shell structure was successfully synthesized by a simple chemical vapor deposition (CVD) method. In this work, the CNTs@Si is not only introduced as a structural material providing oxidation performance, but also as an extremely effective electromagnetic wave (EMW) absorption nanocomposite. Dielectric characteristics EMW absorption properties within the frequency range of 2–18 GHz of CNTs@Si were studied, and the oxidation resistance of CNTs@Si was characterized. Due to the dense space conductive network formed by CNTs, the EMW absorbing properties of CNTs@Si nanocomposite features excellent electromagnetic wave absorption capacity at a filling amount of 1%. The maximum reflection loss (RL) reaches −61.57 dB at the thickness of 1.8 mm, and a wide effective absorption bandwidth (EAB, RL < −10 dB) of 2.88 GHz is achieved. The obtained CNTs@Si core-shell nanocomposites exhibit excellent antioxidant performance and absorbing performance due to silicon bridging. Efficient electromagnetic wave absorption and excellent oxidation resistance of CNTs@Si can be regarded as a brand-new competitive candidate for EMW absorption materials in harsh environment.

Surface Modification of Activated Carbon Fibers with Fe3O4 for Enhancing Their Electromagnetic Wave Absorption Property

In this study, the porous activated carbon fiber (ACF) is prepared by viscose fiber, and Fe3O4 coating is deposited on the surface of ACF through in situ hybridization to prepare carbon/magnetic electromagnetic (EM) wave absorption materials. Compared with pure Fe3O4 and ACF, the EM wave absorption rate is improved. When the solubility of FeCl3 is 2 mol/L and the thickness of the prepared ACF–Fe3O4(3) EM wave absorption material is 3 mm, the EM wave loss at 10 GHz reaches −44.3 dB and effective EM wave absorption bandwidths ( reflection loss RL &lt; − 10 dB and RL &lt; − 20 dB) reached 4.8 GHz (8.8–13.6 GHz) and 1.1 GHz (9.3–10.4 GHz), respectively. The prepared ACF-based composite material has a light structure and strong absorption bandwidth. Findings can provide references for the research on other EM wave-absorbing materials.

Electromagnetic wave absorbing performance of multiphase (SiC/HfC/C)/SiO2 nanocomposites with an unique microstructure

Dielectric properties and electromagnetic (EM) wave absorbing performance of monolithic (SiC/HfC/C)/SiO2 nanocomposites (denoted as SHCOs) have been investigated in the X-band (8.2–12.4 GHz). The multiphase SHCOs are composed of insulating SiO2 and SiC/HfC/C nanocomposite fillers (SHC), which fillers composed of semiconducting β-SiC, conductive HfC-Carbon core-shell nanoparticles, and interconnected carbon nanoribbons. Dielectric response indicates that the increased SHC content results in an enhanced imaginary part of the permittivity and dielectric loss, leading to an improved EM absorbing performance. The unique microstructure with an EM wave-transparent SiO2 matrix is favorable for impedance matching and effective EM wave propagation. The enhanced interface polarization and conduction loss are considered as the key mechanisms for EM wave attenuation. The minimum reflection loss of the SHCOs achieves – 60.7 dB containing 20 vol% of SHC (at 9.98 GHz) with the sample thickness of 3.33 mm, and the effective absorbing bandwidth (EAB) covers ca. 72 % of the X-band. The monolithic (SiC/HfC/C)/SiO2 nanocomposites with outstanding EM wave absorbing performance are promising candidates for EM application at high temperatures.

Facile Synthesis of Ultralight and Porous Melamine-Formaldehyde (MF) Resin-Derived Magnetic Graphite-Like C3N4/Carbon Foam with Electromagnetic Wave Absorption Behavior

Society demands effective electromagnetic wave (EMW) absorbers that are lightweight, with a broad absorption band and strong absorption, to solve excessive electromagnetic radiation. Herein, ultralight magnetic graphite-like C3N4/carbon foam (MCMF) was fabricated via impregnating polymerized melamine formaldehyde (MF) foams in Fe3O4 nanoparticle solution, followed by in situ pyrolysis at 1000 °C. MCMF possesses porous architectures consisting of graphitic C3N4/carbon and CFe15.1. The magnetic particles (α-Fe, Fe3O4 and Fe3C) were formed and modified on the internal skeleton surface. The EMW absorption capacity of MCMF is better than the that of carbonized MF foam without Fe3O4 (CMF), possessing excellent absorption behavior, with a minimum RL value of −47.38 dB and a matching thickness as thin as 3.90 mm. The corresponding effective absorbing bandwidth is as broad as 13.32 GHz. Maxwell–Wagner–Sillars (MWS) polarization and the residual loss are proved to be beneficial for such superior absorption behavior. Besides, graphitic C3N4 enriches the interface polarization effect and the electromagnetic matching effect. The microporous structures are beneficial for increasing EMW propagation, resulting in internal multiple reflections and scatterings, which are also beneficial for EMW attenuation.

Lattice composites with embedded short carbon fiber/Fe3O4/epoxy hollow spheres for structural performance and microwave absorption

Lightweight absorption materials with superior mechanical properties have received significant attention owing to their potential for use in military stealth and electromagnetic protection applications. Herein, a novel electromagnetic (EM) wave absorbing lattice structured composite material containing a hollow short carbon fiber (SCF)/Fe3O4/epoxy sphere filler, and an epoxy resin matrix, is described. The morphology, density, and isostatic compression strength of the hollow SCF/Fe3O4/epoxy spheres were measured, and the mechanical and electromagnetic wave absorption properties of the epoxy resin composite embedded with the hollow SCF/Fe3O4/epoxy spheres were studied. The results indicate that the composite possessed a high compression strength of ~57.3 MPa with a density of only ~0.92 g/cm3. Furthermore, the effective absorption bandwidth within the range of 2–18 GHz of the composite was 1.8 GHz, with an ultra-thin equivalent thickness of only ~0.48 mm. The macro-sized hollow structure spheres were effective EM wave absorption enhancements, and the lattice composite embedded with these hollow spheres presented a unique structure and excellent absorption performance.

Molybdenum Disulfide Quantum Dots Prepared by Bipolar-Electrode Electrochemical Scissoring.

A convenient bipolar-electrode (BPE) electrochemical method was engineered to produce molybdenum disulfide (MoS2) quantum dots (QDs) using pure phosphate buffer (PBS) as the electrolyte and the MoS2 powder as the precursor. Meanwhile, the corresponding by-product precipitate was studied, in which MoS2 nanosheets were observed. The BPE design would not be restricted by the shape and size of the MoS2 precursor. It could lead to the defect generation and 2H → 1T phase variation of the MoS2, resulting in the formation of nanosheets and finally the QDs. The as-prepared MoS2 QDs exhibited high photoluminescence (PL) quantum yield of 13.9% and average lateral size of 4.4 ± 0.2 nm, respectively. Their excellent PL property, low cytotoxicity, and good aqueous dispersion offer promising applicability in PL staining and cell imaging. Meanwhile, the as-obtained byproduct containing the nanosheets could be used as an effective electromagnetic wave (EMW) absorber. The minimum reflection loss (RL) value was −54.13 dB at the thickness of 3.3 mm. The corresponding bandwidth with efficient attenuation (<−10 dB) was up to 7.04 GHz (8.8–15.84 GHz). The as-obtained EMW performance was far superior over most previously reported MoS2-based nanomaterials.

Porous C/Ni composites derived from fluid coke for ultra-wide bandwidth electromagnetic wave absorption performance

Both morphological structure and chemical composition are indispensable factors for the design and fabrication of high-performance electromagnetic (EM) wave absorbers. Herein, we prepare a porous carbon composite material with high surface area by using recycled fluid coke as starting material via an alkaline activation process. The minimum reflection loss of the activated fluid coke (AFC-3.5) is −20 dB, while the effective absorption frequency band is 4.8–18 GHz. Ni nanocrystals subsequently grow in-situ and embed uniformly within porous framework of activated fluid coke to form porous carbon/Ni (C/Ni) composites. As a result, the lowest reflection loss value is further reduced to −47 dB, while effective EM wave absorption band (RL < −10 dB) covers wider frequency ranges from 3.5 to 18 GHz with a low filler loading of 20 wt%. We also present the absorption mechanism of the porous structure and chemical composition. This work demonstrates the significance in exploring porous structures for the application of EM wave absorption, and for further research and development of novel EM wave absorption materials.

Electromagnetic Wave Absorber with Multiple Resonance Periodic Pattern Design for Oblique Incidence

The application of EM (electromagnetic) wave absorbers for commercial and military purposes is undergoing expansion. For military applications, EM wave absorbers minimize the RCS (radar cross section) of aircraft structures, thereby reducing the possibility of detection by radar. In this study, a composite structure, which is capable of absorbing EM waves, and which contains a square periodic patterned layer is presented. It is shown that the control of pattern geometry and surface resistance induces multi-resonance for wide-band absorption on the composite structures. The characteristics are useful for multiple-reflection structures, which show effective EM wave absorption against oblique incidence waves. A novel concept of a wide-band RAS (radar absorbing structure) is proposed and the EM wave-absorbing characteristics are designed for incidence angle variation. As a result, the approach followed on the RAS for multiple-reflection structures is verified with a dihedral structure.

Cobalt doping-induced strong electromagnetic wave absorption in SiC nanowires

Understanding the electronic structure-property relationship in doped systems is a prerequisite to designing functional materials. We fabricated Co-doped SiC nanowires with different Co contents by a facile carbothermal reduction approach. The nanowires were characterized in terms of microstructure, electronic structure, and electromagnetic (EM) parameters to uncover the effect of Co dopants on enhancing the EM wave absorption ability. Microstructure analysis and density functional theory calculations verified that the doped Co species inhibited the formation of stacking faults and point defects and increased the conductivity of Co-doped SiC nanowires, which indicated the dominant role of conductivity in enhancing dielectric loss. The Co dopants also imparted the Co-doped SiC nanowires with distinct room-temperature ferromagnetic property, which led to enhanced magnetic loss and impedance matching. The induced synergism among SiC nanowires and Co dopants endowed Co-doped SiC nanowires with strong EM wave absorption ability. The minimum reflection loss of Co-doped SiC nanowires reaches −50 dB, and the effective absorption bandwidth is 4.0 GHz with only 1.5 mm sample thickness. Thus, Co-doped SiC nanowires can be used as effective EM wave absorption materials. This study also provided a guideline for designing high-performance EM wave absorbers.

Facile Synthesis of Highly Defected Silicon Carbide Sheets for Efficient Absorption of Electromagnetic Waves

Stacking faults (SFs) within silicon carbide (SiC) are desired because these faults can enhance the electromagnetic (EM) absorption properties of the material. However, most reported SiC materials are prepared using expensive precursors possessing limited SFs. Herein, we report a facile and economical method to fabricate SiC sheets with a record-high SF density of over fourfold enhancement compared with previously reported SiC materials. The use of paper as a carbon source resulted in a 19-fold decrease in fabrication cost. The microstructure, defect structure, and EM wave absorption performance of the synthesized SiC sheets were investigated in detail. Enhancement of the SF content of the SiC sheets enabled significant interfacial dipole polarization, thereby imparting the sheets with superior EM wave absorption. SiC sheets with the maximum SF content obtained in this work revealed a minimum reflection loss of −22 dB and an effective EM wave absorption band (RL < −10 dB) covering the frequency range of 1...

Performance of barium titanate@carbon nanotube nanocomposite as an electromagnetic wave absorber

Barium titanate (BT) nanoparticles were fabricated using sol–gel method, and then immobilized onto the surface of carbon nanotubes (CNTs) to fabricate heterogeneous barium titanate@carbon nanotube (BT@CNT) nanocomposites. The electromagnetic (EM) wave absorption ability increased as the weight fraction of BT@CNT increased. The BT@CNT 30 wt.% nanocomposites with thickness of 1.1 mm showed a minimum reflection loss (R.L.) of ∼ − 37.2 dB (> 99.98% absorption) at 13.9 GHz with a response bandwidth of 1.6 GHz (12.3 ∼ 13.9 GHz), and were the best absorber when compared to similar nanocomposites with different thicknesses. The relationship between conductivity and EM wave absorption properties was also discussed. Appropriate conductivity also plays an important role to obtain optimum absorption performance. BT@CNT nanocomposites exhibited significant absorption ability, and this indicates that they can be utilized as an effective EM wave absorber material. Left: absorption performance and response bandwidth of BT@CNT 30 wt.% nanocomposites with various thicknesses. Right: TEM image of BT@CNT.

Magnesiothermic reduction of rice husk ash for electromagnetic wave adsorption

The increase in electromagnetic pollution due to the extensive exploitation of electromagnetic (EM) waves in modern technology creates correspondingly urgent need for developing effective EM wave absorbers. In this study, we carried out the magnesiothermic reduced the rice husk ash under different temperatures (400–800°C) and investigated the electromagnetic wave adsorption of the products. The EM absorbing for all samples are mainly depend on the dielectric loss, which is ascribed to the carbon and silicon carbide content. RA samples (raw rice husk ashed in air and was magesiothermic reduced in different temperatures) exhibit poor dielectric properties, whereas RN samples (raw rice husk ashed in nitrogen and was magesiothermic reduced in different temperatures) with higher content of carbon and silicon carbide display considerable higher dielectric loss values and broader bandwidth for RL<−5dB and −10dB. For RN samples, the maximum bandwidth for −5dB and −10dB decrease with carbon contents, while the optimum thickness decrease with increasing SiC content. The optimum thickness of RN400–800 for EM absorption is 1.5–2.0mm, with maximum RL of between −28.9 and −68.4dB, bandwidth of 6.7–13GHz for RL<−5dB and 3.2–6.2GHz for RL<−10dB. The magnesiothermic reduction will enhance the potential application of rice husk ash in EM wave absorption and the samples benefited from low bulk density and low thickness. With the advantages of light-weight, high EM wave absorption, low cost, RN400–800 could be promising candidates for light-weight EM wave absorption materials over many conventional EM wave absorbers.

Optimization of two-layer electromagnetic wave absorbers composed of magnetic and dielectric materials in gigahertz frequency band

Both experimentally and theoretically, a two-layer electromagnetic (EM) wave absorber exhibits the possibility of meeting the demand for effective EM wave absorbers. The first layer, made up of magnetic micpowder (MMP), has a large permeability and magnetic loss, while the second layer, comprised of MMP and nanotitanium powder, has a frequency dispersion with the parameters of permittivity and permeability to match the incidence free space over a wide frequency range. The predicted results are based on the modulus of permittivity (permeability) which obeys a logarithmic law of mixtures, and the loss tangent is related through a linear law of mixtures. A linear regression analysis performed on the data points provides constants that can be used to predict the effective parameters at different frequencies. Finally, a program is presented that computes the optimum amount of MMP in the second layer and the required thickness for each layer. The predicted results agree quite well with the measured data.