Exploring lightweight microwave attenuation materials with strong and tunable wideband microwave absorption is highly desirable but remains a significant challenge. Herein, three-dimensional （3D） porous hybrid compo...Exploring lightweight microwave attenuation materials with strong and tunable wideband microwave absorption is highly desirable but remains a significant challenge. Herein, three-dimensional （3D） porous hybrid composites consisting of NiFe nanoparticles embedded within carbon nanocubes decorated on graphene oxide （GO） sheets （NiFe@C nanocubes@GO） as high-performance microwave attenuation materials have been rationally synthesized. The 3D porous hybrid composites are fabricated by a simple method, which involves one-step pyrolysis of NiFe Prussian blue analogue nanocubes in the presence of GO sheets. Benefiting from the unique structural features that exhibit good magnetic and dielectric losses as well as a proper impedance match, the resulting NiFe@C nanocubes@GO composites show excellent microwave attenuation ability. With a minimum reflection loss （RL） of -51 dB at 7.7 GHz at a thickness of 2.8 mm and maximum percentage bandwidth of 38.6% for RL 〈 -10 dB at a thickness of 2.2 mm, the NiFe@C nanocubes@GO composites are superior to the previously reported state-of-the-art carbon-based microwave attenuation materials.展开更多
To achieve excellent electromagnetic wave(EMW)absorption properties,the microstructure design of the absorber is critical.In this work,six kinds of N-Ni/C nanostructures with different morphologies were prepared by on...To achieve excellent electromagnetic wave(EMW)absorption properties,the microstructure design of the absorber is critical.In this work,six kinds of N-Ni/C nanostructures with different morphologies were prepared by one-step hydrothermal method and high temperature carbonization by adjusting the types of nickel salts and reaction solvents.The EMW absorption performance of six different morphologies of N-Ni/C nanostructures was compared and analyzed.Among them,it is found that the nanoflowerlike N-Ni/C composite has excellent dielectric loss and magnetic loss synergistic effect due to its polycrystalline structure,and can obtain excellent EMW absorption performance.The minimum reflection loss value at a thickness of 1.9 mm is-59.56 dB at 16.88 GHz,and the effective absorption bandwidth value reaches 6.0 GHz at a thickness of 2.2 mm.Our research shows that different morphologies and multiple lattice structures of nanostructures with the same composition have a significant influence on EMW absorption performance,which provides new research ideas for developing high-performance EMW absorbing materials.展开更多
Impedance matching characteristics and loss capabilities including magnetic loss,polarization loss and conduction loss are critical factors to improve microwave absorption performances(MAPs).To elevate these aspects,h...Impedance matching characteristics and loss capabilities including magnetic loss,polarization loss and conduction loss are critical factors to improve microwave absorption performances(MAPs).To elevate these aspects,herein,yolk-shell structured CoNi@Air@C/SiO_(2)@Polypyrrole(PPy)magnetic multicomponent nanocubes(MCNCs)were designed and successfully fabricated in high efficiency through a continuous co-precipitation route,classical Stöber method,thermal treatment and polymerization reaction.The obtained results indicated that the formation of SiO_(2) effectively stabilized the cubic geometrical morphology and yolk-shell structure during the high-temperature pyrolysis process.The introduction of PPy greatly boosted their polarization loss and conductive loss capabilities.Therefore,the as-prepared yolkshell structured CoNi@Air@C/SiO_(2)@PPy MCNCs presented superior MAPs compared to CoNi@Air@C/SiO_(2) MCNCs.Furthermore,by regulating the content of PPy,the obtained CoNi@Air@C/SiO_(2)@PPy MCNCs displayed tunable and excellent comprehensive MAPs in terms of strong absorption capabilities,broad frequency bandwidths and thin matching thicknesses,which could be ascribed to the unique structure and excellent magnetic-dielectric synergistic effect.Therefore,our findings provided an alternative pathway to effectively utilize the magnetic-dielectric synergy and loss capabilities for the developing yolk-shell structured magnetic MCNCs as the strong wideband microwave absorbers.展开更多
The dielectric and electromagnetic properties of two types of SiC fibres with different compositions were investigated. The permittivity and electromagnetic shielding effectiveness （SE） of SiC fibre bundles were mea...The dielectric and electromagnetic properties of two types of SiC fibres with different compositions were investigated. The permittivity and electromagnetic shielding effectiveness （SE） of SiC fibre bundles were measured in 8.2-12.4 GHz by waveguide method. The reflection coefficient （RC） of unidirectional SiC fibre laminates was determined in 8-18 GHz using naval research laboratory （NRL）-arc method. Results showed that the electromagnetic wave （EMW） absorbing properties of SiC fibres were correlated with their composition, microstructure and instinct performance of electrical resistance. SiC fibres with higher content and greater size of nano-scale H-SiC showed higher permittivity, conductivity, SE and lower RC, which resulted in their better EMW absorbing ability, Le. the lower reflection to EMW.展开更多
Growing electromagnetic pollution has plagued researchers in the field of electromagnetic(EM)energy dissipation for many years;it is increasingly important to solve this problem efficiently.Metal-organic frameworks(MO...Growing electromagnetic pollution has plagued researchers in the field of electromagnetic(EM)energy dissipation for many years;it is increasingly important to solve this problem efficiently.Metal-organic frameworks(MOFs),a shining star of functional materials,have attracted great attention for their advantages,which include highly tunable porosity,structure,and versatility.MOF-derived electromagnetic wave(EMW)absorbers,with advantages such as light weight,thin matching thickness,strong capacity,and wide effective bandwidth,are widely reported.However,current studies lack a systematic summary of the ternary synergistic effects of the precursor component-structure-EMW absorption behavior of MOF derivatives.Here we describe in detail the electromagnetic(EM)energy dissipation mechanism and strategy for preparing MOF-derived EMW absorbers.On the basis of this description,the following means are suggested for adjusting the EM parameters of MOF derivatives,achieving excellent EM energy dissipation:(1)changing the metal and ligands to regulate the chemical composition and morphology of the precursor,(2)controlling pyrolysis parameters(including temperature,heating rate,and gas atmosphere)to manipulate the structure and components of derivatives,and(3)compounding with enhancement phases,including carbon nanomaterials,metals,or other MOFs.展开更多
The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal–organic frameworks(MOFs)and graphene oxide(GO)building blocks that exhibit an ultralow density and unif...The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal–organic frameworks(MOFs)and graphene oxide(GO)building blocks that exhibit an ultralow density and uniformly distributed MOFs on GO sheets is important for various applications.Herein,we report a facile route for synthesizing MOF/reduced GO(rGO)aerogels based on the gelation of GO,which is directly initiated using MOF crystals.Free metal ions exposed on the surface of MIL-88A nanorods act as linkers that bind GO nanosheets to a three-dimensional porous network via metal–oxygen covalent or electrostatic interactions.The MOF/rGOderived magnetic and dielectric aerogels Fe_(3)O_(4)@C/rGO and Ni-doped Fe_(3)O_(4)@C/rGO show notable microwave absorption(MA)performance,simultaneously achieving strong absorption and broad bandwidth at low thickness of 2.5(-58.1 dB and 6.48 GHz)and 2.8 mm(-46.2 dB and 7.92 GHz)with ultralow filling contents of 0.7 and 0.6 wt%,respectively.The microwave attenuation ability of the prepared aerogels is further confirmed via a radar cross-sectional simulation,which is attributed to the synergistic effects of their hierarchically porous structures and heterointerface engineering.This work provides an effective pathway for fabricating hierarchically porous MOF/rGO hybrid aerogels and offers magnetic and dielectric aerogels for ultralight MA.展开更多
3D reticulated ceramics (3DRCs) with the composition containing SrFe12O19-SiC-TiO2 were prepared by a replication process with polyurethane sponges as the template in ceramic slurry. The electrical conductivity, diele...3D reticulated ceramics (3DRCs) with the composition containing SrFe12O19-SiC-TiO2 were prepared by a replication process with polyurethane sponges as the template in ceramic slurry. The electrical conductivity, dielectric and magnetic parameters of 3D reticulated ceramics (3DRCs) were measured with changes in cell size of the sponges, contents in the slurry and sintering temperature in this paper. Discussions about the influential factors of those parameters were focused on their electrical conductivity. The experimental results indicated that the electrical conductivity of 3DRCs raised with the increase of cell size, SiC/SrO 6Fe2O3 with weight ratio and sintering temperature. X-ray diffractions and SEM were used to investigate the relationship between electrical conductivity and sintering temperature. Deoxidizing reactions of SrO 6Fe2O3 caused the increasing electrical conductivity. The real part of permittivity (ε') and imaginary part of permeability (μ') raised with the increase of electrical conductivity (σ). The imaginary part of permittivity (ε') has a maximum at 10o S/cm with the increase of a, and the real part of permeability (μ') changes slightly with the increase of a. When a is at the range of 10-4 S/cm to 10o S/cm (a semi conductive state), both the imagine part of permittivity and permeability raises with increasing a, therefore, the 3DRCs present their high electromagnetic loss properties.展开更多
Microwave absorbing properties of the carbonyl iron particles filled epoxy-silicone resin coatings showed visible degression when the coatings were heat treated at 300 ℃ with different time.The complex permittivity a...Microwave absorbing properties of the carbonyl iron particles filled epoxy-silicone resin coatings showed visible degression when the coatings were heat treated at 300 ℃ with different time.The complex permittivity and permeability of the coatings before and after heat treatment were measured.After heat treatment at 300 ℃,the real part of permittivity of the coatings increased with increasing treatment time and showed frequency dependence dielectric response.The complex permeability showed remarkable variation while the resonance frequency of the coatings heat treated at 300 ℃ shifted from 7 to 12 GHz.The electromagnetic results indicated that microwave absorbing properties of the coatings showed more dependent on the complex permeability.The results showed that the difference of the electromagnetic and microwave absorbing properties before and after heat treatment was mainly attributed to the crystalline state transition of carbonyl iron particles.展开更多
Materials that can absorb electromagnetic(EM)wave have garnered increased attention in recent years due to their potential to mitigate the ever increasing environmental pollution by EM waves.Thanks to recent advances ...Materials that can absorb electromagnetic(EM)wave have garnered increased attention in recent years due to their potential to mitigate the ever increasing environmental pollution by EM waves.Thanks to recent advances in micro/nanofabrication,a variety of magnetic metal-based EM absorbers have been reported.The design and synthesis of EM absorbers that exhibit efficient and wide-band absorption at small thicknesses,however,remains elusive.Here we report the design of fibrous nanostructures consisting of magnetic iron(Fe)nanoparticles and carbon nanotubes(CNTs),which exhibits a wide-band EM absorption(3.8 GHz)while maintain the thickness at 1.2 mm.In our work,we created a novel core-shell structure by immersing the highly fibrous CNT-Fe structure into solid-state silicon(SiO)matrix.Finally,the SiO-coated CNT-Fe structures exhibit good stability against air-induced oxidation and acid corrosion while maintaining high EM absorption.Overall,the results reported in this study present new avenues to absorb EM from ambient air.We believe that our work elevates the utility of EM absorbers to real-world applications such as anti-acid and oxidation ability.展开更多
Copper and rare earth-doped(RE = La, Gd, Nd) CuFe1.85RE0.15O4nano ferrites were prepared using the so nochemical method. The effective doping of rare-earth(La3+, Nd3+, Gd3+) ions with copper nanoferrites was confirmed...Copper and rare earth-doped(RE = La, Gd, Nd) CuFe1.85RE0.15O4nano ferrites were prepared using the so nochemical method. The effective doping of rare-earth(La3+, Nd3+, Gd3+) ions with copper nanoferrites was confirmed by X-ray diffraction. The tetrahedral and octahedral sites of the nano ferrites were identified through the Fourier transform infrared spectra. The doping of rare-earth elements enhances the optical bandgap energy of the nanoferrites that are observed through Ultraviolet-DRS spectra. The oxidation state of the elements Cu 2 p, La 3 d, Nd 3 d, Gd 3 d, Fe 2 p and O 1 s was analyzed. Scanning electron microscopy images indicate a spherical morphology with agglomeration to some elongate. The values of dielectric constant and conductivity decrease considerably due to doping rare-earth ions in copper nanoferrites. Low saturation magnetization and high coercivity values of rare earth-doped copper nanoferrites are observed from the typical hysteresis curves.展开更多
Metamaterials are widely used in electromagnetic radiation and camouflage for their flexible wavefront manipulation and polarization over a broad spectrum ranging from microwaves to optics.However,multispectral compat...Metamaterials are widely used in electromagnetic radiation and camouflage for their flexible wavefront manipulation and polarization over a broad spectrum ranging from microwaves to optics.However,multispectral compatible camouflage faces significant challenges due to tremendous scale differences of unit cells and desired radiative properties in various spectral regimes.This study assembles a micron-scale infrared emitter,a millimeter-scale microwave absorber,and a metal reflector to propose a hierarchical metamaterial that reduces microwave scattering and reflects low-infrared waves.As a proof of concept,laser etching micro-manufactures an upper infrared shielding layer with a periodic metal pattern.At the same time,bottom square frustum metastructure composites are fabricated and optimized based on genetic algorithms.Under the normal incidence transverse electromagnetic wave with a 90°azimuth angle,the hierarchical strategy and infrared unit create an asymmetric electric field distribution of local near-field coupling,which is conducive to generating additional resonance for broadening the absorption bandwidth.Experiments verify the multispectral camouflage,which shows a high absorption efficiency of more than 90%,ranging from 3.6 to 6.2 and from 8.4 to 18 GHz with a total thickness of 4.05 mm(0.049λmax).Due to the non-reflection of surrounding thermal signals in the infrared 2-22μm region,low-infrared emissivity(0.29)metamaterials can adapt to various thermal backgrounds.This methodology can provide a novel route for fabricating multispectral camouflage devices.展开更多
Saturation magnetization,magneto-crystalline anisotropy field,and dielectric properties are closely related to microwave devices applied at different frequencies.For regulating the magnetic and dielectric properties o...Saturation magnetization,magneto-crystalline anisotropy field,and dielectric properties are closely related to microwave devices applied at different frequencies.For regulating the magnetic and dielectric properties of W-type barium ferrites,single-phase BaMe_(2)Fe_(16)O_(27)(Me=Fe,Mn,Zn,Ni,Co) with different Me ions were synthesized by the high-temperature solid-state method.The saturation magnetization(Ms) range from 47.77 emu/g to 95.34 emu/g and the magnetic anisotropy field(H_a) range from 10700.60 Oe(1 Oe=79.5775 A·m^(-1)) to 13739.57 Oe,depending on the type of cation substitution in the hexagonal lattice.The dielectric permittivity and dielectric loss decrease with increasing frequency of the AC electric field in the low-frequency region,while they almost remain constant in the high-frequency region.The charac teristics of easy regulation and preparation make it a potential candidate for use in microwave device applications.展开更多
In this work,the magnetic,dielectric properties and electric modulus of Ce^(3+) substituted cobaltmagnesium(Co_(0.7)Mg_(0.3)Ce_(x)Fe_(2-x)O_4)(labeled as CMCF) ferrite nanoparticles were investigated in detail.Saturat...In this work,the magnetic,dielectric properties and electric modulus of Ce^(3+) substituted cobaltmagnesium(Co_(0.7)Mg_(0.3)Ce_(x)Fe_(2-x)O_4)(labeled as CMCF) ferrite nanoparticles were investigated in detail.Saturation magnetization decreases from 50.05 to 34.87 emu/g for further substituting Ce^(3+) ions.Meanwhile,coercivity increases from 738.22 Gs for the CMCFO sample to 912.10 Gs for the CMCF2 sample,then decreases monotonically to 762.1 Gs for the CMCF5 sample.The cerium content and particle size play important roles in controlling the magnetization and coercivity of the CMCF nanoparticles.All CMCF nanoferrites are suitable for microwave applications since their high-frequency response ranges from 7.72 to 11.07 GHz.The CMCF nanoferrites' dielectric parameter dispersion exhibits normal behavior.The pristine Co-Mg nanoferrite only has ε' value of 28.25,but the nanoferrite MCMF2 has ε' value of365.03,with an enhancing ratio of 1192%.The conduction mechanism of the MCMF nanoferrites was determined by fitting the σ_(ac) results via the Jonscher power law.At 653 K,large polaron tunnelling is thought to be responsible for this conduction process,which is followed by electron barrier hopping at higher temperatures.Cole-Cole diagrams at different temperatures,assuring the contributions of the grains and their boundaries at lower temperatures(653 K) and only the grains at higher temperatures.Based on our results,the CMCF nanoferrites hold magnetic and semiconducting nature,which can be used in magnetic devices and dielectrics in lower-frequencies or conductors in higher-frequencies.展开更多
The combination of high efficiency and environmental stability is vital to promote the commercial appli-cations of microwave absorption(MA)materials,yet remains challenging in the absence of facile routes.Here,we put ...The combination of high efficiency and environmental stability is vital to promote the commercial appli-cations of microwave absorption(MA)materials,yet remains challenging in the absence of facile routes.Here,we put forward a graphene-reinforced construct approach for one-pot synthesis of 3D intercon-nected magnetic-dielectric frameworks via pre-functionalization and subsequent assembly.Multiple in-teractions among discrete precursors are capable of manipulating the confined growth and interfacial self-assembly.Significant enhancements in MA properties are triggered in a straightforward manner us-ing ultralow feeding fractions of graphene oxide nanosheet.The minimum reflection loss is up to-60.1 dB(99.9999%wave absorption)and the effective absorption bandwidth reaches 5.9 GHz(almost covering the Ku band).Remarkably,based on the optimization by ultralow concentrations of graphene,the as-prepared nanoarchitecture simultaneously integrates strong absorption,broad bandwidth,and low matching thick-ness.The embedded graphene nanosheets serve as high-speed electron transmission channels and hollow resonance cavities,facilitating multimode attenuations and impedance-matching characteristics.Mean-while,the graphene-reinforced framework suppresses the corrosion of magnetic components,whose cor-rosion rate reduces by an order of magnitude.This study provides a simple procedure to boost magnetic-dielectric absorbers for comprehensive MA performances and enhanced corrosion resistance.展开更多
Aerogel-based composites hold promising application prospects as potential electromagnetic wave(EMW)absorption materials,yet the construction of such materials with ingenious microstructures,appropriate magnetic/diele...Aerogel-based composites hold promising application prospects as potential electromagnetic wave(EMW)absorption materials,yet the construction of such materials with ingenious microstructures,appropriate magnetic/dielectric multi-components,and integrated multifunctionality remains considerably challenging.Herein,a multicomponent Co/MnO/Ti_(3)C_(2)Tx MXene/rGO(CMMG)hybrid aerogel featured with three-dimensional(3D)vertical directional channel architecture is reported.Benefiting from the synergistic effect arising from the 3D conductive networking structure,diverse heterogeneous interfaces,magnetic/dielectric multicomponent,and multiple loss pathways,the optimized CMMG-2 aerogel delivers fascinating EMW absorption capabilities,characterized by a minimal reflection loss(RL_(min))of-77.41 dB and an effective absorption bandwidth(EAB)of 6.56 GHz.Additionally,the remarkable hydrophobicity,exceptional thermal insulation capabilities,and outstanding photothermal properties of CMMG-2 aerogel make it highly promising for multiple application in diverse and demanding environments.Interestingly,the distinctive pore structure of hybrid aerogel also allows it for sensitive and reliable detection of electrical signals caused by pressure changes and human motion.Thus,this research provides a viable design strategy for the development of lightweight,efficient,and multifunctional aerogel-based EMW absorption materials for various application scenarios.展开更多
The spinel cobalt chromium zinc ferrites（Co0.7Cr0.1Zn0.2Fe2O4） and the polyaniline（PANI）-Co0.7Cr0.1Zn0.2Fe2O4 composites were prepared by polyacrylamide gel and an in situ polymerization method,respectively.The st...The spinel cobalt chromium zinc ferrites（Co0.7Cr0.1Zn0.2Fe2O4） and the polyaniline（PANI）-Co0.7Cr0.1Zn0.2Fe2O4 composites were prepared by polyacrylamide gel and an in situ polymerization method,respectively.The structure of the synthesized material was characterized by X-ray diffraction（XRD） and Fourier transform infrared spectrometer（FTIR）,which shows that the spinel Co0.7Cr0.1Zn0.2Fe2O4 ferrites and the PANI Co0.7Cr0.1Zn0.2Fe2O4 composites are obtained.As a small amount of Co^2＋ in the octahedron ferrite is replaced by Cr^3＋,the lattice constant of Co0.8Cr0.2Zn0.2Fe2O4 ferrites reduces from0.8409 to 0.8377 nm.The magnetic properties of the two materials were investigated by vibrating sample magnetometer（VSM）.The VSM results confirm that the saturation magnetization（Ms）,remanent magnetization（Mr） and coercive force（Hc） of the PANI-Co0.7Cr0.1Zn0.2Fe2O4composites are 8.80 mA·m^2·g^-1,3.14 mA·m^2·g^-1 and37.22 kA·m^-1,respectively,which are smaller than those of the Co0.7Cr0.1Zn0.2Fe2O4 ferrites.The microwave absorbing capability of the two materials was studied by waveguide method.In the frequency range of 5-20 GHz,two reflection loss maximum values of the PANI-Co0.7Cr0.1Zn0.2Fe2O4 composites appear at 14.1 and 17.9 GHz with-13.17 and-15.36 dB,respectively,which are obviously higher than those of the Co0.7Cr0.1Zn0.2Fe2O4 ferrites.展开更多
The scattered field and differential scattered section （DSS） of a moving spherical particle with a high speed are investigated numerically. The coordinate and vector transformations are used to establish a theoretic...The scattered field and differential scattered section （DSS） of a moving spherical particle with a high speed are investigated numerically. The coordinate and vector transformations are used to establish a theoretical basis for studying the laser scattering of a moving particle. The DSS of a moving spherical particle is explained by the electric and magnetic field from Mie scattering theory. Assuming the laser wavelength of 1.06μ m, we compute the ratio of the laser DSS of the moving dielectric spherical particle to that of the static dielectric spherical particle, which changes with radii, speeds and scattering angles of the particle. The numerical results show that the laser DSS of the moving spherical particle is tightly connected with its speed and scattering zenith angle. If a spherical particle moves with high speed, the laser DSS due to movement of the particle could not be neglected. If the speed of the dielectric spherical particle is fluctuating, the Doppler effect and the frequency spectrum expansion play important roles.展开更多
In the present study,rare earth samarium(Sm^(3+))substituted Ni-Cu spinel ferrites with the composition of Ni_(0.1)Cu_(0.9)Sm_(x)Fe_(2-x)O_(4)(0≤x≤0.05 in steps of 0.01)were synthesized by using the citrate induced ...In the present study,rare earth samarium(Sm^(3+))substituted Ni-Cu spinel ferrites with the composition of Ni_(0.1)Cu_(0.9)Sm_(x)Fe_(2-x)O_(4)(0≤x≤0.05 in steps of 0.01)were synthesized by using the citrate induced sol-gel auto combustion technique.These ferrites'structural,optical,magnetic,and dielectric studies were carried out using X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),field emission scanning electron microscopy(FESEM),ultraviolet-visible(UV-vis),a vibrational sample magnetometer(VSM),and an LCR meter.The pure Ni-Cu ferrite exhibits a tetragonal structure owing to the presence of the John Tellar ion(Cu^(2+)).XRD patterns confirm that the tetragonal structure gradually transforms into the cubic spinel structure with samarium substitution.The nano-scale structures of these ferrites were confirmed by the average crystallite size(10.11-20.99 nm)derived from the X-ray diffraction patterns,and grain size(42.60-83.36 nm)assessed from FESEM photographs.The existence of elements according to their chemical composition was verified by using energy dispersive X-ray(EDX)spectra.The absorption bands(v_(1) and v_(2))detected in FTIR transmission spectra below the wavenumber of 600 cm^(-1)reveal the stretching vibrations of M-O bonds in the spinel structure at tetrahedral and octahedral locations.The band gap ene rgy obtained from UV absorption reveals the semiconducting nature of the samples.The high saturation magnetization(M_(s))is noticed at 15 K temperature for x=0.02 composition as 32.98 emu/g,while at 300 K for x=0.01composition as 27.61 emu/g.The suggested cation distribution is in good agreement with observed and predicted magnetic moment values at 300 K.The expected behavior of ferrites reveals the observed dielectric constant,loss tangent,and ac-conductivity values in the frequency range of 20 Hz-20 MHz.Cole-Cole plots confirm that the impedance contribution is attributed to grain boundaries.展开更多
Most reported electromagnetic wave absorption(EWA)materials show significant effective absorption in a certain frequency range,but their performances deteriorate dramatically as the frequency changes.As the range of w...Most reported electromagnetic wave absorption(EWA)materials show significant effective absorption in a certain frequency range,but their performances deteriorate dramatically as the frequency changes.As the range of working frequencies for electronic devices is gradually widening,it is of great interest to explore frequency-insensitive EWA materials that can achieve efficient absorption in every waveband by simply changing the absorption thickness.To this end,a multi-scale absorber(Fe/Fe_(3) C@NC)is rationally synthesized by chemical foaming and in-situ growth strategy.By controlling the growth of carbon nan-otubes,the Fe/Fe_(3) C@NC-2 exhibits a well-constructed 3D multi-scale architecture.Thanks to dipole po-larization,interface polarization and magnetic-dielectric energy conversion,the Fe/Fe_(3) C@NC-2 overcomes the frequency dispersion behavior and keeps a stable dielectric attenuation capability across the entire frequency range.Consequently,it delivers a superb full-band absorption of-50.1,-59.83,-55.87 and-51.91 dB in the S,C,X and Ku bands,respectively.The maximum radar cross-sectional reduction reaches 35.44 dB m^(-2) when the incidentθis 20°,testifying its impressive performance.Surprisingly,this EWA material also shows a remarkable resistance to oxidation and corrosion derived from the tightly coated carbon layers.This work provides new insight into the design of multi-band and stable EWA materials for practical application.展开更多
基金This work was financially supported by the National Natural Science Foundation of China （Nos. 51102278, 51672049, 51602154 and 11575085）, Start-up Grant of Fudan University （No. JIJH2021001）, the Aeronautics Science Foundation of China （No. 2014ZF52072） and the Priority Academic Program Development of Jiangsu Higher Education Institutions （PAPD）.
文摘Exploring lightweight microwave attenuation materials with strong and tunable wideband microwave absorption is highly desirable but remains a significant challenge. Herein, three-dimensional （3D） porous hybrid composites consisting of NiFe nanoparticles embedded within carbon nanocubes decorated on graphene oxide （GO） sheets （NiFe@C nanocubes@GO） as high-performance microwave attenuation materials have been rationally synthesized. The 3D porous hybrid composites are fabricated by a simple method, which involves one-step pyrolysis of NiFe Prussian blue analogue nanocubes in the presence of GO sheets. Benefiting from the unique structural features that exhibit good magnetic and dielectric losses as well as a proper impedance match, the resulting NiFe@C nanocubes@GO composites show excellent microwave attenuation ability. With a minimum reflection loss （RL） of -51 dB at 7.7 GHz at a thickness of 2.8 mm and maximum percentage bandwidth of 38.6% for RL 〈 -10 dB at a thickness of 2.2 mm, the NiFe@C nanocubes@GO composites are superior to the previously reported state-of-the-art carbon-based microwave attenuation materials.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51407134 and 52002196)the Natural Science Foundation of Shandong Province(Nos.ZR2019YQ24 and ZR2020QF084)+2 种基金the Taishan Scholars and Young Experts Program of Shandong Province(No.tsqn202103057)the Qingchuang Talents Induction Program of Shandong Higher Education Institution(Research and Innovation Team of Structural-Functional Polymer Composites)the Special Financial of Shandong Province(Structural Design of High-efficiency Electromagnetic Wave-absorbing Composite Materials and Construction of Shandong Provincial Talent Teams(No.37000022P990304116449)).
文摘To achieve excellent electromagnetic wave(EMW)absorption properties,the microstructure design of the absorber is critical.In this work,six kinds of N-Ni/C nanostructures with different morphologies were prepared by one-step hydrothermal method and high temperature carbonization by adjusting the types of nickel salts and reaction solvents.The EMW absorption performance of six different morphologies of N-Ni/C nanostructures was compared and analyzed.Among them,it is found that the nanoflowerlike N-Ni/C composite has excellent dielectric loss and magnetic loss synergistic effect due to its polycrystalline structure,and can obtain excellent EMW absorption performance.The minimum reflection loss value at a thickness of 1.9 mm is-59.56 dB at 16.88 GHz,and the effective absorption bandwidth value reaches 6.0 GHz at a thickness of 2.2 mm.Our research shows that different morphologies and multiple lattice structures of nanostructures with the same composition have a significant influence on EMW absorption performance,which provides new research ideas for developing high-performance EMW absorbing materials.
基金supported by the Fund of Fok Ying Tung Education Foundation,the Major Research Project of innovative Group of Guizhou province(No.2018-013)the National Science Foundation of China(Nos.11604060 and 11964006)the Foundation of the National Key Project for Basic Research(No.2012CB932304).
文摘Impedance matching characteristics and loss capabilities including magnetic loss,polarization loss and conduction loss are critical factors to improve microwave absorption performances(MAPs).To elevate these aspects,herein,yolk-shell structured CoNi@Air@C/SiO_(2)@Polypyrrole(PPy)magnetic multicomponent nanocubes(MCNCs)were designed and successfully fabricated in high efficiency through a continuous co-precipitation route,classical Stöber method,thermal treatment and polymerization reaction.The obtained results indicated that the formation of SiO_(2) effectively stabilized the cubic geometrical morphology and yolk-shell structure during the high-temperature pyrolysis process.The introduction of PPy greatly boosted their polarization loss and conductive loss capabilities.Therefore,the as-prepared yolkshell structured CoNi@Air@C/SiO_(2)@PPy MCNCs presented superior MAPs compared to CoNi@Air@C/SiO_(2) MCNCs.Furthermore,by regulating the content of PPy,the obtained CoNi@Air@C/SiO_(2)@PPy MCNCs displayed tunable and excellent comprehensive MAPs in terms of strong absorption capabilities,broad frequency bandwidths and thin matching thicknesses,which could be ascribed to the unique structure and excellent magnetic-dielectric synergistic effect.Therefore,our findings provided an alternative pathway to effectively utilize the magnetic-dielectric synergy and loss capabilities for the developing yolk-shell structured magnetic MCNCs as the strong wideband microwave absorbers.
基金financially supported by the National Natural Science Foundation of China (No. 50972119 and 51002120)the 111 Project (No. B08040)the fund of the State Key Laboratory Of Solidification Processing in Northwestern Polytechnical University (No. KB200920)
文摘The dielectric and electromagnetic properties of two types of SiC fibres with different compositions were investigated. The permittivity and electromagnetic shielding effectiveness （SE） of SiC fibre bundles were measured in 8.2-12.4 GHz by waveguide method. The reflection coefficient （RC） of unidirectional SiC fibre laminates was determined in 8-18 GHz using naval research laboratory （NRL）-arc method. Results showed that the electromagnetic wave （EMW） absorbing properties of SiC fibres were correlated with their composition, microstructure and instinct performance of electrical resistance. SiC fibres with higher content and greater size of nano-scale H-SiC showed higher permittivity, conductivity, SE and lower RC, which resulted in their better EMW absorbing ability, Le. the lower reflection to EMW.
基金financially supported by the Natural Science Foundation of Jiangsu Province(No.BK20221336)the Jiangsu Agricultural Science and Technology Independent Innovation Fund(No.CX(20)3041)+2 种基金the National Natural Science Foundation of China(No.31971740)the Research Project of the Jiangxi Forestry Bureau(No.202134)the Nanping Science and Technology Planning Project(No.2020Z001)。
文摘Growing electromagnetic pollution has plagued researchers in the field of electromagnetic(EM)energy dissipation for many years;it is increasingly important to solve this problem efficiently.Metal-organic frameworks(MOFs),a shining star of functional materials,have attracted great attention for their advantages,which include highly tunable porosity,structure,and versatility.MOF-derived electromagnetic wave(EMW)absorbers,with advantages such as light weight,thin matching thickness,strong capacity,and wide effective bandwidth,are widely reported.However,current studies lack a systematic summary of the ternary synergistic effects of the precursor component-structure-EMW absorption behavior of MOF derivatives.Here we describe in detail the electromagnetic(EM)energy dissipation mechanism and strategy for preparing MOF-derived EMW absorbers.On the basis of this description,the following means are suggested for adjusting the EM parameters of MOF derivatives,achieving excellent EM energy dissipation:(1)changing the metal and ligands to regulate the chemical composition and morphology of the precursor,(2)controlling pyrolysis parameters(including temperature,heating rate,and gas atmosphere)to manipulate the structure and components of derivatives,and(3)compounding with enhancement phases,including carbon nanomaterials,metals,or other MOFs.
基金the National Natural Science Foundation of China(52102361,62071239)Natural Science Foundation of Jiangsu Province(BK20200827)+1 种基金National Key Laboratory on Electromagnetic Environmental Effects and Electro-optical Engineering(JCKYS2022LD2)the Startup Foundation for Introducing Talent of NUIST。
文摘The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal–organic frameworks(MOFs)and graphene oxide(GO)building blocks that exhibit an ultralow density and uniformly distributed MOFs on GO sheets is important for various applications.Herein,we report a facile route for synthesizing MOF/reduced GO(rGO)aerogels based on the gelation of GO,which is directly initiated using MOF crystals.Free metal ions exposed on the surface of MIL-88A nanorods act as linkers that bind GO nanosheets to a three-dimensional porous network via metal–oxygen covalent or electrostatic interactions.The MOF/rGOderived magnetic and dielectric aerogels Fe_(3)O_(4)@C/rGO and Ni-doped Fe_(3)O_(4)@C/rGO show notable microwave absorption(MA)performance,simultaneously achieving strong absorption and broad bandwidth at low thickness of 2.5(-58.1 dB and 6.48 GHz)and 2.8 mm(-46.2 dB and 7.92 GHz)with ultralow filling contents of 0.7 and 0.6 wt%,respectively.The microwave attenuation ability of the prepared aerogels is further confirmed via a radar cross-sectional simulation,which is attributed to the synergistic effects of their hierarchically porous structures and heterointerface engineering.This work provides an effective pathway for fabricating hierarchically porous MOF/rGO hybrid aerogels and offers magnetic and dielectric aerogels for ultralight MA.
文摘3D reticulated ceramics (3DRCs) with the composition containing SrFe12O19-SiC-TiO2 were prepared by a replication process with polyurethane sponges as the template in ceramic slurry. The electrical conductivity, dielectric and magnetic parameters of 3D reticulated ceramics (3DRCs) were measured with changes in cell size of the sponges, contents in the slurry and sintering temperature in this paper. Discussions about the influential factors of those parameters were focused on their electrical conductivity. The experimental results indicated that the electrical conductivity of 3DRCs raised with the increase of cell size, SiC/SrO 6Fe2O3 with weight ratio and sintering temperature. X-ray diffractions and SEM were used to investigate the relationship between electrical conductivity and sintering temperature. Deoxidizing reactions of SrO 6Fe2O3 caused the increasing electrical conductivity. The real part of permittivity (ε') and imaginary part of permeability (μ') raised with the increase of electrical conductivity (σ). The imaginary part of permittivity (ε') has a maximum at 10o S/cm with the increase of a, and the real part of permeability (μ') changes slightly with the increase of a. When a is at the range of 10-4 S/cm to 10o S/cm (a semi conductive state), both the imagine part of permittivity and permeability raises with increasing a, therefore, the 3DRCs present their high electromagnetic loss properties.
基金supported by the Fund of the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University,China (No. KP200901)
文摘Microwave absorbing properties of the carbonyl iron particles filled epoxy-silicone resin coatings showed visible degression when the coatings were heat treated at 300 ℃ with different time.The complex permittivity and permeability of the coatings before and after heat treatment were measured.After heat treatment at 300 ℃,the real part of permittivity of the coatings increased with increasing treatment time and showed frequency dependence dielectric response.The complex permeability showed remarkable variation while the resonance frequency of the coatings heat treated at 300 ℃ shifted from 7 to 12 GHz.The electromagnetic results indicated that microwave absorbing properties of the coatings showed more dependent on the complex permeability.The results showed that the difference of the electromagnetic and microwave absorbing properties before and after heat treatment was mainly attributed to the crystalline state transition of carbonyl iron particles.
基金the funding support from the startup fund of the Ohio State University(OSU),OSU Sustainability Institute Seed Grant,and OSU Institute for Materials Research Kickstart Facility Grantthe National Natural Science Foundation of China(No.31971740)+1 种基金Science and technology project of Jiangsu Province(BE2018391)the Open Fund from Henan University of Science and technology。
文摘Materials that can absorb electromagnetic(EM)wave have garnered increased attention in recent years due to their potential to mitigate the ever increasing environmental pollution by EM waves.Thanks to recent advances in micro/nanofabrication,a variety of magnetic metal-based EM absorbers have been reported.The design and synthesis of EM absorbers that exhibit efficient and wide-band absorption at small thicknesses,however,remains elusive.Here we report the design of fibrous nanostructures consisting of magnetic iron(Fe)nanoparticles and carbon nanotubes(CNTs),which exhibits a wide-band EM absorption(3.8 GHz)while maintain the thickness at 1.2 mm.In our work,we created a novel core-shell structure by immersing the highly fibrous CNT-Fe structure into solid-state silicon(SiO)matrix.Finally,the SiO-coated CNT-Fe structures exhibit good stability against air-induced oxidation and acid corrosion while maintaining high EM absorption.Overall,the results reported in this study present new avenues to absorb EM from ambient air.We believe that our work elevates the utility of EM absorbers to real-world applications such as anti-acid and oxidation ability.
基金Project supported by the Science and Engineering Research Board(SERB)New Delhi,India(SR/FTP/PS-068/2014)
文摘Copper and rare earth-doped(RE = La, Gd, Nd) CuFe1.85RE0.15O4nano ferrites were prepared using the so nochemical method. The effective doping of rare-earth(La3+, Nd3+, Gd3+) ions with copper nanoferrites was confirmed by X-ray diffraction. The tetrahedral and octahedral sites of the nano ferrites were identified through the Fourier transform infrared spectra. The doping of rare-earth elements enhances the optical bandgap energy of the nanoferrites that are observed through Ultraviolet-DRS spectra. The oxidation state of the elements Cu 2 p, La 3 d, Nd 3 d, Gd 3 d, Fe 2 p and O 1 s was analyzed. Scanning electron microscopy images indicate a spherical morphology with agglomeration to some elongate. The values of dielectric constant and conductivity decrease considerably due to doping rare-earth ions in copper nanoferrites. Low saturation magnetization and high coercivity values of rare earth-doped copper nanoferrites are observed from the typical hysteresis curves.
基金supported by the National Natural Science Foundation of China(Nos.52103334,52071053,and U1704253)China Postdoctoral Science Foundation(Nos.2020M680946,2020M670748)the Fundamental Research Funds for the Central Universities(No.DUT20GF111).
文摘Metamaterials are widely used in electromagnetic radiation and camouflage for their flexible wavefront manipulation and polarization over a broad spectrum ranging from microwaves to optics.However,multispectral compatible camouflage faces significant challenges due to tremendous scale differences of unit cells and desired radiative properties in various spectral regimes.This study assembles a micron-scale infrared emitter,a millimeter-scale microwave absorber,and a metal reflector to propose a hierarchical metamaterial that reduces microwave scattering and reflects low-infrared waves.As a proof of concept,laser etching micro-manufactures an upper infrared shielding layer with a periodic metal pattern.At the same time,bottom square frustum metastructure composites are fabricated and optimized based on genetic algorithms.Under the normal incidence transverse electromagnetic wave with a 90°azimuth angle,the hierarchical strategy and infrared unit create an asymmetric electric field distribution of local near-field coupling,which is conducive to generating additional resonance for broadening the absorption bandwidth.Experiments verify the multispectral camouflage,which shows a high absorption efficiency of more than 90%,ranging from 3.6 to 6.2 and from 8.4 to 18 GHz with a total thickness of 4.05 mm(0.049λmax).Due to the non-reflection of surrounding thermal signals in the infrared 2-22μm region,low-infrared emissivity(0.29)metamaterials can adapt to various thermal backgrounds.This methodology can provide a novel route for fabricating multispectral camouflage devices.
基金Project supported by the National Natural Science Foundation of China (Grant No. 52088101)the Kunpeng Plan of Zhejiang ProvinceNingbo Top Talent Program。
文摘Saturation magnetization,magneto-crystalline anisotropy field,and dielectric properties are closely related to microwave devices applied at different frequencies.For regulating the magnetic and dielectric properties of W-type barium ferrites,single-phase BaMe_(2)Fe_(16)O_(27)(Me=Fe,Mn,Zn,Ni,Co) with different Me ions were synthesized by the high-temperature solid-state method.The saturation magnetization(Ms) range from 47.77 emu/g to 95.34 emu/g and the magnetic anisotropy field(H_a) range from 10700.60 Oe(1 Oe=79.5775 A·m^(-1)) to 13739.57 Oe,depending on the type of cation substitution in the hexagonal lattice.The dielectric permittivity and dielectric loss decrease with increasing frequency of the AC electric field in the low-frequency region,while they almost remain constant in the high-frequency region.The charac teristics of easy regulation and preparation make it a potential candidate for use in microwave device applications.
文摘In this work,the magnetic,dielectric properties and electric modulus of Ce^(3+) substituted cobaltmagnesium(Co_(0.7)Mg_(0.3)Ce_(x)Fe_(2-x)O_4)(labeled as CMCF) ferrite nanoparticles were investigated in detail.Saturation magnetization decreases from 50.05 to 34.87 emu/g for further substituting Ce^(3+) ions.Meanwhile,coercivity increases from 738.22 Gs for the CMCFO sample to 912.10 Gs for the CMCF2 sample,then decreases monotonically to 762.1 Gs for the CMCF5 sample.The cerium content and particle size play important roles in controlling the magnetization and coercivity of the CMCF nanoparticles.All CMCF nanoferrites are suitable for microwave applications since their high-frequency response ranges from 7.72 to 11.07 GHz.The CMCF nanoferrites' dielectric parameter dispersion exhibits normal behavior.The pristine Co-Mg nanoferrite only has ε' value of 28.25,but the nanoferrite MCMF2 has ε' value of365.03,with an enhancing ratio of 1192%.The conduction mechanism of the MCMF nanoferrites was determined by fitting the σ_(ac) results via the Jonscher power law.At 653 K,large polaron tunnelling is thought to be responsible for this conduction process,which is followed by electron barrier hopping at higher temperatures.Cole-Cole diagrams at different temperatures,assuring the contributions of the grains and their boundaries at lower temperatures(653 K) and only the grains at higher temperatures.Based on our results,the CMCF nanoferrites hold magnetic and semiconducting nature,which can be used in magnetic devices and dielectrics in lower-frequencies or conductors in higher-frequencies.
基金support from the National Natural Science Foundation of China(No.52073039)Major Special Projects of Sichuan Province(Nos.2019ZDZX0027 and 2019ZDZX0016).
文摘The combination of high efficiency and environmental stability is vital to promote the commercial appli-cations of microwave absorption(MA)materials,yet remains challenging in the absence of facile routes.Here,we put forward a graphene-reinforced construct approach for one-pot synthesis of 3D intercon-nected magnetic-dielectric frameworks via pre-functionalization and subsequent assembly.Multiple in-teractions among discrete precursors are capable of manipulating the confined growth and interfacial self-assembly.Significant enhancements in MA properties are triggered in a straightforward manner us-ing ultralow feeding fractions of graphene oxide nanosheet.The minimum reflection loss is up to-60.1 dB(99.9999%wave absorption)and the effective absorption bandwidth reaches 5.9 GHz(almost covering the Ku band).Remarkably,based on the optimization by ultralow concentrations of graphene,the as-prepared nanoarchitecture simultaneously integrates strong absorption,broad bandwidth,and low matching thick-ness.The embedded graphene nanosheets serve as high-speed electron transmission channels and hollow resonance cavities,facilitating multimode attenuations and impedance-matching characteristics.Mean-while,the graphene-reinforced framework suppresses the corrosion of magnetic components,whose cor-rosion rate reduces by an order of magnitude.This study provides a simple procedure to boost magnetic-dielectric absorbers for comprehensive MA performances and enhanced corrosion resistance.
基金supported by the National Natural Science Foundation of China(No.52172213).
文摘Aerogel-based composites hold promising application prospects as potential electromagnetic wave(EMW)absorption materials,yet the construction of such materials with ingenious microstructures,appropriate magnetic/dielectric multi-components,and integrated multifunctionality remains considerably challenging.Herein,a multicomponent Co/MnO/Ti_(3)C_(2)Tx MXene/rGO(CMMG)hybrid aerogel featured with three-dimensional(3D)vertical directional channel architecture is reported.Benefiting from the synergistic effect arising from the 3D conductive networking structure,diverse heterogeneous interfaces,magnetic/dielectric multicomponent,and multiple loss pathways,the optimized CMMG-2 aerogel delivers fascinating EMW absorption capabilities,characterized by a minimal reflection loss(RL_(min))of-77.41 dB and an effective absorption bandwidth(EAB)of 6.56 GHz.Additionally,the remarkable hydrophobicity,exceptional thermal insulation capabilities,and outstanding photothermal properties of CMMG-2 aerogel make it highly promising for multiple application in diverse and demanding environments.Interestingly,the distinctive pore structure of hybrid aerogel also allows it for sensitive and reliable detection of electrical signals caused by pressure changes and human motion.Thus,this research provides a viable design strategy for the development of lightweight,efficient,and multifunctional aerogel-based EMW absorption materials for various application scenarios.
基金financially supported by the Natural Science Foundation of Liaoning Province(No.2014020094)the Key Laboratory Construction Fund of Shenyang(No.F14187-1-00)
文摘The spinel cobalt chromium zinc ferrites（Co0.7Cr0.1Zn0.2Fe2O4） and the polyaniline（PANI）-Co0.7Cr0.1Zn0.2Fe2O4 composites were prepared by polyacrylamide gel and an in situ polymerization method,respectively.The structure of the synthesized material was characterized by X-ray diffraction（XRD） and Fourier transform infrared spectrometer（FTIR）,which shows that the spinel Co0.7Cr0.1Zn0.2Fe2O4 ferrites and the PANI Co0.7Cr0.1Zn0.2Fe2O4 composites are obtained.As a small amount of Co^2＋ in the octahedron ferrite is replaced by Cr^3＋,the lattice constant of Co0.8Cr0.2Zn0.2Fe2O4 ferrites reduces from0.8409 to 0.8377 nm.The magnetic properties of the two materials were investigated by vibrating sample magnetometer（VSM）.The VSM results confirm that the saturation magnetization（Ms）,remanent magnetization（Mr） and coercive force（Hc） of the PANI-Co0.7Cr0.1Zn0.2Fe2O4composites are 8.80 mA·m^2·g^-1,3.14 mA·m^2·g^-1 and37.22 kA·m^-1,respectively,which are smaller than those of the Co0.7Cr0.1Zn0.2Fe2O4 ferrites.The microwave absorbing capability of the two materials was studied by waveguide method.In the frequency range of 5-20 GHz,two reflection loss maximum values of the PANI-Co0.7Cr0.1Zn0.2Fe2O4 composites appear at 14.1 and 17.9 GHz with-13.17 and-15.36 dB,respectively,which are obviously higher than those of the Co0.7Cr0.1Zn0.2Fe2O4 ferrites.
基金This work was supported by the National Natural Science Foundation of China under Grant No.60371020.
文摘The scattered field and differential scattered section （DSS） of a moving spherical particle with a high speed are investigated numerically. The coordinate and vector transformations are used to establish a theoretical basis for studying the laser scattering of a moving particle. The DSS of a moving spherical particle is explained by the electric and magnetic field from Mie scattering theory. Assuming the laser wavelength of 1.06μ m, we compute the ratio of the laser DSS of the moving dielectric spherical particle to that of the static dielectric spherical particle, which changes with radii, speeds and scattering angles of the particle. The numerical results show that the laser DSS of the moving spherical particle is tightly connected with its speed and scattering zenith angle. If a spherical particle moves with high speed, the laser DSS due to movement of the particle could not be neglected. If the speed of the dielectric spherical particle is fluctuating, the Doppler effect and the frequency spectrum expansion play important roles.
基金Kamala Institute of Technology and Science for their support and encouragementCSIR-New Delhi for providing financial assistance (09/132 (0879)/2018-EMR-1)+1 种基金CSIR-New Delhi for providing financial assistanceCMR College of Engineering and Technology for their support and encouragement。
文摘In the present study,rare earth samarium(Sm^(3+))substituted Ni-Cu spinel ferrites with the composition of Ni_(0.1)Cu_(0.9)Sm_(x)Fe_(2-x)O_(4)(0≤x≤0.05 in steps of 0.01)were synthesized by using the citrate induced sol-gel auto combustion technique.These ferrites'structural,optical,magnetic,and dielectric studies were carried out using X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),field emission scanning electron microscopy(FESEM),ultraviolet-visible(UV-vis),a vibrational sample magnetometer(VSM),and an LCR meter.The pure Ni-Cu ferrite exhibits a tetragonal structure owing to the presence of the John Tellar ion(Cu^(2+)).XRD patterns confirm that the tetragonal structure gradually transforms into the cubic spinel structure with samarium substitution.The nano-scale structures of these ferrites were confirmed by the average crystallite size(10.11-20.99 nm)derived from the X-ray diffraction patterns,and grain size(42.60-83.36 nm)assessed from FESEM photographs.The existence of elements according to their chemical composition was verified by using energy dispersive X-ray(EDX)spectra.The absorption bands(v_(1) and v_(2))detected in FTIR transmission spectra below the wavenumber of 600 cm^(-1)reveal the stretching vibrations of M-O bonds in the spinel structure at tetrahedral and octahedral locations.The band gap ene rgy obtained from UV absorption reveals the semiconducting nature of the samples.The high saturation magnetization(M_(s))is noticed at 15 K temperature for x=0.02 composition as 32.98 emu/g,while at 300 K for x=0.01composition as 27.61 emu/g.The suggested cation distribution is in good agreement with observed and predicted magnetic moment values at 300 K.The expected behavior of ferrites reveals the observed dielectric constant,loss tangent,and ac-conductivity values in the frequency range of 20 Hz-20 MHz.Cole-Cole plots confirm that the impedance contribution is attributed to grain boundaries.
基金financially supported by the National Natu-ral Science Foundation of China(Grant Nos.22178384,22238012 and 52002363)the Science Foundation of China University of Petroleum,Beijing(Grant No.ZX20220079)the Aeronautical Science Foundation of China(Grant No.2020Z054025002).
文摘Most reported electromagnetic wave absorption(EWA)materials show significant effective absorption in a certain frequency range,but their performances deteriorate dramatically as the frequency changes.As the range of working frequencies for electronic devices is gradually widening,it is of great interest to explore frequency-insensitive EWA materials that can achieve efficient absorption in every waveband by simply changing the absorption thickness.To this end,a multi-scale absorber(Fe/Fe_(3) C@NC)is rationally synthesized by chemical foaming and in-situ growth strategy.By controlling the growth of carbon nan-otubes,the Fe/Fe_(3) C@NC-2 exhibits a well-constructed 3D multi-scale architecture.Thanks to dipole po-larization,interface polarization and magnetic-dielectric energy conversion,the Fe/Fe_(3) C@NC-2 overcomes the frequency dispersion behavior and keeps a stable dielectric attenuation capability across the entire frequency range.Consequently,it delivers a superb full-band absorption of-50.1,-59.83,-55.87 and-51.91 dB in the S,C,X and Ku bands,respectively.The maximum radar cross-sectional reduction reaches 35.44 dB m^(-2) when the incidentθis 20°,testifying its impressive performance.Surprisingly,this EWA material also shows a remarkable resistance to oxidation and corrosion derived from the tightly coated carbon layers.This work provides new insight into the design of multi-band and stable EWA materials for practical application.
