Some theoretic problems of gyrotron pump for free electron laser with electro- magnetic wiggler(EMW-FEL)are studied,such as the azimuthal polarization of EMW,and the relation between the transient properties of gyrotr...Some theoretic problems of gyrotron pump for free electron laser with electro- magnetic wiggler(EMW-FEL)are studied,such as the azimuthal polarization of EMW,and the relation between the transient properties of gyrotron and the working conditions.These prob- lems make a remarkable influence on EMW-FEL system.In this paper,the numerical calcula- tions and analysis are given for TE_13 mode.展开更多
Metal foams are a fascinating group of materials that possess distinct physicochEMIcal properties and interconnected strut features with high surface area-to-volume ratios, high specific strength and lightweight natur...Metal foams are a fascinating group of materials that possess distinct physicochEMIcal properties and interconnected strut features with high surface area-to-volume ratios, high specific strength and lightweight nature. These characteristics make them ideal for applications in vibration damping, heat insulation and weight reduction. In recent years, there has been increasing interest in the application of interfering energy conversion such as electromagnetic wave (EMW) and sound, where the metal foams could emerge as a solution. This paper will present a comprehensive review of the preparation methods as well as the interference energy converting mechanisms for metal foams. Typically, the progress and prospective aspects of metal foams for EMW absorption, electromagnetic interference (EMI) shielding and sound absorption have been emphasized. Through this review, we aspire to offer valuable insights for the development of multifunctional applications with metal foam materials.展开更多
The rapid advancement of lightweight and high-power electronic devices has led to increasingly aggravated issues of electromagnetic wave(EMW)interference and heat accumulation,which severely threaten the stability and...The rapid advancement of lightweight and high-power electronic devices has led to increasingly aggravated issues of electromagnetic wave(EMW)interference and heat accumulation,which severely threaten the stability and service life of these devices.To address these challenges,we propose a simple and scalable mechanochemical strategy to activate hexagonal boron nitride flakes(BNFs)via liquid metal(LM),which results in outstanding EMW absorption and high thermally conductive capabilities.This facile modification approach avoids multistep reactions,high solvent consumption,and high energy input while simultaneously introducing abundant interfacial polarization centers,thus optimizing the EMW absorption performance of BNFs.Consequently,the optimized BNF@LM composites exhibit remarkable EMW absorption with a minimum reflection loss(RLmin)of-48.4 dB and a maximum effective absorption bandwidth(EAB_(max))of 5.76 GHz.In addition,coupling the H-BNF@LM composites with aramid nanofibers(ANFs)can impart ANF-based films with good thermal conductivity and flexibility,making them suitable for flexible electronic devices.Typically,the H-BNF@LM/ANF films can reach a thermal conductivity of 0.54 W·m^(-1)·K^(-1),as measured via the hot wire method,which is nearly 5 times greater than that of the ANF film(0.10 W·m^(-1)·K^(-1)).Moreover,the H-BNF@LM/ANF films can effectively attenuate incident EMW and exhibit remarkable flame retardancy,endowing them with strong adaptability to extreme environment.展开更多
As a lot of electromagnetic pollution and interference issues have emerged,to overcome electromagnetic interference,prevent electromagnetic hazards,and develop new high-performance electromagnetic wave(EMW)absorbers h...As a lot of electromagnetic pollution and interference issues have emerged,to overcome electromagnetic interference,prevent electromagnetic hazards,and develop new high-performance electromagnetic wave(EMW)absorbers have become a significant task in the field of materials science.In this paper,a three-dimensional(3D)carbon nanofibers network with core-shell structure,embedded with varied molar ratios of iron and cobalt(4:0,3:1,2:2,1:3,0:4),was effectively synthesized(Fe/Co@C-CNFs)via electrospinning.The phase,microstructure,magnetic and EMW absorption properties were studied.It is discovered that Fe/Co@C-CNFs doped with iron:cobalt=1:1 have excellent EMW absorption capacity.When the matching thickness is 1.08 mm,the minimum reflection loss(RL)value is-18.66 dB,while the maximum effective absorption bandwidth(EAB)reaches 4.2 GHz(13.9-18 GHz)at a thickness of 1.22 mm.This is owing to the absorbers'superior impedance matching and multiple reflections as well as the conductivity,dielectric,and magnetic losses of carbon nanofibers embedded with Fe-Co alloy particles.In addition,the radar cross section(RCS)of the absorbers has been calculated by CST Studio Suite,showing that the absorbing coating can effectively reduce the RCS at various angles,especially for Fe/Co@C-CNFs doped with iron:cobalt=1:1.These findings not only provide new insights for the preparation of light-weight and high-performance electromagnetic wave absorbers,but also contribute to energy storage and conversion.展开更多
To tackle the aggravating electromagnetic wave(EMW)pollution issues,high-efficiency EMW absorption materials are urgently explored.Metal-organic framework(MOF)derivatives have been intensively investigated for EMW abs...To tackle the aggravating electromagnetic wave(EMW)pollution issues,high-efficiency EMW absorption materials are urgently explored.Metal-organic framework(MOF)derivatives have been intensively investigated for EMW absorption due to the distinctive components and structures,which is expected to satisfy diverse application requirements.The extensive developments on MOF derivatives demonstrate its significantly important role in this research area.Particularly,MOF derivatives deliver huge performance superiorities in light weight,broad bandwidth,and robust loss capacity,which are attributed to the outstanding impedance matching,multiple attenuation mechanisms,and destructive interference effect.Herein,we summarized the relevant theories and evaluation methods,and categorized the state-of-the-art research progresses on MOF derivatives in EMW absorption field.In spite of lots of challenges to face,MOF derivatives have illuminated infinite potentials for further development as EMW absorption materials.展开更多
NiFe_(2)O_(4)/polypyrrole(NiFe_(2)O_(4)/PPy)nanocomposites are prepared by a simple surface-initiated polymerization method and demonstrate negative permittivity in the low frequency regions.These nanocomposites also ...NiFe_(2)O_(4)/polypyrrole(NiFe_(2)O_(4)/PPy)nanocomposites are prepared by a simple surface-initiated polymerization method and demonstrate negative permittivity in the low frequency regions.These nanocomposites also exhibit significantly enhanced electromagnetic wave(EMW)absorption property in the high frequency regions.Compared with pure PPy,the enhanced negative permittivity is observed in the NiFe_(2)O_(4)/PPy nanocomposites with a NiFe_(2)O_(4)loading of 5.0,10.0,20.0 and 40.0 wt%,indicating the formation of metal-like electrical conducting network in NiFe_(2)O_(4)/PPy nanocomposites.Moreover,the negative permittivity could be tuned by changing the NiFe_(2)O_(4)loading.The minimum reflection loss(RL)of-40.8 dB is observed in the 40.0 wt%NiFe_(2)O_(4)/PPy composites with a thickness of only 1.9 mm.The effective absorption bandwidth below-10.0 and-20.0 dB reaches 6.08 and 2.08 GHz,respectively.The enhanced EMW absorption performance benefits from the improved independence matching,EMW attenuation capacity,and synergistic effects of conduction loss,dielectric loss(interfacial and dipole polarizations)and magnetic loss(exchange and natural resonances).This research work provides a guidance for the fabrication of nanocomposites with an excellent EMW absorption.展开更多
Biomass absorbing materials have received increasing attention for electromagnetic wave(EMW)absorption field absorbing materials due to its low density and high dielectric loss.However,the biomass EMW absorbing materi...Biomass absorbing materials have received increasing attention for electromagnetic wave(EMW)absorption field absorbing materials due to its low density and high dielectric loss.However,the biomass EMW absorbing materials often suffer from the insufficient magnetic loss and impedance matching.In this work,a facile ZIF-8/ZIF-67-derived biomass composites(CoZnO@BPC)was prepared for high-performance EMW absorption based on multi-component micro,nano structures metal particles and xanthoce sorbifolia bunge shells-derived biomass porous carbon(BPC).The dielectric loss and/or magnetic loss abilities of CoZnO@BPC composites were adjusted by changing the mass ratio of Zn^(2+)to Co^(2+)ions.Under the filled amount of 20 wt%,Co Zn O@BPC exhibited excellent EMW absorption with the minimum reflection loss(RL)at 15.84 GHz is-50.2 dB,and the matching thickness is only 1.7 mm.By adjusting the ZIFs mass ratio,the effective absorption bandwidth(EAB)can be up to 5.92 GHz(from 12.08 GHz to 18 GHz),and the matching thickness is only 1.9 mm.The results provide a new insight for the economical and efficient preparation of lightweight and advanced microwave absorbing materials.展开更多
Functional carbonaceous materials with controllable morphology,low apparent density,large surface area,and high porosity starting from natural precursors using environmentally friendly processes are an ap-pealing topi...Functional carbonaceous materials with controllable morphology,low apparent density,large surface area,and high porosity starting from natural precursors using environmentally friendly processes are an ap-pealing topic in the electromagnetic wave(EMW)field.In this work,renewable pine woods with ordered pore channels are selected to load highly dispersed CoFe alloy nanoparticles formed by in-situ pyrolysis reaction between Fe_(3)O_(4)nanospheres and ZIF-67 nanoparticles.The constructed three-dimensional(3D)porous CWA-CoFe-NC aerogel inherits the characteristics of highly dispersed small CoFe alloy nanopar-ticles,porous carbon aerogel with rectangular honeycomb-like structure,and abundant N heteroatoms.Therefore,CWA-CoFe-NC aerogel achieves an excellent EMW absorption performance with reflection loss(RL)values of−61.6 and−58.2 dB at matching thicknesses of 3.7 and 1.2 mm,respectively.Benefiting from the reasonable design of the composite structure and composition,3D porous aerogel also enables great potential for multifunctional applications.Particularly,good lightweight and mechanical properties are realized in the CWA-CoFe-NC aerogels due to their ordered pore channels and abundant rectangular pores.Furthermore,good flame retardant performance can ensure the serviceability of the target device in high/low-temperature environments.In addition,CWA-CoFe-NC aerogels show good thermal stability and thermal management characteristics.This work provides a novel and effective method for the prepa-ration of lightweight,high-performance,and multifunctional EMW absorbers.展开更多
基金Project supported by the National Natural Science Foundatioil of China and the National High Technology Plan(laser technology).
文摘Some theoretic problems of gyrotron pump for free electron laser with electro- magnetic wiggler(EMW-FEL)are studied,such as the azimuthal polarization of EMW,and the relation between the transient properties of gyrotron and the working conditions.These prob- lems make a remarkable influence on EMW-FEL system.In this paper,the numerical calcula- tions and analysis are given for TE_13 mode.
基金supported by the National Natural Science Foundation of China(No.52271180)the Leading Goose R&D Program of Zhejiang Province(2022C01110).
文摘Metal foams are a fascinating group of materials that possess distinct physicochEMIcal properties and interconnected strut features with high surface area-to-volume ratios, high specific strength and lightweight nature. These characteristics make them ideal for applications in vibration damping, heat insulation and weight reduction. In recent years, there has been increasing interest in the application of interfering energy conversion such as electromagnetic wave (EMW) and sound, where the metal foams could emerge as a solution. This paper will present a comprehensive review of the preparation methods as well as the interference energy converting mechanisms for metal foams. Typically, the progress and prospective aspects of metal foams for EMW absorption, electromagnetic interference (EMI) shielding and sound absorption have been emphasized. Through this review, we aspire to offer valuable insights for the development of multifunctional applications with metal foam materials.
基金National Natural Science Foundation of China(No.52372098)the Aeronautical Science Foundation of China(No.2024Z0550N8002)the Taishan Scholars Foundation of Shandong(No.Tsqnz20230628).
文摘The rapid advancement of lightweight and high-power electronic devices has led to increasingly aggravated issues of electromagnetic wave(EMW)interference and heat accumulation,which severely threaten the stability and service life of these devices.To address these challenges,we propose a simple and scalable mechanochemical strategy to activate hexagonal boron nitride flakes(BNFs)via liquid metal(LM),which results in outstanding EMW absorption and high thermally conductive capabilities.This facile modification approach avoids multistep reactions,high solvent consumption,and high energy input while simultaneously introducing abundant interfacial polarization centers,thus optimizing the EMW absorption performance of BNFs.Consequently,the optimized BNF@LM composites exhibit remarkable EMW absorption with a minimum reflection loss(RLmin)of-48.4 dB and a maximum effective absorption bandwidth(EAB_(max))of 5.76 GHz.In addition,coupling the H-BNF@LM composites with aramid nanofibers(ANFs)can impart ANF-based films with good thermal conductivity and flexibility,making them suitable for flexible electronic devices.Typically,the H-BNF@LM/ANF films can reach a thermal conductivity of 0.54 W·m^(-1)·K^(-1),as measured via the hot wire method,which is nearly 5 times greater than that of the ANF film(0.10 W·m^(-1)·K^(-1)).Moreover,the H-BNF@LM/ANF films can effectively attenuate incident EMW and exhibit remarkable flame retardancy,endowing them with strong adaptability to extreme environment.
基金financially supported by the National Natural Science Foundation of China(No.52272117)the National Key Research and Development Program of China(Nos.2022YFB3505104 and 2022YFB3706604)the Key Research and Development Program of Shandong Province(No.2022TSGC2322)。
文摘As a lot of electromagnetic pollution and interference issues have emerged,to overcome electromagnetic interference,prevent electromagnetic hazards,and develop new high-performance electromagnetic wave(EMW)absorbers have become a significant task in the field of materials science.In this paper,a three-dimensional(3D)carbon nanofibers network with core-shell structure,embedded with varied molar ratios of iron and cobalt(4:0,3:1,2:2,1:3,0:4),was effectively synthesized(Fe/Co@C-CNFs)via electrospinning.The phase,microstructure,magnetic and EMW absorption properties were studied.It is discovered that Fe/Co@C-CNFs doped with iron:cobalt=1:1 have excellent EMW absorption capacity.When the matching thickness is 1.08 mm,the minimum reflection loss(RL)value is-18.66 dB,while the maximum effective absorption bandwidth(EAB)reaches 4.2 GHz(13.9-18 GHz)at a thickness of 1.22 mm.This is owing to the absorbers'superior impedance matching and multiple reflections as well as the conductivity,dielectric,and magnetic losses of carbon nanofibers embedded with Fe-Co alloy particles.In addition,the radar cross section(RCS)of the absorbers has been calculated by CST Studio Suite,showing that the absorbing coating can effectively reduce the RCS at various angles,especially for Fe/Co@C-CNFs doped with iron:cobalt=1:1.These findings not only provide new insights for the preparation of light-weight and high-performance electromagnetic wave absorbers,but also contribute to energy storage and conversion.
基金This work was supported by the National Natural Science Foundation of China(No.51572157,No.21902085,and No.51702188)the Natural Science Foundation of Shandong Province(No.ZR2019QF012,No.ZR2019BEM024,ZR2016BM16)+3 种基金the Fundamental Research Funds of Shandong University(2018JC036,2018JC046,2018JC047)Qilu Young Scholar Program of Shandong(No.31370088963043)the Young Scholars Program of Shandong University(2018WLJH25)Key Technology Research and Development Program of Shandong(2019JZZY010312).
文摘To tackle the aggravating electromagnetic wave(EMW)pollution issues,high-efficiency EMW absorption materials are urgently explored.Metal-organic framework(MOF)derivatives have been intensively investigated for EMW absorption due to the distinctive components and structures,which is expected to satisfy diverse application requirements.The extensive developments on MOF derivatives demonstrate its significantly important role in this research area.Particularly,MOF derivatives deliver huge performance superiorities in light weight,broad bandwidth,and robust loss capacity,which are attributed to the outstanding impedance matching,multiple attenuation mechanisms,and destructive interference effect.Herein,we summarized the relevant theories and evaluation methods,and categorized the state-of-the-art research progresses on MOF derivatives in EMW absorption field.In spite of lots of challenges to face,MOF derivatives have illuminated infinite potentials for further development as EMW absorption materials.
基金supported by the Research Starting Foundation of Shaanxi University of Science and Technology(Program No.2019QNBJ-01)the Research Foundation for Thousand Young Talent Plan of Shaanxi province of China。
文摘NiFe_(2)O_(4)/polypyrrole(NiFe_(2)O_(4)/PPy)nanocomposites are prepared by a simple surface-initiated polymerization method and demonstrate negative permittivity in the low frequency regions.These nanocomposites also exhibit significantly enhanced electromagnetic wave(EMW)absorption property in the high frequency regions.Compared with pure PPy,the enhanced negative permittivity is observed in the NiFe_(2)O_(4)/PPy nanocomposites with a NiFe_(2)O_(4)loading of 5.0,10.0,20.0 and 40.0 wt%,indicating the formation of metal-like electrical conducting network in NiFe_(2)O_(4)/PPy nanocomposites.Moreover,the negative permittivity could be tuned by changing the NiFe_(2)O_(4)loading.The minimum reflection loss(RL)of-40.8 dB is observed in the 40.0 wt%NiFe_(2)O_(4)/PPy composites with a thickness of only 1.9 mm.The effective absorption bandwidth below-10.0 and-20.0 dB reaches 6.08 and 2.08 GHz,respectively.The enhanced EMW absorption performance benefits from the improved independence matching,EMW attenuation capacity,and synergistic effects of conduction loss,dielectric loss(interfacial and dipole polarizations)and magnetic loss(exchange and natural resonances).This research work provides a guidance for the fabrication of nanocomposites with an excellent EMW absorption.
基金financially supported by Natural Science Foundation of Fujian Province(Nos.2021T3024,2021H0017 and 2022H0016)。
文摘Biomass absorbing materials have received increasing attention for electromagnetic wave(EMW)absorption field absorbing materials due to its low density and high dielectric loss.However,the biomass EMW absorbing materials often suffer from the insufficient magnetic loss and impedance matching.In this work,a facile ZIF-8/ZIF-67-derived biomass composites(CoZnO@BPC)was prepared for high-performance EMW absorption based on multi-component micro,nano structures metal particles and xanthoce sorbifolia bunge shells-derived biomass porous carbon(BPC).The dielectric loss and/or magnetic loss abilities of CoZnO@BPC composites were adjusted by changing the mass ratio of Zn^(2+)to Co^(2+)ions.Under the filled amount of 20 wt%,Co Zn O@BPC exhibited excellent EMW absorption with the minimum reflection loss(RL)at 15.84 GHz is-50.2 dB,and the matching thickness is only 1.7 mm.By adjusting the ZIFs mass ratio,the effective absorption bandwidth(EAB)can be up to 5.92 GHz(from 12.08 GHz to 18 GHz),and the matching thickness is only 1.9 mm.The results provide a new insight for the economical and efficient preparation of lightweight and advanced microwave absorbing materials.
基金financially supported by the National Nat-ural Science Foundation of China(No.22269010)the Jiangxi Provincial Natural Science Foundation(No.20224BAB214021)+1 种基金the Major Research Program of Jingdezhen Ceramic Industry(No.2023ZDGG002)the Science Center for Gas Turbine Project(No.P2023-C-IV-002-001).
文摘Functional carbonaceous materials with controllable morphology,low apparent density,large surface area,and high porosity starting from natural precursors using environmentally friendly processes are an ap-pealing topic in the electromagnetic wave(EMW)field.In this work,renewable pine woods with ordered pore channels are selected to load highly dispersed CoFe alloy nanoparticles formed by in-situ pyrolysis reaction between Fe_(3)O_(4)nanospheres and ZIF-67 nanoparticles.The constructed three-dimensional(3D)porous CWA-CoFe-NC aerogel inherits the characteristics of highly dispersed small CoFe alloy nanopar-ticles,porous carbon aerogel with rectangular honeycomb-like structure,and abundant N heteroatoms.Therefore,CWA-CoFe-NC aerogel achieves an excellent EMW absorption performance with reflection loss(RL)values of−61.6 and−58.2 dB at matching thicknesses of 3.7 and 1.2 mm,respectively.Benefiting from the reasonable design of the composite structure and composition,3D porous aerogel also enables great potential for multifunctional applications.Particularly,good lightweight and mechanical properties are realized in the CWA-CoFe-NC aerogels due to their ordered pore channels and abundant rectangular pores.Furthermore,good flame retardant performance can ensure the serviceability of the target device in high/low-temperature environments.In addition,CWA-CoFe-NC aerogels show good thermal stability and thermal management characteristics.This work provides a novel and effective method for the prepa-ration of lightweight,high-performance,and multifunctional EMW absorbers.
