Effective Absorption Bandwidth Research Articles

Electromagnetic wave absorbing biomass kelp derived porous carbon anchored by Fe3O4 nanocomposites

Increasingly serious electromagnetic pollution problems bring the threaten for national defense security and personal health, biomass carbon materials derived absorbers have arouse widespread interest due to their green, easy accessibility, structural diversity, rich functional groups. Herein, biomass kelp derived three-dimension (3D) porous carbon/Fe3O4 (KPC/Fe3O4) nanocomposites were successfully synthesized vis KOH activation as well as in-situ growth of Fe3O4 and following pyrolysis. Attributed to multiple transmission paths for electromagnetic wave from 3D porous structure, dielectric-magnetic synergistic effect, and numerous defects in the kelp-derived carbon with polarization loss caused by heteroatom doping and interfacial polarization, KPC/Fe3O4 nanocomposites possess outstanding impedance matching and extraordinary attenuation ability. In particular, the minimum reflection loss (RLmin) value of KPC/Fe3O4-0.1 nanocomposite reaches −75.02 dB at 10.5 GHz as well as the effective absorption bandwidth (EAB, RL < -10 dB) value achieves 4.83 GHz with a thickness of 2.85 mm. Unique structures and excellent EWA performance demonstrate that KPC/Fe3O4 nanocomposites can serve as potential absorbers for military and civilian fields.

Ultrawide Spectra Camouflage Coatings from Metallic Flake Powder.

Ultrawide-spectra-compatible camouflage materials are imperative for military science and national security due to the continuous advancement of various sophisticated multispectral detectors. However, ultrawide spectra camouflage still has challenges, as the spectral requirements for different bands are disparate and even conflicting. This work demonstrates an ultrawide spectra camouflage material compatible with visible (VIS, 400-800 nm), infrared (IR, 3-5 and 8-14 μm), and microwave (S-Ku bands, 2-12 GHz). The carbon nanotubes adsorbed on porous anodic alumina/aluminum flake powder (CNTs@PAA/AFP) material for ultrawide spectra camouflage is composed of bioinspired porous alumina surface layers for low visible reflection and aluminum flake powder substrate for low infrared emissivity, while the surface of the porous alumina layers is loaded with carbon nanotubes for microwave absorption. Compared with previous low-emissivity materials, CNTs@PAA/AFP has omnidirectional low reflectance (Ravg = 0.29) and high gray scale (72%) in the visible band. Further, it exhibits low emissivity (ε3-5μm = 0.15 and ε8-14μm = 0.18) in the dual infrared atmospheric window, which reduces the infrared lock-on range by 59.6%/49.8% in the mid/far-infrared band at high temperatures (573 K). The infrared camouflage performance calculated from the radiation temperature of CNTs@PAA/AFP coatings is enhanced to over 65%, which is at least 4 times greater than that of its substrate. In addition, the CNTs@PAA/AFP coating achieves high microwave absorption (RLmin = -42.46 dB) and an effective absorption bandwidth (EAB = 7.43 GHz) in the microwave band (S-Ku bands) due to the enhancement of interfacial polarization and conductive losses. This study may introduce new insight and feasible methods for multispectral manipulation, electromagnetic signal processing, and thermal management via bioinspired structural design and fabrication.

Enhanced electromagnetic wave absorption in ultrathin cement-based composites with integrated multi-dimensional carbon materials

The challenges posed by electromagnetic waves (EMW) cause significant interference in electronic device operation, jeopardizing information security and disturbing normal biological functions, which necessitate attention. Multi-scale carbon/cement-based composites were developed for EMW absorption by integrating multi-dimensional carbon materials, including carbon nanotubes (1D), graphene (2D), and modified carbon microspheres (3D). These composites demonstrate exceptional EMW absorption capabilities, with a minimum reflection loss (RLmin) of −44.32 dB and an effective absorption bandwidth (EAB) of 3.644 GHz at X band, merely having a thickness of 1.90 mm. Furthermore, the superior EMW absorption properties of these composites are confirmed through radar cross-section (RCS) simulation and electric field distribution analysis. A small house is constructed of designed three-layer multi-scale carbon/cement-based composites in which the actual EMW reflection losses are less than –10 dB within the whole test frequency range, and these composites can effectively obstruct 5 G mobile phone signals. Therefore, multi-scale carbon/cement-based composites could be promising candidates for effectively solving the increasingly serious problem of electromagnetic radiation pollution.

Doped Porous Carbon Spheres with Controllable Vesicle Structure: Preparation and the Effects of Pore Size on Electromagnetic Wave Absorption Properties.

This work reports on the preparation of uniform vesicle-structural carbon spheres doped with heteroatoms of N, P, and S, with the pore sizes strictly controlled by the hard templates of monodisperse submicron SiO2 spheres. The uniformly doped vesicular carbon microspheres are obtained in three steps: Stöber hydrolysis for the SiO2; in situ polymerization for the immobilization; and alkaline etching after carbonization. The size of the vesicles can be easily adjusted by regulating the particle size of the submicron SiO2 spheres, which has a significant effect on its electromagnetic wave (EMW) absorption performance. Compared with microspheres with pore sizes of 180 and 480nm, when the vesicle aperture is 327nm, with only 5.5wt.% filling load and 1.9mm thickness, the material shows the best EMW absorption behavior with the effective absorption bandwidth (EAB) covers the entire Ku band (6.32GHz) and the minimum reflection loss (RLmin) of -36.10dB, suggesting the optimized pore size of the microspheres can significantly improve the overall impedance matching of the material and achieve broadband wave absorption. This work paves the way for the enhancement of EMW absorption properties of porous material by optimizing the pore size of uniform apertures while maintaining their composition.

Effects of Heat Treatment on the Electromagnetic Wave Absorption Characteristics of Resorcinol Formaldehyde Silicon Dioxide Ceramic Particles

In light of the pressing environmental and health issues stemming from electromagnetic pollution, advanced electromagnetic wave absorbing materials are urgently sought to solve these problems. The present study delved into the fabrication of the resorcinol formaldehyde (RF)/SiO2 ceramic particles using the sol–gel route. From SEM images and XRD and XPS analysis, it can be seen that the RF/SiO2 ceramic particles are successfully generated after heat treatment at 1500 °C. At room temperature, the sample treated at 1500 °C exhibited a minimum reflection loss of −47.6 dB in the range of 2–18 GHz when the matching thickness was 5.5 mm, showcasing strong attenuation capabilities. Moreover, these particles demonstrated a considerable effective electromagnetic wave absorption bandwidth of 3.14 GHz, evidencing their potential for wideband electromagnetic wave absorption. The temperature adjustment played a pivotal role in achieving optimal impedance matching. When the heat treatment temperature is increased from 800 °C to 1500 °C, the dielectric properties of the material are improved, thus achieving the best impedance matching, thereby optimizing the material’s absorption properties for specific frequency ranges, which makes it possible to customize the electromagnetic wave-absorbing characteristics to meet specific requirements across a range of applications.

Fixed-Point Atomic Regulation Engineered Low-Thickness Wideband Microwave Absorption.

Atomic doping is widely employed to fine-tune crystal structures, energy band structures, and the corresponding electrical properties. However, due to the difficulty in precisely regulating doping sites and concentrations, establishing a relationship between electricity properties and doping becomes a huge challenge. In this work, a modulation strategy on A-site cation dopant into spinel-phase metal sulfide Co9S8 lattice via Fe and Ni elements is developed to improve the microwave absorption (MA) properties. At the atomic scale, accurately controlling doped sites can introduce local lattice distortions and strain concentration. Tunned electron energy redistribution of the doped Co9S8 strengthens electron interactions, ultimately enhancing the high-frequency dielectric polarization (ɛ' from 10.5 to 12.5 at 12GHz). For the Fe-doped Co9S8, the effective absorption bandwidth (EAB) at 1.7mm increases by 5%, and the minimum reflection loss (RLmin) improves by 26% (EAB = 5.8GHz, RLmin = -46dB). The methodology of atomic-scale fixed-point doping presents a promising avenue for customizing the dielectric properties of nanomaterials, imparting invaluable insights for the design of cutting-edge high-performance microwave absorption materials.

Surfactant-induced morphology engineering in chitosan-derived carbon aerogels realizing high-efficiency absorption of electromagnetic wave

Despite the significant research advances in dielectric loss-type absorbents, developing high-efficiency electromagnetic wave (EMW) absorbents dominated by the conduction loss are still challenging due to the imbalance between impedance matching and conduction loss. In this study, for the first time, high-efficiency EMW absorption governed by the conduction loss in chitosan-derived carbon aerogels was realized through surfactant-assisted morphology modification. Electrostatic interaction and hydrogen bonding between chitosan and surfactants were ingeniously applied to induce tightly-stacked nanosheets to transform into three-dimensional (3D) interwork structure and loosely-stacked porous nanosheets, respectively, and thus the moderately enhanced conductivity converted the original EMW-transparent carbon to EMW-absorbing carbon. Benefiting from the favorable balance of impedance matching and conduction loss, the carbon aerogels with 3D interwork structure showed a broad effective absorption bandwidth (EAB) of 7.2 GHz (2.8 mm) and minimum reflection loss (RLmin) of −42.6 dB; and moreover, an ultra-wide EAB of 7.84 GHz at 2.9 mm occurred in the samples with loosen and wrinkled nanosheet structure, both outperforming most of reported carbon-based composite aerogels. This work provides a new insight for the morphology regulation and performance optimization of carbonaceous EMW absorbents.

Rice straw-inspired tunable multi-hollow channel parallel carbon fibers for enhanced electromagnetic wave absorption

The pure carbon materials are constrained in practical applications due to their inability to meet the requirements of broadband and strong absorption. To address this challenge, inspired by the parallel connection structure of hollow straw, this study successfully fabricated a multi-hollow channel parallel carbon fibers (MHCFs) structure by electrospinning and carbonization template methods. Compared with the traditional non-porous carbon fibers (CFs) structure (MHCFs-0), MHCFs-0.2 exhibit more excellent electromagnetic wave (EMW) absorption performance. It exhibits an impressive 5.59 GHz effective absorption bandwidth (EAB) at 1.8 mm. The reflection loss (RL) of MHCFs-1 reaches −52.64 dB. This remarkable enhancement in performance can be attributed to the channel structure, which can effectively introduce air, optimize impedance matching, and greatly promote polarization effects (including interface polarization and dipole polarization). It is worth noting that the integration of computer simulation technology (CST) with material structure design in this study opens up new ideas for the preparation of absorbing materials and the design of micro-nano structures, holding significant practical implications.

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.

Cross‐Scale Synergistic Manipulation of Dielectric Genes in Polymetallic Sulfides from Micropolarization to Macroconductance Toward Wide‐Band Microwave Absorption

AbstractRecently, the design and development of efficient microwave absorbents by facile engineering approaches have attracted much attention. Particularly, some unique structures caused by cross‐scale design are promising in enhancing the absorbing capability toward microwave irradiation. Herein, the cross‐scale design strategy is implemented to enhance the electromagnetic wave absorption performance of polymetallic sulfides (PMS). In PMS, the dipole polarization unit is optimized, and the distribution of electronic states is improved by doping Ti atoms; Meanwhile, the MS/M3S4 homogeneous hetero‐phases interfaces is constructed in PMS using a phase separation strategy; and the conductivity of PMS is modulated by the addition of acetylene black (ACET). The cross‐scale synergy of microwave absorption leads to a significant enhancement of the microwave absorption (MA) performance of PMS/ACET composites. The optimal reflection loss value of Ti‐LES with 10% ACET addition reaches −55.49 dB and the effective absorption bandwidth reaches 6.73 GHz. The 17.5% ACET‐conditioned Ti‐HES achieves a reflection loss of −37.2 dB at a low frequency of 4.8 GHz. This study not only provides a novel strategy for the development of new broadband MA materials but also validates a new idea for the multi‐scale synergistic optimization of MA materials.

Synthesis of flowerlike vanadium diselenide microspheres for efficient electromagnetic wave absorption

The revelation of MoS2 as an efficient electromagnetic wave (EMW) absorbing material has ratcheted up people’s attention to other transition metal dichalcogenides (TMDs). To date, extensive studies have been conducted on the semiconducting VIB-Group TMDs while research into metallic VB-Group TMDs has been relatively rare. In this work, we successfully fabricated VB-Group VSe2 microspheres through a facile one-step hydrothermal method and used them as EMW absorbers. The flowerlike VSe2 microspheres based on VSe2 nanosheets exhibited a minimum reflection loss of 46.58 dB with an effective absorption bandwidth of 4.86 GHz. The influence of material morphology, microstructure, and dielectric properties on the EMW absorption performance was systematically investigated. The hierarchically layered structure promoted dielectric loss and EMW absorption by means of multiple reflection, interfacial polarization and related relaxation, and enhanced attenuation ability. This work not only demonstrates that VSe2 is potentially a high-efficiency single component EMW absorber, but also provides fresh insights into exploration on the EMW loss mechanisms of the metallic TMD-based absorbing materials.

Mesoporous silica@polypyrrole and its epoxy composites with ultra-broadband electromagnetic wave absorption properties

Composite of powders with exceptional electromagnetic wave absorption (EMA) properties with resins is an important tactic for preparing electromagnetic wave (EMW) stealth composites. However, high expenditure, low yield and the complex synthesis of these powders constrain their utilization in composite materials. Moreover, composite materials need greater thickness to fulfill EMA requirements. This work reported a facilely producible absorber, mesoporous Silica@Polypyrrole (MSU-J@PPy), which exhibits enhanced EMA performance. The polymerization of PPy in the connected three-dimensional pores as well as on the surface of MSU-J led to the creation of conductive network thereby enhancing the conductive loss. MSU-J contributes to the lightweighting and impedance matching and promotes the formation of a non-homogeneous interface. By varying the ratio of PPy to MSU-J, precise control of EMA was realized. When the proportion of PPy to MSU-J by weight is 1.5:1, the reflection loss (RL) of MSU-J@PPy reaches an impressive −46.44 dB at 1.9 mm. The effective absorption bandwidth (EAB) is 6.08 GHz (11.92–18 GHz) at 2.1 mm thickness of the sample. Further, MSU-J@PPy and carboxylated multi-walled carbon nanotubes (cMWCNTs) was composited with epoxy resin (EP) to develop a wave-absorbing composites MSU-J@PPy/cMWCNTs/EP with ultra-broadband absorption properties and outstanding mechanical characteristics. At a thickness of 1.7 mm, the composite can effectively absorb EMW in the entire Ku band, and effective absorption across the 5.4–18 GHz range can be attained through changing the matching thickness. This work offers a novel approach for developing cost-effective, easily synthesized, and high-yield EMW absorbers, as well as their application in absorber composite materials.

MXene/cobalt ferrite/carbon materials based composites for efficient microwave absorption

In the present study, cobalt ferrite (CF) nanoparticles were in-situ grown on MXene/carbon-based materials (activated carbon (AC), MWCNT, and GO) to develop composites via facile hydrothermal route. The MXene/CF/MWCNTs composite (FMCNT4) achieved an excellent maximum reflection loss (RLmax) of −67.04 dB at 16.24 GHz & a thickness of 5.94 mm, whereas at the thickness of 5.86 mm, the FMCNT4 obtained a maximum effective absorption bandwidth (EAB, RL < −10 dB) of 2.73 GHz. On the other hand, replacing MWCNTs with AC in the composite (FMAC4) showed RLmax of −46.52 dB at 18 GHz and 5.1 mm thickness, it also got an EAB of 2.54 GHz at 5.5 mm thickness. The MXene/CF/GO composite (FMGO5) obtained RLmax = −17.31 @ 17.12 GHz & 6 mm. The composite having MWCNTs showed the best performance, and the reason for this remarkable MW absorption performance originated from the high impedance matching followed by dielectric polarization and magnetic losses in the composite. The formation of multiple heterointerfaces between MXene, CF, and MWCNTs enhanced the interfacial polarization, whereas the conducting MXene and MWCNTs also contributed to conduction polarization. Thus, the present investigation showcases FMCNT as an excellent synergetic nanocomposite for MW absorption applications.

Preparation of high-performance bitumen carbon-based microwave absorbing materials from different coal bitumens toward efficient treatment of industrial waste bitumen

The increasing development of communication technology and electromagnetic pollution have accelerated the research and optimization of electromagnetic microwave absorbing materials. There are few studies and reports on the creation electromagnetic microwave absorbing materials from industrial waste, despite the abundance and promise of research preparing of microwave absorbing materials utilizing sustainable resources from biomass. Herein, we prepared carbon-based microwave absorbing materials GCB-800, HTCB-800, and CDLB-800 using three different industrial solid waste bitumens, namely, coal direct liquefaction bitumen, high-temperature coal bitumen, and globular coal bitumen, as raw materials by using the thermal activation method. Due to the excellent porous carbon skeleton structure and the Fe2O3 contained in its internal ash after the heat treatment, which enhances the internal dielectric properties, the CDLB-800 was found to perform very well at the filler amount of 10 wt% obtained minimum reflection loss (RLmin) is −52.41 dB at 10 wt% filler and matched thickness d = 2.1 mm, and the effective absorption bandwidth (EAB) is 4.88GHz, with 87.14% absorption for X-band in the 2-18GHz. This work not only promotes the development of the comprehensive utilization of solid waste in this field, effectively reduces the burden of solid waste on the environment, but also points out the direction for the development of microwave absorbing materials in the future.

Integrating Sulfur Doping with a Multi-Heterointerface Fe7S8/NiS@C Composite for Wideband Microwave Absorption.

Heterointerface engineering is presently considered a valuable strategy for enhancing the microwave absorption (MA) properties of materials via compositional modification and structural design. In this study, a sulfur-doped multi-interfacial composite (Fe7S8/NiS@C) coated with NiFe-layered double hydroxides (LDHs) is successfully prepared using a hydrothermal method and post-high-temperature vulcanization. When assembled into twisted surfaces, the NiFe-LDH nanosheets exhibit porous morphologies, improving impedance matching, and microwave scattering. Sulfur doping in composites generates heterointerfaces, numerous sulfur vacancies, and lattice defects, which facilitate the polarization process to enhance MA. Owing to the controllable heterointerface design, the unique porous structure induced multiple heterointerfaces, numerous vacancies, and defects, endowing the Fe7S8/NiS@C composite with an enhanced MA capability. In particular, the minimum reflection loss (RLmin) value reached -58.1dB at 15.8GHz at a thickness of 2.1mm, and a broad effective absorption bandwidth (EAB) value of 7.3GHz is achieved at 2.5mm. Therefore, the Fe7S8/NiS@C composite exhibits remarkable potential as a high-efficiency MA material owing to the synergistic effects of the polarization processes, multiple scatterings, porous structures, and impedance matching.

Surface engineering strategy for MXene to tailor electromagnetic wave absorption performance

The emerging two-dimensional material, Ti3C2Tx MXene, has attracted significant attention in the realm of electromagnetic wave absorption owing to its exceptional inherent conductivity and distinctive microstructure. However, similar to other conductive materials, MXene encounters the challenge of impedance mismatch, thereby impeding the electromagnetic wave absorption capability in single-component MXene materials. In this study, a molten chlorine-salt method was employed to gain MXene samples with varying surface-chlorine/oxygen (Cl/O) ratios by surface engineering. Notably, among these samples, Cl/Ni-MX-6 exhibited an impressive minimum reflection loss value of −45.72 dB (1.6 mm) and an effective absorption bandwidth of 3.44 GHz (1.3 mm). This study revealed that increasing the etchant content enhances the delamination effect of MXene and leads to adjust Cl/O ratio. Importantly, the modulation of −Cl/O surface functional groups can limit the electronic conductivity, while the number and species of different kinds of surface dipoles will control the polarization effect, ultimately optimizing the electromagnetic wave absorption performance of pure MXene. These insights contribute to ongoing efforts aimed at enhancing the performance of MXene-based materials in the field of electromagnetic wave absorption as well as get a better understanding of the electromagnetic loss mechanism.

Biomimetic artificial nacre-like microfiber of Co/C modified cellulose nanofiber/Ti3C2Tx MXene with efficient microwave absorption

Although considerable efforts have been made in the fabrication of MXene-based composites for microwave absorption (MA), there is a great challenge to assemble MXene into regularly arranged microfibers prepared by wet-spinning technique for application in the field of MA due to insufficient interlayer interactions between Ti3C2Tx flakes. Heterogeneous interface design by optimizing material components to construct ingenious microstructure is crucial for efficient microwave absorbers. Herein, artificial nacre-like supramolecular microfibers of Co/C modified cellulose nanofiber/Ti3C2Tx MXene (Co/C/CNF/Ti3C2Tx) with plenty of heterogeneous interfaces were prepared by a simple wet-spinning technology through a self-assembly process induced by hydrogen bonding interactions between CNF and Ti3C2Tx. The artificial nacre-like microfibers with layered structure possess abundant heterogeneous interfaces, which facilitate multiple reflections/scattering of electromagnetic waves (EMW) between these interfaces, and at the same time promote interfacial and dipole polarization. The introduction of magnetic Co/C nanoparticles not only offer additional magnetic loss ability and improved impedance matching, but also enhance conductivity loss and polarization loss. Benefiting from these advantages, Co/C/CNF/Ti3C2Tx (1:1:1) fiber exhibits superior MA performance with a minimum reflection loss (RLmin) of up to −62.32 dB (>99.9999 % energy absorption) and a broad effective absorption bandwidth (EAB) of 5.86 GHz. The work provides a promising method for the preparation of biomimetic artificial nacre-like MXene-based microfibers with efficient MA performance, which is expected to be applied in the field of flexible wearable electromagnetic protection.

A competitive strategy toward 1 T/2H MoS2 to balance impedance for optimizing electromagnetic wave absorption

Interface engineering and phase engineering play crucial roles in enhancing the design and development of advanced electromagnetic wave (EMW) absorbers. However, there is a lack of focus on designing phase structures and interfaces from a microscopic perspective to adjust impedance matching and EMW absorption. This study introduced a competitive strategy involving 1 T/2H MoS2. The phase structure and composition of MoS2 were controlled using a microwave hydrothermal method. By creating a diverse phase interface within the material in the form of 1 T/2H, a balance between conduction loss and polarization loss was achieved, leading to improved EMW absorption through enhanced impedance matching. The results indicated that the incorporation of the 1 T phase boosted the electron transfer capability of MoS2, increasing conduction loss. The 1 T/2H phase interface enhanced interface polarization, thereby amplifying polarization loss. At a thickness of 2.8 mm, the absorber demonstrated a minimum reflection loss of −64.9 dB and an effective absorption bandwidth of 4.6 GHz. In far-field conditions, the maximum radar cross-section (RCS) of the 1 T/2H phase MoS2 nanoflowers was −27.5 dBm2. This study elucidates the relationship between 1 T/2H phase MoS2 content and phase interfaces with impedance matching, offering a novel approach for developing high-performance MoS2-based EMW absorbing materials.

MOFs-derived 3D flower-like Y2O3/C microspheres with efficient electromagnetic wave absorption properties

Y2O3 has emerged as a promising material for electromagnetic wave (EMW) absorption due to its excellent dielectric properties. However, the inherent insulating nature and single loss mechanism limit its absorption performance. Research on the microstructure modulation and component regulation of Y2O3-based absorbers remains relatively unexplored. In this work, Y2O3/C composites with flower-like architectures were synthesized for the first time via a metal-organic framework (MOFs) templating method. The effects of pyrolysis temperature on the microstructure, phase composition, and EMW absorption performance of the Y2O3/C composites were systematically investigated. At a pyrolysis temperature of 800 °C, the flower-like Y2O3/C microsphere exhibited optimal EMW absorption performance. The minimum reflection loss (RL) of pristine Y2O3 was only −4.75 dB, while the Y2O3/C composite achieved a minimum RL of −51.77 dB and a maximum effective absorption bandwidth of 4.32 GHz. Moreover, by simply adjusting the matching thickness, the optimal sample exhibited strong absorption (RL < −30 dB) over a wide frequency range of 4–18 GHz. The incorporation of carbon effectively neutralized the insulating nature of Y2O3, thereby optimizing the impedance matching. The synergistic effects of multiple loss mechanisms, including polarization loss, resistance loss, and interfacial polarization, facilitated substantial EMW attenuation. This study provides a promising strategy for the design and fabrication of high-performance rare-earth oxide EMW absorbers with tunable morphologies and properties.

Ultrabroad electromagnetic absorbing core-shell SiC@SiO2 nanocomposites derived from in situ oxidation SiC whiskers

The amazing developing electromagnetic technology has brought severe challenges to the military and civilian fields, efficient electromagnetic wave absorption (EWA) materials with high-temperature resistance are urgent needed. In this paper, SiC@SiO2 nanocomposites with unique core-shell structures were successfully prepared using a straightforward method by in situ oxidation SiC whiskers. By regulating the sintering temperature and oxidation time, the microstructures and EWA performance of SiC@SiO2 nanocomposites were explored. The results show that the core-shell SiC@SiO2 nanocomposites obtained after sintering at 1200 ℃ for 0.5 h exhibits the best EWA performance, where the minimum reflection loss (RLmin) of −36.80 dB at the thickness of 2.68 mm and the effective absorption bandwidth (RL<-10 dB, EAB) of 9.85 GHz at a matching thickness of 4.24 mm. Specially, the EAB can reach up 10.98 GHz with the filling content of only 10%, which surpasses most SiC-based absorbers. The ultrabroad absorbing bandwidth can be attributed to that the unique core-shell structures of SiC whiskers with in-situ grown SiO2 layers on the surface provide good impedance matching, multiple reflection and scattering and interface polarization effects. This work provides a new strategy for the design of high temperature resistant absorbing materials.