Synthesis of carbon-coated cobalt ferrite core-shell structure composite:A method for enhancing electromagnetic wave absorption properties by adjusting impedance matching

Cobalt ferrite has problems such as poor impedance matching and high density,which results in unsatisfactory electromagnetic wave(EMW)absorption performance.In this study,the CoFe_(2)O_(4)@C core-shell structure composite was synthesized by a two-step hydrothermal method.X-ray diffraction,transmission electron microscopy,Fourier transform infrared spectroscopy,thermogravimetric analysis,and vector network analysis et al.were used to test the structure and EMW absorption properties of CoFe_(2)O_(4)@C composite.The results show that the reflection loss(RL)of the CoFe_(2)O_(4)@C composite reaches the maximum value of25.66 dB at 13.92 GHz,and the effective absorbing band(EAB)is 4.59 GHz(11.20-15.79 GHz)when the carbon mass content is 6.01%.The RL and EAB of CoFe_(2)O_(4)@C composite are increased by 219.55%and 4.59 GHz respectively,and the density is decreased by 20.78%compared with the cobalt ferrite.Such enhanced EMW absorption properties of CoFe_(2)O_(4)@C composite are attributed to the attenuation caused by the strong natural resonance of the cobalt ferrite,moreover,the carbon coating layer adjusts the impedance matching of the composite,and the introduced dipole polarization and interface polarization can cause multiple Debye relaxation processes.

From VIB‑to VB‑Group Transition Metal Disulfides:Structure Engineering Modulation for Superior Electromagnetic Wave Absorption

The laminated transition metal disulfides(TMDs),which are well known as typical two-dimensional(2D)semiconductive materials,possess a unique layered structure,leading to their wide-spread applications in various fields,such as catalysis,energy storage,sensing,etc.In recent years,a lot of research work on TMDs based functional materials in the fields of electromagnetic wave absorption(EMA)has been carried out.Therefore,it is of great significance to elaborate the influence of TMDs on EMA in time to speed up the application.In this review,recent advances in the development of electromagnetic wave(EMW)absorbers based on TMDs,ranging from the VIB group to the VB group are summarized.Their compositions,microstructures,electronic properties,and synthesis methods are presented in detail.Particularly,the modulation of structure engineering from the aspects of heterostructures,defects,morphologies and phases are systematically summarized,focusing on optimizing impedance matching and increasing dielectric and magnetic losses in the EMA materials with tunable EMW absorption performance.Milestones as well as the challenges are also identified to guide the design of new TMDs based dielectric EMA materials with high performance.

Hollow Gradient-Structured Iron-Anchored Carbon Nanospheres for Enhanced Electromagnetic Wave Absorption

In the present paper,a microwave absorber with nanoscale gradient structure was proposed for enhancing the electromagnetic absorption performance.The inorganic-organic competitive coating strategy was employed,which can effectively adjust the thermodynamic and kinetic reactions of iron ions during the solvothermal process.As a result,Fe nanoparticles can be gradually decreased from the inner side to the surface across the hollow carbon shell.The results reveal that it offers an outstanding reflection loss value in combination with broadband wave absorption and flexible adjustment ability,which is superior to other relative graded distribution structures and satisfied with the requirements of lightweight equipment.In addition,this work elucidates the intrinsic microwave regulation mechanism of the multiscale hybrid electromagnetic wave absorber.The excellent impedance matching and moderate dielectric parameters are exhibited to be the dominative factors for the promotion of microwave absorption performance of the optimized materials.This strategy to prepare gradient-distributed microwave absorbing materials initiates a new way for designing and fabricating wave absorber with excellent impedance matching property in practical applications.

Rational design of hollow rice-grainedα-Fe_(2)O_(3)/carbon nanofibers with optimized impedance matching for electromagnetic wave absorption enhanced

Electromagnetic wave absorption materials are widely used in electronic equipment and military fields.However,high cost and complex preparation processes become a major obstacle in promoting popularization in the civil field.To solve the problems above,researchers have made great efforts to develop Fe-based carbon composites.However,most of the typical composites require a high filling ratio while achieving excellent properties.Therefore,in this study,carbon nanofibers(CNFs)combined with the hollow rice-grainedα-Fe_(2)O_(3)nanoparticles were prepared by the in-situ transformation method.The rational microstructure design provided a solution for reducing the filling ratio,optimizing impedance matching,and improving electromagnetic wave absorption performance.The strong reflection loss value(−38.1 dB)and broad effective absorption bandwidth(4.6 GHz)for Fe_(2)O_(3)/CNFs composites were achieved with a low filling ratio(20 wt.%),and the analysis of electromagnetic parameters validated that the microstructure of Fe_(2)O_(3)/CNFs plays a crucial role in the performance improvement.With the optimized impedance matching and simple preparation method,Fe_(2)O_(3)/CNFs have broad application prospects in electromagnetic wave absorption.

Facile fabrication of graphene/g-C_(3)N_(4) for electromagnetic wave absorption

With the development of the miniaturization of electronic equipment and lightweight weapon equipment,there are new requirements for electromagnetic wave absorption material(EMWAM).EMWAM has outstanding electromagnetic wave absorption properties and lightweight characteristics become an important direction of research.In this study,graphene/g-C_(3)N_(4)(GGCN)EMWAM was first synthesized in situ by simple heat treatment,in which the g-C_(3)N_(4) had a porous structure and dispersed on the surface of graphene.The impedance matching of the GGCN was well adjusted by decreasing the dielectric constant and attenuation constant due to the g-C_(3)N_(4) semiconductor property and the graphite-like structure.The EMW loss mechanism of GGCN was also analyzed by simulating GGCN’s electric field mode distribution and resistance loss power density.The analysis result shows that the distribution of g-C_(3)N_(4) among GGCN sheets can produce more polarization effects and relaxation effects by increasing the lamellar spacing.Furthermore,the polarization loss of GGCN could be increased successfully by porous g-C_(3)N_(4).Ultimately,the EMW absorption property of GGCN is optimized significantly,and GGCN exhibits excellent EMW absorption performance.When the thickness is 2 mm,the effective absorption bandwidth(EAB)can reach 4.6 GHz,and when the thickness is 4.5 mm,the minimum reflection loss(RLmin)at 4.56 GHz can reach-34.69 dB.Moreover,the practical application of EMWAM was studied by radar cross-section(RCS)simulation,showing that GGCN has a good application prospect.

Research on Electromagnetic Wave Absorption Based on Electrospinning Technology

At present,in order to overcome electromagnetic interference and prevent electromagnetic harm,the research of new and efficient electromagnetic wave absorbing materials has become the research focus in the field of materials science.The one-dimensional structure can promote the impedance matching and attenuation characteristics of the absorbing materials.Electrospinning,as an effective method to prepare nanofibers with high length-diameter ratio,has been widely concerned because it is suitable for struc-tural design of various materials.In this paper,the research progress and absorption properties of nano-fiber materials prepared by electrospinning combined with different processes are introduced.

Flower-like CuS/γ-Fe_(2)O_(3) van der Waals heterostructures with highefficient electromagnetic wave absorption

The escalating electromagnetic(EM)pollution issues and the demand to elevate military stealth technology make it imperative to develop cost-effective and high-performance electromagnetic wave(EMW)absorbing materials.In this paper,the flower-like CuS/γ-Fe_(2)O_(3) van der Waals(vdW)heterostructures have been synthesized via a facile two-step solvothermal approach.The flower-like CuS skeleton increases the attenuation path of EMW while reducing the material density.Different contents ofγ-Fe_(2)O_(3) nanoparticles anchor between the flower-like CuS nanosheets to constitute a heterogeneous structure,which enables dielectric and magnetic loss synergistically to optimize impedance matching and remarkably improve the EMW absorption performance.The minimum reflection loss(RLmin)is-49.36 dB with a thickness of only 1.6 mm and the effective absorption bandwidth(EAB)reaches 4.64 GHz(13.36–18 GHz).By adjusting the thickness of the absorber,the EAB can cover 96%of the GHz band.Notably,the superior absorption of-61.53 dB at middle frequency band can be obtained by adjusting the amount of Fe_(2)O_(3) addition.In this study,the adjustment of EM parameters and the optimization of impedance matching have been achieved by constructing a novel vdW heterogeneous structure,which provides fresh ideas and references for the design of high-performance EMW absorbing materials.

Construction of NiCeO_(x) nanosheets-skeleton cross-linked by carbon nanotubes networks for efficient electromagnetic wave absorption

In this work,two-dimensional NiCeOx nanosheet-modified carbon nanotubes(CNTs)composites were prepared by a hydrothermal method.NiCeOx with different morphologies can be formed by adjusting the addition ratio of nickel salt and cerium salt,and the introduction of CNTs in the subsequent synthesis process can effectively prevent the aggregation of NiCeOx nanosheets.Microstructural studies show that hexagonal NiCeOx nanosheets with a size of 100 nm are uniformly intertwined with CNTs.When applied to the attenuation of electromagnetic waves,NiCeOx/CNTs composites exhibit better electromagnetic wave(EMW)absorption performance than pure CNTs and NiCeOx nanosheets due to improved impedance matching and multiple polarization relaxation.At the matching thickness of 1.9 mm,the composite exhibits a minimum reflection loss(RL_(min))of–53.2 dB and an effective absorption bandwidth(RL<–10 dB)of 5.04 GHz with a thickness of 2.3 mm.These results indicate that the as-prepared NiCeOx/CNTs composites have excellent EMW absorption performance and are expected to be a candidate material for EMW absorption.

Carbon nanotubes decorated FeNi/nitrogen-doped carbon composites for lightweight and broadband electromagnetic wave absorption

Magnetic-dielectric component modulation and heterogeneous interface engineering were considered as an effective strategy for designing lightweight and broadband electromagnetic wave(EMW)absorbors.Herein,a series of carbon nanotubes(CNTs)decorated core-shell nitrogen-doped carbon(CNTs/FeNi/NC)composites were successfully fabricated via the carbonization of CNTs/NiFe_(2)O_(4)/PDA precursors obtained by hydrothermal and polymerization method.The EMW absorption(EMWA)properties of CNTs/FeNi/NC composites were explored by varying the CNTs content.When the CNTs content was 15%,the minimum reflection loss(RL_(min))value was-51.13 dB at 9.52 GHz and the corresponding effective absorption band-width(EAB)value was 2.96 GHz(8.96-11.12 GHz)at 2.5 mm.Particularly,the maximum EAB value can reach up to 4.64 GHz(12.80-17.44 GHz)at 1.7 mm.The excellent EMW attenuation capability resulted from the enhanced conductive loss,polarization loss,magnetic loss,and improved impedance matching.This work offers a novel reference for designing lightweight and broadband EMWA materials.

Boosting electromagnetic wave absorption of Ti_(3)AlC_(2) by improving effective electrical conductivity

Electromagnetic wave-absorbing(EMA)materials at high temperatures are limited by poor conduction loss(L_(c)).However,adding conductors simultaneously increases the conduction loss and interfacial polarization loss,leading to a conflict between impedance matching(Z_(in)/Z_(0))and electromagnetic wave loss.This will prevent electromagnetic waves from entering the EMA materials,finally reducing overall absorbing performance.Here,the effective electrical conductivity(σ)is enhanced by synchronizing particle size and grain number of Ti_(3)AlC_(2) to increase the conduction loss and avoid the conflict between the impedance matching and the electromagnetic wave loss.As a result,the best-absorbing performance with an effective absorption bandwidth(EAB)of 4.8 GHz(10.6–15.4 GHz)at a thickness of only 1.5 mm is realized,which is the best combination of wide absorption bandwidth and small thickness,and the minimum reflection loss(RL_(min))reaches−45.6 dB at 4.1 GHz.In short,this work explores the regulating mechanism of the EMA materials of effective electrical conductivity by simulated calculations using the Vienna ab-initio Simulation Package(VASP)and COMSOL as well as a series of experiments,which provide new insight into a rational design of materials with anisotropic electrical conductivity.

Achieving ultra-broadband electromagnetic absorption of Ag regulated hollow Ag/CuO@CuS through balancing conduction loss and impedance matching

Excellent impedance matching and high conduction loss are important factors for the preparation of high-performance electromagnetic wave(EMW)absorbing materials,but these two properties are of-ten contradictory.In this work,three absorbers with unique hollow structures,H-Ag/CuO@CuS,H-O-Ag/CuO@CuS,and H-P-Ag/CuO@CuS,are designed and synthesized by adopting hollow CuO@CuS with double shell as carrier and silver nitrate as the structural regulator.The more voids coming from hol-low structures,window-opened structures,and stacked pores improve the impedance matching of these absorbers,and the introduction of elemental Ag effectively regulates the conduction loss.Therefore,a balance between impedance matching and conduction loss is achieved to improve the reflection loss(RL)value and broadens the absorbing band of the absorbers.In comparison to H-Ag/CuO@CuS and H-O-Ag/CuO@CuS(hollow structure with open window)in which elemental Ag is uniformly dispersed in the CuO layer,H-P-Ag/CuO@CuS exhibits more excellent EMW absorption performance due to more voids and an optimized conductive network arising from Ag/CuO pieces distributed between the hol-low Ag/CuO@CuS particles and Ag distributed in the CuS layer.When the thickness is 2.3 mm,H-P-Ag/CuO@CuS provides an ultra-wide electromagnetic absorption band of 8.56 GHz(9.44-18 GHz),in which the RL<-10 dB and the minimum reflection loss of-41 dB.

Lightweight,self-cleaning and refractory FeCo@MoS_(2)PVA aerogels:from electromagnetic wave-assisted synthesis to flexible electromagnetic wave absorption

The emergence of wearable and foldable electronic devices urges advanced electromagnetic(EM)wave absorbers with maintained performance under deformation.Here FeCo@MoS_(2)poly vinyl alcohol(PVA)aerogels have been fabricated with the assistance of EM waves for simultaneous splitting of the MoS_(2)flakes and dispersive growth of FeCo nanoparticles.The resultants in-return have been used for EM wave absorption with excellent performance,providing minimum reflection loss(RL_(min))of-40.7 dB and a broad effective absorption bandwidth(EAB)of 6.4 GHz at a thickness of 2.5 mm.Real-time compression has been introduced to reveal the evolution of EM parameters.The aerogels maintain satisfactory performance even under 50%compression due to the balance of impedance matching and attenuation.Despite the deterioration of impedance matching,the attenuation is significantly enhanced due to both strengthened conductive loss and magnetic loss.In addition,features such as lightweight,self-cleaning and refractory can be achieved for the aerogels for applications in complex environments.As such this work not only provides a versatile synthetic route assisted by EM wave energy,but also insights on the evolution of absorption performance under deformation together with the design strategy of multifunctional flexible wave absorbers.

Bifunctional SiC/Si_(3)N_(4) aerogel for highly efficient electromagnetic wave absorption and thermal insulation

SiC ceramics are attractive electromagnetic(EM)absorption materials for the application in harsh environment because of their low density,good dielectric tunable performance,and chemical stability.However,the performance of current SiC-based materials to absorb EM wave is generally unsatisfactory due to poor impedance matching.Herein,we report ultralight SiC/Si3N4 composite aerogels(~15 mg·cm^(−3))consisting of numerous interweaving SiC nanowires and Si3N4 nanoribbons.Aerogels were prepared via siloxane pyrolysis and chemical vapor reaction through the template method.The optimal aerogel exhibits excellent EM wave absorption properties with a strong reflection loss(RL,−48.6 dB)and a wide effective absorption band(EAB,7.4 GHz)at a thickness of 2 mm,attributed to good impedance matching and multi attenuation mechanisms of waves within the unique network structure.In addition,the aerogel exhibits high thermal stability in air until 1000℃and excellent thermal insulation performance(0.030 W·m^(−1)·K^(−1)).These superior performances make the SiC/Si_(3)N_(4) composite aerogel promising to become a new generation of absorption material served under extreme conditions.

Interface Engineering of Titanium Nitride Nanotube Composites for Excellent Microwave Absorption at Elevated Temperature

Currently,the microwave absorbers usually suffer dreadful electromagnetic wave absorption(EMWA)performance damping at elevated temperature due to impedance mismatching induced by increased conduction loss.Consequently,the development of high-performance EMWA materials with good impedance matching and strong loss ability in wide temperature spectrum has emerged as a top priority.Herein,due to the high melting point,good electrical conductivity,excellent environmental stability,EM coupling effect,and abundant interfaces of titanium nitride(TiN)nanotubes,they were designed based on the controlling kinetic diffusion procedure and Ostwald ripening process.Benefiting from boosted heterogeneous interfaces between TiN nanotubes and polydimethylsiloxane(PDMS),enhanced polarization loss relaxations were created,which could not only improve the depletion efficiency of EMWA,but also contribute to the optimized impedance matching at elevated temperature.Therefore,the TiN nanotubes/PDMS composite showed excellent EMWA performances at varied temperature(298-573 K),while achieved an effective absorption bandwidth(EAB)value of 3.23 GHz and a minimum reflection loss(RLmin)value of−44.15 dB at 423 K.This study not only clarifies the relationship between dielectric loss capacity(conduction loss and polarization loss)and temperature,but also breaks new ground for EM absorbers in wide temperature spectrum based on interface engineering.

Recent advance in three-dimensional porous carbon materials for electromagnetic wave absorption

With the increasingly serious electromagnetic wave(EMW)pollution,the development of high-performance EMW absorbing materials(EWAMs)has become a hot topic.Carbon-based EWAMs have excellent chemical stability,high electrical conductivity,and strong dielectric loss.In particular,three-dimensional(3D)porous carbon-based EWAMs have been widely developed in the EMW absorption field.The 3D porous structure not only reduces the materials’mass density,but also improves the multiple reflections of incident EMWs and impedance matching.The carbon-based EWAMs are thus expected to achieve the goals of low density,low thickness,wide absorption bandwidth,and strong absorption.Herein,we first restated the relevant theoretical basis and evaluation methods.Then,we summarized the recent research progress of 3D porous carbon-based EWAMs with the source of the materials as the main clue.Some unique and novel viewpoints were highlighted.Finally,the challenges and prospects of 3D porous carbon-based EWAMs were put forward,which is helpful for guiding a further development of high-performance EWAMs.

N-doped residual carbon from coal gasification fine slag decorated with Fe_(3)O_(4)nanoparticles for electromagnetic wave absorption

The electromagnetic wave absorption(EMWA)performance of materials is affected by their dielectric and magnetic properties.Here,ferroferric oxide@N-doped residual carbon(Fe_(3)O_(4)@NRC)composites were successfully fabricated by decorating NRC with Fe_(3)O_(4)nanoparticles via a facile chemical co-precipitation method.The RC was obtained through acid treatment to remove the inorganic minerals in coal gasification fine slag.The structure,composition,thermal stability,morphology,and related EM parameters of the as-fabricated Fe_(3)O_(4)@NRC composites were thoroughly tested via analytical techniques.Notably,both the Fe_(3)O_(4)@NRC-2 and Fe_(3)O_(4)@NRC-3 composites exhibited superior EMWA capacity.When 40%mass was added,the value of minimal reflection loss(RL_(min))for Fe_(3)O_(4)@NRC-2 was-37.4 dB,and the effective absorption bandwidth(EAB,RL≤-10 dB)reached 4.16 GHz(13.84-18.00 GHz)at a thickness of 1.5 mm.Besides,the value of impedance matching was 1.00 as the RL_(min)was achieved.The results demonstrated that the EMWA performance of the composites could be adjusted by controlling the content of Fe_(3)O_(4)nanoparticles.The magnetic/carbon composites exhibited superior EMWA performance,thus promoting the resource utilization of residual carbon in coal gasification fine slag from coal gasification.

Novel magnetic silicate composite for lightweight and efficient electromagnetic wave absorption

A series of silicates with double shell hollow sphere morphology were prepared by hydrothermal method with ultra-high temperature calcined,and used in the field of electromagnetic(EM)wave absorption.By characterizing the chemical composition,crystal structure,micro morphology and EM parameters of the several materials,the evaluation results of EM wave absorption capacity of the materials were obtained.In the discussion section,we will discuss the reasons for the differences in EM wave absorption capabilities of the several silicates from multiple aspects such as EM wave absorption mechanism in detail.Especially for iron-based silicate(HGMs@Fe_(2)SiO_(4))materials,after reasonable composition and morphology design,the minimum reflection loss(RLmin)reached up to-41.14 d B with a matching thickness(d)of 3.4 mm,and the corresponding effective absorption bandwidth(f_(E),RL<-10 d B)was 6.80 GHz.Because of the wide EM wave absorption bandwidth,light weight and low water absorption,this kind of double shell silicate material has gained huge application potential in the EM wave absorption field.

Lightweight PPy aerogel adopted with Co and SiO_(2) nanoparticles for enhanced electromagnetic wave absorption

Lightweight nanocomposites consisting of magnetic and dielectric units aroused intensive interest as potential high performance electromagnetic wave absorbing materials.In this work,we report a facile and efficient method to fabricate(Co,SiO_(2))/PPy composites with tunable electromagnetic properties.The absorbing properties and effective absorbing bandwidth can be regulated by controlling the content of SiO_(2) in composites.The composite shows a maximum reflection loss(RL)of-65.31 d B at 11.12 GHz with a thickness of 3.002 mm when SiO_(2) being 22 wt.%.The effective absorbing bandwidth reaches up to 5.1 GHz(8.91-14.01 GHz),which covers the entire X band(8-12 GHz).The improved impedance matching,high interfacial polarization and complex electromagnetic synergy in the composites are the key factors giving rise to the higher efficient absorption.The PPy aerogel-based nanocomposites with controllable absorption performance,lower density and strong environmental adaptability will become attractive candidates as advanced microwave absorbing materials.

Mixed-dimensional hierarchical configuration of 2D Ni_(2)P nanosheets anchored on 1D silk-derived carbon fiber for extraordinary electromagnetic wave absorption

Considering a series of electromagnetic pollution problems brought by the development of electronic communication technology,more attention has been paid to the research of electromagnetic wave(EMW)absorbing materials with unique composition and structure.Herein,under the inspiration of mixeddimensional hierarchical structure,2D Ni_(2)P nanosheets anchored on 1D silk-derived carbon fiber is successfully fabricated as a gratifying resistor-dielectric type absorber.By a controllable pyrolyzation strategy and disproportionated reaction,high-density 2D Ni_(2)P nanosheets were grown vertically and cross-linked on the surface of 1D silk-derived carbon fiber.The sample exhibited superior EMW absorption performance with maximum reflection loss value of–56.9 d B at the thickness of 2.32 mm and the effective absorption bandwidth can reach to 7.2 GHz at the thickness of 1.93 mm.In addition,the pure Ni_(2)P shows remarkable dielectric characteristic and EMW absorption ability as well.The integration of dualconductive loss,enhanced polarization relaxation loss and the multiple scattering in the composites was proved to contribute to the good EMW absorption performance.Therefore,this work confirms the great potentials of Ni_(2)P as a high-efficient EMW absorbing materials and light a new way in construction of multidimensional absorber.

Preparation and Microwave Absorbing Properties of Double-layer Fine Iron Tailings Cementitious Materials

To develop the microwave absorbing(MA)properties of cementitious material mixed with mine solid waste,the iron tailings cementitious microwave absorbing materials were prepared.The iron tailings was treated into different particle sizes by planetary ball mill,and the physicochemical properties of iron tailings were tested by laser particle size analyzer and scanning electron microscope(SEM).The electromagnetic parameters of iron tailings cementitious materials were characterized by a vector network analyzer and simulated MA properties,and the MA properties of iron tailings-cement composite system with steel fiber as absorber was studied.Based on the design of the single-layer structure,optimum mix ratio and thickness configuration method of double-layer structure were further studied,meanwhile,the mechanical properties and engineering application were analyzed and discussed.The results show that the particle size of iron tailings can afiect its electromagnetic behavior in cementitious materials,and the smaller particles lead the increase of demagnetisation efiect induced by domain wall motion and achieve better microwave absorbing properties in cementitious materials.When the thickness of matching layer and absorbing layer is 5 mm,the optimized microwave absorbing properties of C1/C3 double-layer cementitious material can obtain optimal RL value of-27.61 dB and efiective absorbing bandwidth of 0.97 GHz,which attributes to the synergistic efiect of impedance matching and attenuation characteristics.The double-layer microwave absorbing materials obtain excellent absorbing properties and show great design flexibility and diversity,which can be used as a suitable candidate for the preparation of favorable microwave absorbing cementitious materials.