Excellent Microwave Absorption Properties Research Articles

Optimizing the electromagnetic wave absorption properties of core-shell Fe/FeN/Fe3C@GN nanoparticles by low-temperature NH3 plasma

Surface modification via low-temperature plasma has an extensive application prospect in different engineering fields due to its comprehensive merits in facilitating the introduction of functional groups and creating more heterogeneous interfaces. Herein, a simple high-temperature plasma method is developed to get novel multiple-phase nanocomposites of core-shell Fe/FeN/Fe3C@GN nanoparticles with bifunctional characteristics of microwave absorption (MA) and anti-corrosion. And then, we further investigate the MA properties of Fe/FeN/Fe3C@GN nanoparticles after low-temperature NH3 plasma etching. It is found that surface modification of Fe/FeN/Fe3C@GN nanoparticles can generate remarkable changes in specific surface areas, Raman features and MA properties of these nanocomposites. The Fe/FeN/Fe3C@GN nanoparticles after NH3 plasma etching possess excellent MA properties with an optimal reflection loss (RL) of −51.0 dB at an ultra-thin thickness of 1.9 mm with a low filling content of 30 wt% and the corresponding effective absorption bandwidth (EAB < −10 dB) up to 4.7 GHz (13.3–18.0 GHz). The fascinating MA properties of etched Fe/FeN/Fe3C@GN nanoparticles may be attributed to the cooperative effect of several points: (i) The NH3 plasma etch introduces a large number of polar functional groups, which can be regarded as the polarization center to produce more polarization loss; (ii) The appropriate dielectric loss and impedance matching achieve a good balance, and the abundant heterogeneous interface significantly enhances the polarization relaxation loss; (iii) The existence of hetero-nanostructure further improves the multiple reflections and scattering of the propagating microwaves. In addition, this work provides a new strategy for the design and fabrication of core-shell MA materials.

In Situ Synthesis of an Epoxy Resin Microwave Absorption Coating with Anti-Ultraviolet Aging Effects

A nanoparticle-anchored three-dimensional microsphere flower-structured layered double hydroxide (LDH) material with Fe3O4 particles was successfully prepared using simple hydrothermal and hot solvent methods. Micro-nanostructured Fe3O4@LDHs (SLF) composites balance microwave absorption, corrosion protection, and UV aging resistance. The minimum reflection loss value of SLF is −35.75 dB at 14.16 GHz, when the absorber thickness is 8 mm, and the absorption bandwidth at this frequency is up to 2.56 GHz for RL values less than −10 dB, while the LL is only 1 GHz. The SLF /EP coating has not only excellent microwave absorption performance but also excellent corrosion and UV aging resistance performance. The coating still has some anti-corrosion effect after 10 d of immersion. This work is intended as a reference for the development of new coatings with excellent microwave absorption properties as well as corrosion and UV aging resistance for wind turbine tower barrels (seaside wind power generation equipment) surfaces.

Excellent microwave absorption property of 3D printed SiCN matrix metamaterial

The combination of 3D printing, polymer derived ceramics, and electromagnetic wave (EMW) absorption metamaterials is particularly useful for spacecraft stealth in extreme environments and is gradually gaining significant interest. While the 3D printing of SiOC has been extensively researched, the high temperature stability and mechanical performance of SiOC are not as favorable as SiCN. However, it remains challenging to prepare SiCN metamaterials with both high mechanical and microwave absorption properties by 3D printing. Herein, we demonstrate a SiCN EMW absorption metamaterial with high mechanical properties using digital light processing 3D printing, which achieves a minimum reflection loss of −31.01 dB (99.9 % absorption), and the widest effective absorption bandwidth covers the entire X-band from 8.2 to 12.4 GHz. And the EMW absorption performance can be adjusted based on the size of the unit structure.

Cation Bimetallic MOF Anchored Carbon Fiber for Highly Efficient Microwave Absorption.

Carbon fiber (CF) is a potential microwave absorption (MA) material due to the strong dielectric loss. Nevertheless, owing to the high conductivity, poor impedance matching of carbon-based materials results in limited MA performance. How to solve this problem and achieve excellent MA performance remains a principal challenge. Herein, taking full advantage of CF and excellent impedance matching of bimetallic metal-organic frameworks (MOF)derivatives layer, an excellent microwave absorber based on micron-scale 1D CF and NiCoMOF (CF@NiCoMOF-800)is developed. After adjusting the oxygen vacancies of the bimetallic MOF, the resultant microwave absorber presented excellent MA properties including the minimum reflection loss (RLmin ) of -80.63dB and wide effective absorption bandwidth (EAB) of 8.01GHz when its mass percent is only 5wt.% and the thickness is 2.59mm. Simultaneously, the mechanical properties of the epoxy resin (EP)-based coating with this microwave absorber are effectively improved. The hardness (H), elastic modulus (E), bending strength, and compressive strength of CF@NiCoMOF-800/EP coating are 334MPa, 5.56GPa, 82.2MPa, and 135.8MPa, which is 38%, 15%, 106% and 53% higher than EP coating. This work provides a promising solution for carbon materials achieving excellent MA properties and mechanical properties.

One-step preparation of sea urchin-like conducting polypyrrole-modified porous carbonyl iron powders with excellent microwave absorption properties

Carbonyl iron powder (CIP) is a common microwave absorber frequently utilized to prepare microwave-absorbing materials. However, it exhibits only magnetic loss and no dielectric loss, which inevitably affects its wave-absorbing performance. Here, porous carbonyl iron powder (p-CIP) modified with conductive polypyrrole (PPy) was successfully prepared by one-step chemical etching and in-situ polymerization and then utilized to fabricate epoxy composites with high microwave absorption intensity. The scanning electron microscopy images revealed that conductive PPy was encapsulated on the surface of p-CIP. The reflection loss of the P-200 sample is −41.2 dB at 2.2 mm thickness. Reduction of the sample thickness to 1.8 mm resulted in a still acceptable reflection loss of −35.5 dB. Moreover, the effective absorption bandwidth widened to approximately 6.75 GHz (10.55–17.3 GHz). This provides a valuable approach for the development of microwave-absorbing materials with high absorption capacity.

Lightweight zirconium modified carbon–carbon composites with excellent microwave absorption and mechanical properties

With the rapid development of space technology, multi-functional materials with advantages such as heat insulation, lightweight, and electromagnetic (EM) wave absorption have gained broad application prospects. Since porous carbon fiber reinforced carbon (C/C) composites often have lightweight and high heat insulation properties, improving their mechanical and electromagnetic wave absorbing properties will significantly expand their application. In this study, a new kind of zirconium-modified C/C (Zr-C/C) composites prepared by polymer infiltration and pyrolysis using zirconium-modified phenolic resin is presented. By adjusting the content of Zr, the compressive strengths of the composites are increased up to 48% compared with the composites without Zr, while the thermal insulation properties are little changed. The incorporation of zirconium can make the composites exhibit better microwave absorption performance to some extent, and Zr-C/C composites with 10% zirconium have the best microwave absorption performance among all the samples. The excellent electromagnetic wave absorption performance of Zr-C/C composites is attributed to the enhanced interfacial polarization effect and the improved electrical conductivities of the material due to its internal carbon microsphere structure. Multi-functional Zr-C/C composites that combine lightweight, high thermal insulation, high compressive strength, and high electromagnetic wave absorption have obvious applications in fields such as stealth aircraft. Therefore, this work provides a new way to prepare multi-functional materials.

Magnetic vortex configuration in Fe3O4 nanorings/nanotubes for aspect ratio and magnetic orientation regulated microwave absorption

Morphological structure can greatly affect the magnetic domain of magnetic materials, which plays a significant role on regulating the magnetic characteristics and electromagnetic properties. Herein, Fe3O4 nanorings/nanotubes with adjustable aspect ratio were fabricated through a hydrothermal route followed by reduction annealing treatment. The magnetic flux distributions in radial and axial direction were characterized by electron holography, suggesting that the Fe3O4 nanorings/nanotubes show magnetic vortex structure. The magnetic vortex-domain structure is favored to break the Snoek’s limit of Fe3O4, improving the high-frequency permeability and boosting the natural resonance band to 1 ∼ 10 GHz. Meanwhile the complex permittivity is highly sensitive to the aspect ratio. The Fe3O4 nanorings/nanotubes perform excellent comprehensive microwave absorption properties, owing to the special magnetic vortex structure, tunable complex permittivity, big complex permeability, large magnetization and high natural resonance. The Fe3O4 nanorings with the smallest aspect ratio show a minimum reflection loss (RL) value of −47.9 dB at 2.6 mm and EAB of 4 GHz at 3 mm. Besides, rotational orientation by an external magnetic field can cause the parallel arrangement of nanorings/nanotubes, which can increase both the complex permittivity and broad the resonance band. Rotational orientation can realize effective absorption efficiency at a broader frequency range with a thinner thickness, further improving the comprehensive microwave absorption. These findings not only suggest that designing particular magnetic-domain structures by morphologies can break the Snoek’s limit of magnetic materials, but also demonstrate that aspect ratio and magnetic field-assisted rotational orientation is promising ways to regulate the electromagnetic parameters, resulting in high-performance microwave absorption.

Regulation Dipole Moments of N-Doped Graphene Coordinated with FePc Toward Highly Efficient Microwave Absorption Performance in C Band.

The development of composites with highly efficient microwave absorption (MA) performance deeply depends on polarization loss, which can be induced by charge redistribution. Considering the fact that polarization centers can be easily obtained in graphene, herein, iron phthalocyanine (FePc) is used as polarization site to coordinate with nitrogen-doped graphene (FePc/N-rGO) to optimize MA performance comprehensively. The factors influencing MA properties focus on the interaction between FePc and N-rGO, and the change of dipole moments. The density functional theory (DFT) results demonstrated that FePc has strong interaction with N defect sites in graphene. The charge loss for FePc and charge accumulation for N-rGO occurred, leading to great increase of dipole moment, and the increased dipole moment can be acted as a descriptor to evaluate the enhanced polarization loss. Due to high charge redistribution capacity of N defect sites and FePc polarization centers, the FePc/N-rGO showed excellent MA properties in C band, and the minimum reflection loss value can reach -49.3dB at 5.4GHz with thickness of 3.8mm. In addition, the fabric loaded with FePc/N-rGO showed good heat dissipation property. This work opens the door to the development of MA performance bound to polarization site with dipole moment.

The honeycomb mesh structure derived from mangosteen shells with excellent microwave absorption properties

In this study, we successfully created a microwave absorbing materials with honeycomb network structured using mangosteen shells. This was achieved by regulating the ratio of KOH to precursors during a one-step carbonization process. The morphological optimization of biomass carbon was facilitated by this research, which also investigated its microwave absorption performance. Samples obtained at 700 °C using a 1:2 activated agent ratio showed superior performance in terms of microwave absorption. At a thickness of 1.94 mm, the optimal sample exhibits a minimum reflection loss of −52.7 dB and a maximum effective absorption bandwidth of 2.32 GHz. The findings demonstrate that the activating impact of KOH can significantly enhance the pore structure of carbon materials, hence improving their microwave absorption performance. This study offers a cost-efficient and effective approach to produce lightweight and high-performing microwave absorbing materials.

Influence of Bi doping on the structure and electromagnetic wave absorption for LaFeO3 perovskite

LaFeO3 perovskite has possessed great potential in the field of microwave absorption considering its outstanding dielectric and magnetic properties. In this work, Bi-doped LaFeO3 powders (BLFO) were prepared by a simple solid state reaction method. The results have demonstrated that the crystalline of LaFeO3 and the lattice oxygen are increased with the additionally introduced Bi. As a result, the samples could exhibit the strongest microwave absorption with the minimum reflection loss (RLmin) of −39.48 dB and the effective absorption band (EAB) of 3.63 GHz (10.28–13.91 GHz) at a filling ratio of 60 wt%. The excellent microwave absorption properties are ascribed to the enhanced conductive loss, polarization relaxation and the co-existed magnetic loss. Moreover, the optimum sample exhibits the radar cross-section values below −10 dBm2 across a wide angular range of −90° to 90° with a thickness of 2.5 mm. Therefore, this work opens up a feasible and effective way for modulating the electromagnetic properties of perovskite materials as potential microwave absorbents.

Multifunctional Carbon Fiber Reinforced C/SiOC Aerogel Composites for Efficient Electromagnetic Wave Absorption, Thermal Insulation, and Flame Retardancy.

Carbon fiber composites have great application prospects as a potential electromagnetic (EM) wave-absorbing material, yet it remains extremely challenging to integrate multiple functions of EM wave absorption, mechanical strength, thermal insulation, and flame retardancy. Herein, a novel carbon fiber reinforced C/SiOC aerogel (CF/CS) composite is successfully prepared by sol-gel impregnation combined with an ambient drying process for the first time. The density of the obtained CF/CS composites can be controlled just by changing sol-gel impregnation cycles (original carbon fiber felt (S0), and samples with one (S1) and two (S2) impregnation cycles are 0.249, 0.324, and 0.402 g cm-3, respectively), allowing for efficient tuning of their properties. Remarkably, S2 displays excellent microwave absorption properties, with an optimal reflection loss of -65.45dB, which is significantly improved than S0 (-10.90dB). Simultaneously, compared with S0 (0.75 and 0.30MPa in the x/y and z directions), the mechanical performance of S2 is dramatically improved with a maximum compressive strength of 10.37 and 4.93MPa in the x/y and z directions, respectively. Moreover, CF/CS composites show superior thermal insulation capability than S0 and obtain good flame-retardant properties. This work provides valuable guidance and inspiration for the development of multifunctional EM wave absorbers.

A novel rGO-ZnFe2O4 hollow microsphere composite with excellent microwave absorption properties

In order to develop lightweight, efficient and broadband microwave absorbing materials, rGO-ZnFe2O4 hollow microsphere composites were prepared by the solution method in this paper. The effects of reduced graphene oxide (rGO) content on the microstructure of hollow microspheres and the microwave absorption properties of the material were studied. rGO micropowders and ZnFe2O4(ZFO) particles are uniformly distributed on the hollow microspheres. The rich porous hollow structure is conducive to the multiple reflection and scattering of electromagnetic microwaves. This structure and distribution state enable the composite material to have good impedance and form a synergistic effect of multiple absorption effects. The results show that the minimum reflection loss (RLmin) is −28.83 dB and the effective absorption bandwidth(EAB) is 5.92 GHz (11.04∼16.96 GHz) when the thickness is 2.00 mm and the rGO is 6.3 wt.%. The Radar scattering cross section(RCS) results show that the RCS values of the samples with the rGO is 6.3 wt.% are mostly below −20 dBm2 in the range of microwave incidence angle of −90°< Theta < 90°, which indicates the composites has wide-angle microwave absorption ability. This study provides a new approach to the design and preparation of efficient and lightweight electromagnetic microwave absorbing materials.

Well-matched PANI@FePO4@FeSi hybrid composite with excellent microwave absorption property

PANI@FePO4@FeSi composites were prepared by one-pot synthesis. The PANI@FePO4 coating layer can effectively enhance magnetic loss, dielectric losses, and improve impedance matching by reduce the skin effect. The optimized reflection loss (RL) of the composites is −54 dB at 15.76 GHz with the absorption bandwidth (RL<−10 dB) of 2.7 GHz (14.3−17 GHz).Density functional theory (DFT) and ANSYS High-Frequency Structure Simulator (HFSS) analysis results suggest that destruction of local microstructural symmetry and inducing additional electric dipoles at the interface of each component. The density of state (DOS) of p orbital near the Fermi level decreases. Thus, dipole oscillation and polarization loss get enhanced under the external electromagnetic field. This work provides an avenue for designing new microwave absorbers.

Zn-MOF-derived hierarchical carbon nanorods superstructures with tunable microwave absorption properties

Nanometer/micron scale multilevel superstructure has the potential to be a good microwave absorbing (MWA) materials owning to its large specific surface area and good electrical conductivity, but assemble 1D rod/wire-like into a three-dimensional (3D) hierarchical superstructure with a large controllable radius of curvature spherical tissue, is still a challenge. Here we demonstrate a self-templated strategy through pyrolysis the modulator (urea) modified Zn-MOF 74 to obtain the spherical superstructure of carbon nanorods (SSC). The dielectric constant of SSC absorbers regulated by the amount of urea added. A moderate amount of urea will endow the material a high specific surface area and defect-induced mesopore, thus the excellent MWA properties. The prepared SSC-U2 has a good MWA performance that the minimum reflection loss (RL, min) can reach -54 dB only when the thickness is 2.1 mm. This work designs a new strategy to prepare the 3D hierarchical superstructure carbon by using MOFs and offers insight into the relationship between morphology, surface area and dielectric constant of absorber, promoting rational design of highly efficient microwave absorber.

Confined In-Situ Encapsulation of Co/C Composites with Increased Heterogeneous Interface Polarization for Enhanced Electromagnetic Performance.

It is an urgent problem to realize reliable microwave absorption materials (MAMs) with low density. To address this issue, a series of controlled experiments w ere carried out, which indicated that the tubular structure enables excellent microwave absorption properties with a lower powder filling rate. This performance is attributable to the combined dielectric and magnetic loss mechanisms provided by Co/C and the interface polarization facilitated by multiple heterogeneous interfaces. Particularly, Co@C nanotubes, benefiting from the enhanced heterointerface polarization due to their abundant specific surface area and the reduced electron migration barrier induced by their 1D stacked structure, effectively achieved a dual enhancement of dielectric loss and polarization loss at lower powder filling ratios. Furthermore, the magnetic coupling effect of magnetic nanoparticle arrays in tubular structures is demonstrated by micromagnetic simulation, which have been few reported elsewhere. These propertied enable Co@C nanotubes to achieve minimum reflection lossand maximum effective absorption broadband values of 61.0dB and 5.5GHz, respectively, with a powder filling ratio of 20wt% and a thickness of 1.94mm. This study reveals the significance of designing 1D structures in reducing powder filling ratio and matching thickness, providing valuable insights for developing MAMs with different microstructures.

A facile and large-scale route to prepare nitrogen/oxygen (N/O) co-doped two-dimensional carbon nanomesh with excellent microwave absorption properties

Two-dimensional porous carbon materials have been considered good candidates for developing lightweight microwave absorbers because of their low density and tunable dielectric constant. However, large-scale synthesis, with precise control of the microstructure, by a simple method, remains is still a great challenging. Herein, a two-dimensional N/O co-doped carbon nanomesh (NOCN) was prepared via large-scale route by simple carbonization of analogue polyurea (PU) nanosheet consisted of p-phenyldiisocyanate and urea, and the graphitization degree, porous structure, sheet size and the heteroatom doping content could be easily adjusted by controlling carbonization temperature. Thus, the electromagnetic parameter and the corresponding microwave absorption can be regulated. When the carbonization temperature was 900 °C (NOCN-900), the obtained sample exhibited the best microwave absorption performance, and the reflection loss (RL) value was −54.2 dB with an effective absorption bandwidth (EAB) of 7.44 GHz at a thickness of 2.3 under fill loading of only 5 wt%. The facile and large-scale synthesis route combined with excellent performance makes NOCN-900 to be a great promising candidate for practical application.

GR-Fe3O4/PLA 3D printing composite materials with excellent microwave absorption properties

In this work, composite microspheres were formed by integrating graphene (GR) and Fe3O4 into an ethylcellulose matrix via an emulsion emulsification reaction. Composite wires were fabricated using a melt extrusion process and composite samples were subsequently prepared via a melt molding method. A systematic study was conducted to investigate the absorption performance of GR-Fe3O4/PLA (Polylactic acid) composite materials. The findings revealed that the optimal microwave absorption performance was achieved when the graphene content was 5.6 wt% and the Fe3O4 content was 11.1 wt%. The maximum reflection loss was − 51.13 dB at a thickness of 2.65 mm. The maximum absorption bandwidth was 4.16 GHz, and the effective radar interception cross-section was reduced to − 42.7 dBm2. The excellent performance of GR-Fe3O4/PLA composite material can be attributed to good impedance matching and the synergistic effect of conductive loss, dipole polarization, interface polarization, and eddy current loss. Then the contribution of conductive loss and polarization loss to the absorption performance was explored. This work provides a novel approach to advance the design and development of functional materials for efficient electromagnetic absorption, providing valuable insights into the development of efficient, lightweight microwave absorbing material.

Fabrication of multiple core-shell structures MnO@HsGDY@NC@HsGDY hybrid nanofibers for enhanced microwave absorption

Optimizing the structure and composition of emerging materials to produce efficient absorbers are one strategy for addressing electromagnetic pollution and radar stealth. For the first time, hydrogen-substituted graphdiyne (HsGDY) is used as a functional component for the preparation of microwave-absorbing materials in this paper. By using MnO2 nanowires as template and sequentially coating HsGDY, polydopamine (PDA) and HsGDY shell layers, MnO2@HsGDY@PDA@HsGDY nanowire precursors are obtained. The one-dimensional (1D) nanowires combine the advantages of multicomponent composite, multiple core-shell structures. After calcination, 1D microwave absorption absorber MnO@HsGDY@NC@HsGDY with multi-layer and core-shell structures is produced. The high conductivity of HsGDY enhances the material's dielectric loss, and the multiple heterogeneous interfaces in the material structure cause interface polarization, resulting in the excellent microwave absorption properties. MnO@HsGDY@NC@HsGDY exhibits the advantages of low filler content, thin matching thickness, strong microwave absorption capacity and wide effective absorption band (EAB). The minimum reflection loss (RLmin) can reach −68.57 dB@13.8 GHz@2.4 mm, and the EAB is 6.7 GHz as the filler content is 11 %. This work enriches the types of 1D materials and absorbers, expands the application fields of HsGDY, and provides a reference for the design and preparation of absorbers.

Dense NiCo2 O4 Nanoneedles Grown on Carbon Foam Showing Excellent Electrochemical and Microwave Absorption Properties.

Electromagnetic pollution could harm sensitive electronic equipment due to the rising use of electronic devices and communication infrastructure. The supercapacitor's electrochemical performance should be enhanced, and electromagnetic damage should be prevented. This study proposes NiCo2 O4 /CF composites for supercapacitors and microwave absorption. They are made by combining hydrothermal and annealing processes. Dense NiCo2 O4 nanoneedles were uniformly grown on the outer layer of carbon foam (CF) as a growth skeleton, preventing the agglomeration of NiCo2 O4 . The composite had a specific capacitance of 537.5 F/g at 1 A/g. When the current density was set to 1 A/g, the supercapacitor that used NiCo2 O4 /CF as the cathode had a specific capacitance of 70.7 F/g, and when the current density was increased to 10 A/g, the original specific capacitance of 87.2 % could still be maintained after 5000 charge-discharge cycles. At a power density of 3695.5 W/kg, an energy density of 22.1 Wh/kg could be maintained. Furthermore, we performed a microwave absorption test and determined its reflection loss curve for various sample thicknesses. Recombination enhanced the composite material's microwave absorption capability by greatly reducing the dielectric loss and the magnetic loss.

Synthesis of ZSM-5/FexOy@C/Ni microspheres for enhanced electromagnetic wave absorption

Reasonable microstructure design and composition of absorbing materials are essential to improve absorbing properties. In this paper, ZSM-5/FexOy@C/Ni composite absorbing material with double core-shell structure was prepared by hydrothermal method and sol-gel method. The composite's structure, morphology, chemical composition, and magnetic properties were studied. The surface and C layer of ZSM-5 were densely covered with FexOy and Ni nanoparticles, respectively. At the same time, the uniform distribution of magnetic units can effectively improve the spatial distribution of magnetism. It was worth noting that the optimized composites had excellent microwave absorption properties. When the sample thickness was 2.5 mm, the minimum reflection loss of the sample could reach −21.4 dB, and the maximum effective bandwidth could reach 5.4 GHz. It was found that by changing the carbon layer's thickness, the prepared sample's absorption property could be adjusted to achieve the best impedance matching. The superior electromagnetic absorption performance of ZSM-5/FexOy@C/Ni composite microspheres was due to the synergistic effect of dielectric loss and magnetic loss and the enhanced porous core-shell interface effect. These results indicated that the composite could be used as a promising new type of high-performance absorbing material.