Carbonized melamine foam has been recognized as a promising material for microwave absorption due to its exceptional thermal stability,lightweight,and remarkable dielectric properties.In this study,we investigated the...Carbonized melamine foam has been recognized as a promising material for microwave absorption due to its exceptional thermal stability,lightweight,and remarkable dielectric properties.In this study,we investigated the impact of nitric acid oxidation on the surface of carbonized melamine foam and its microwave absorption properties.The treated foam exhibits optimal reflection loss of−21.51 dB at 13.20 GHz,with an effective absorption bandwidth of 7.04 GHz.The enhanced absorption properties are primarily attributed to the strengthened dielectric loss,improved impedance matching,and increased polarization losses resulting from the oxidized surfaces.This research demonstrates a promising new approach for research into surface treatments to improve the performances of microwave absorbers.展开更多
In this study,flower-like MoS2 constructed by nanosheets was synthesized by a simple hydrothermal method.The hydrothermal process was optimized and the effects of hydrothermal condition,including reaction temperature,...In this study,flower-like MoS2 constructed by nanosheets was synthesized by a simple hydrothermal method.The hydrothermal process was optimized and the effects of hydrothermal condition,including reaction temperature,reaction time and the ratio of Mo source to S source(Mo:S)in precursor,on microwave absorption performances and dielectric properties were investigated.Our results showed that when the reaction temperature was 180℃,the reaction time was 18 h,and the Mo:S was 1:3.5,the synthesized MoS2 had the best performance:Its minimum reflection loss could reach-55.78 dB,and the corresponding matching thickness was 2.30 mm with a wide effective bandwidth of 5.17 GHz.Further researches on the microwave absorption mechanism revealed that in addition to the destructive interference of electromagnetic waves,various polarization phenomena such as defect dipole polarization were the main reasons for microwave loss.We believe that MoS2 is a candidate for a practical microwave absorbent.展开更多
In this work,porous carbon particles were prepared from wheat flour by pyrolysis and activation.Through the subsequent coprecipitation and electroless plating,the surface and pores of carbon particles were modified by...In this work,porous carbon particles were prepared from wheat flour by pyrolysis and activation.Through the subsequent coprecipitation and electroless plating,the surface and pores of carbon particles were modified by nickel-rich particles with different morphologies.Several loss mechanisms,including dielectric loss,magnetic loss,multiple reflection and scattering loss,were used to assess the attenuation ability to incident electromagnetic waves of these composite particles.The result shows that the chain-shaped morphology of nickel can provide the highest dielectric loss.Under the filler loading of 20 wt.%,the minimum reflection loss(RL min)reached-38.42 dB at 13.2 GHz,and the_(max)imum effective absorption bandwidth(EAB_(max))was 5.2 GHz with a matching thickness of 2 mm.The excellent performance of the composite particles is attributed to the synergistic effect of outstanding impedance matching and supe-rior electromagnetic loss ability caused by the chain structure.The result shows that the morphology of modifiers in carbon-based composites is important to improve microwave absorption performance,and this work provides inspiration for the design of high-performance porous carbon-based composites.展开更多
The Co2FeSi films are deposited on Si （100） substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to sample posi...The Co2FeSi films are deposited on Si （100） substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe-330 Oe （1 Oe = 79.5775 A.m ^-1）, and low coercivities in a range of 5 Oe-28 Oe. As a result, high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co2FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.展开更多
Electromagnetic synergy and porous characteristics are two dominant factors in realizing light-weight and high-efficient microwave absorption performance.In this paper,a formaldehydeassisted metal-ligand crosslinking ...Electromagnetic synergy and porous characteristics are two dominant factors in realizing light-weight and high-efficient microwave absorption performance.In this paper,a formaldehydeassisted metal-ligand crosslinking strategy and a subsequent pyrolysis process are employed to synthesize magnetic porous carbon spheres with the electromagnetic synergy and porous characteristics,in which metal ions are tightly anchored in poly-(tannin acid)spheres because of the strong chelation coordination between them.The chemical composition of magnetic particles and the microwave absorption performance of the derived magnetic porous carbon spheres can be manipulated by adjusting the metal ions.Benefiting from the cooperative effects of porous structure,matched impedance,the electromagnetic synergistic enhancement between magnetic particles and carbon matrix,as well as the improved interfacial polarization caused by the large number of hetero-interfaces,both the microwave absorption intensity and the effective absorption bandwidths are significantly enhanced for magnetic porous carbon spheres,such as Co-PCSs and CoNi-PCSs,compared with PCSs.With 15 wt.%filler loading,the maximum reflection loss of CoNi-PCSs is -51 dB at 2.2 mm and the effective bandwidth is 7.2 GHz at 2.9 mm.Furthermore,this study provides the theoretical theory for the design and development of light-weight and highly efficient microwave absorption materials.展开更多
Incoherent optical processing of microwave signals,where low-coherence broadband light sources are employed instead of costly mode locked lasers,has attracted great interest thanks to its wide applications in microwav...Incoherent optical processing of microwave signals,where low-coherence broadband light sources are employed instead of costly mode locked lasers,has attracted great interest thanks to its wide applications in microwave photonics filtering[1–3],arbitrary generation[4–6]and analog to digital conversion[7]。展开更多
Rational design of hierarchical structures and a dual-interface built-in electric field(BIEF)are vital for enhancing dielectric loss and directional charge transport in microwave absorption materials(MAMs).Herein,we p...Rational design of hierarchical structures and a dual-interface built-in electric field(BIEF)are vital for enhancing dielectric loss and directional charge transport in microwave absorption materials(MAMs).Herein,we propose a dual-interface BIEF engineering strategy to construct a multifunctional MoS_(2)@C/CoS_(x)composites.Inspired by the spiderweb hunting mechanism,magnetic Co-based Prussian blue(PB)is electro spun with polyacrylonitrile to form Co@CoO/C nanofibers,followed by sulfidation to induce ordered array architectures.The structural evolution enables the formation of heterogeneous MoS_(2)-CoS_(x)-C interfaces and modulates the interfacial electric field intensity to enhance dielectric polarization.Density functional theory(DFT)calculations confirm that the work function difference(ΔΦ)of C/CoS_(2)/MoS_(2) is 6.179 eV,which indicates that the differencesΔΦamong MoS_(2),CoS_(x)and C components drive the spontaneous formation of dual-interface BIEF.This facilitates directional charge migration and strong dipolar/interface polarization,significantly improving the microwave attenuation capability.Benefiting from this design,the composite achieves a minimum reflection loss(RL_(min))of-63.83 dB and a maximum effective absorption bandwidth(EAB_(max))of 6.96 GHz,covering both C and Ku bands.In addition,the material reveals excellent infrared stealth performance due to its unique spiderweb-inspired ordered array structure.This study provides new insights into interfacial electric field modulation and a generalizable approach for designing multi-band and tunable microwave absorbers with synergistic electromagnetic and thermal stealth functions.展开更多
The Z-type barium ferrite/silica composites(Z-BCF/SiO2)were fabricated by in situ chemical synthesis method.The composition,structure,morphology and magnetic behavior of the composites were characterized by chemical a...The Z-type barium ferrite/silica composites(Z-BCF/SiO2)were fabricated by in situ chemical synthesis method.The composition,structure,morphology and magnetic behavior of the composites were characterized by chemical analysis,IR,XRD,SEM,TEM and VSM.The results indicated that there were some interactions between two components in the Z-BCF/SiO2 composites due to the coating of SiO2 on the Z-BCF particles.The magnetic properties of the Z-BCF/SiO2 composites were evidently less than that of the Z-BCF,owing to the small volume fraction of magnetic components in the samples.Due to the good transmission and loss properties on electromagnetic waves,the composites were better at microwave absorption than the parent component.Therefore,this research laid a foundation for the fabrication of highly efficient microwave absorbing material with enhanced wave impedance matching.展开更多
Over the past few years, the Utah Department of Transportation has developed the signal performance metrics （SPMs） system to evaluate the performance of signalized in- tersections dynamically. This system currently ...Over the past few years, the Utah Department of Transportation has developed the signal performance metrics （SPMs） system to evaluate the performance of signalized in- tersections dynamically. This system currently provides data summaries for several per- formance measures, one of them being turning movement counts collected by microwave sensors. As this system became public, there was a need to evaluate the accuracy of the data placed on the SPMs. A large-scale data collection was carried out to meet this need. Vehicles in the Hi-resolution data from microwave sensors were matched with the vehicles by ground-truth volume count data. Matching vehicles from the microwave sensor data and the ground-truth data manually collected required significant effort, A spreadsheet- based data analysis procedure was developed to carry out the task. A mixed model analysis of variance was used to analyze the effects of the factors considered on turning volume count accuracy. The analysis found that approach volume level and number of approach lanes would have significant effect on the accuracy of turning volume counts but the location of the sensors did not significantly affect the accuracy of turning volume counts. In addition, it was found that the location of lanes in relation to the sensor did not significantly affect the accuracy of lane-by-lane volume counts. This indicated that accu- racy analysis could be performed by using total approach volumes without comparing specific turning counts, that is, left-turn, through and right-turn movements. In general, the accuracy of approach volume counts collected by microwave sensors were within the margin of error that traffic engineers could accept. The procedure taken to perform the analysis and a summary of accuracy of volume counts for the factor combinations considered are presented in this paper.展开更多
基金Project(2023RC3066)supported by the Science and Technology Innovation Program of Hunan Province,ChinaProject(2023JJ50079)supported by the Hunan Provincial Natural Science Foundation,China。
文摘Carbonized melamine foam has been recognized as a promising material for microwave absorption due to its exceptional thermal stability,lightweight,and remarkable dielectric properties.In this study,we investigated the impact of nitric acid oxidation on the surface of carbonized melamine foam and its microwave absorption properties.The treated foam exhibits optimal reflection loss of−21.51 dB at 13.20 GHz,with an effective absorption bandwidth of 7.04 GHz.The enhanced absorption properties are primarily attributed to the strengthened dielectric loss,improved impedance matching,and increased polarization losses resulting from the oxidized surfaces.This research demonstrates a promising new approach for research into surface treatments to improve the performances of microwave absorbers.
基金financially supported by the National Natural Science Foundation of China(No.21403298)。
文摘In this study,flower-like MoS2 constructed by nanosheets was synthesized by a simple hydrothermal method.The hydrothermal process was optimized and the effects of hydrothermal condition,including reaction temperature,reaction time and the ratio of Mo source to S source(Mo:S)in precursor,on microwave absorption performances and dielectric properties were investigated.Our results showed that when the reaction temperature was 180℃,the reaction time was 18 h,and the Mo:S was 1:3.5,the synthesized MoS2 had the best performance:Its minimum reflection loss could reach-55.78 dB,and the corresponding matching thickness was 2.30 mm with a wide effective bandwidth of 5.17 GHz.Further researches on the microwave absorption mechanism revealed that in addition to the destructive interference of electromagnetic waves,various polarization phenomena such as defect dipole polarization were the main reasons for microwave loss.We believe that MoS2 is a candidate for a practical microwave absorbent.
基金This work was financially supported by the Shenyang Major Achievements Transformation Project(No.20-203-5-18).
文摘In this work,porous carbon particles were prepared from wheat flour by pyrolysis and activation.Through the subsequent coprecipitation and electroless plating,the surface and pores of carbon particles were modified by nickel-rich particles with different morphologies.Several loss mechanisms,including dielectric loss,magnetic loss,multiple reflection and scattering loss,were used to assess the attenuation ability to incident electromagnetic waves of these composite particles.The result shows that the chain-shaped morphology of nickel can provide the highest dielectric loss.Under the filler loading of 20 wt.%,the minimum reflection loss(RL min)reached-38.42 dB at 13.2 GHz,and the_(max)imum effective absorption bandwidth(EAB_(max))was 5.2 GHz with a matching thickness of 2 mm.The excellent performance of the composite particles is attributed to the synergistic effect of outstanding impedance matching and supe-rior electromagnetic loss ability caused by the chain structure.The result shows that the morphology of modifiers in carbon-based composites is important to improve microwave absorption performance,and this work provides inspiration for the design of high-performance porous carbon-based composites.
基金Project supported by the National Natural Science Foundation of China(Grant No.11074040)the Key Project of Department of Science and Technology of Shangdong Province of China(Grant No.ZR2012FZ006)
文摘The Co2FeSi films are deposited on Si （100） substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe-330 Oe （1 Oe = 79.5775 A.m ^-1）, and low coercivities in a range of 5 Oe-28 Oe. As a result, high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co2FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.
基金financially supported by the National Natural Science Foundation of China(No.52373271).
文摘Electromagnetic synergy and porous characteristics are two dominant factors in realizing light-weight and high-efficient microwave absorption performance.In this paper,a formaldehydeassisted metal-ligand crosslinking strategy and a subsequent pyrolysis process are employed to synthesize magnetic porous carbon spheres with the electromagnetic synergy and porous characteristics,in which metal ions are tightly anchored in poly-(tannin acid)spheres because of the strong chelation coordination between them.The chemical composition of magnetic particles and the microwave absorption performance of the derived magnetic porous carbon spheres can be manipulated by adjusting the metal ions.Benefiting from the cooperative effects of porous structure,matched impedance,the electromagnetic synergistic enhancement between magnetic particles and carbon matrix,as well as the improved interfacial polarization caused by the large number of hetero-interfaces,both the microwave absorption intensity and the effective absorption bandwidths are significantly enhanced for magnetic porous carbon spheres,such as Co-PCSs and CoNi-PCSs,compared with PCSs.With 15 wt.%filler loading,the maximum reflection loss of CoNi-PCSs is -51 dB at 2.2 mm and the effective bandwidth is 7.2 GHz at 2.9 mm.Furthermore,this study provides the theoretical theory for the design and development of light-weight and highly efficient microwave absorption materials.
文摘Incoherent optical processing of microwave signals,where low-coherence broadband light sources are employed instead of costly mode locked lasers,has attracted great interest thanks to its wide applications in microwave photonics filtering[1–3],arbitrary generation[4–6]and analog to digital conversion[7]。
基金supported by the National Natural Science Foundation of China(No.52462026)Postdoctoral Research Foundation of China(No.2018M643699)Shaanxi Province Postdoctoral Science Foundation(No.2018BSHEDZZ 101).
文摘Rational design of hierarchical structures and a dual-interface built-in electric field(BIEF)are vital for enhancing dielectric loss and directional charge transport in microwave absorption materials(MAMs).Herein,we propose a dual-interface BIEF engineering strategy to construct a multifunctional MoS_(2)@C/CoS_(x)composites.Inspired by the spiderweb hunting mechanism,magnetic Co-based Prussian blue(PB)is electro spun with polyacrylonitrile to form Co@CoO/C nanofibers,followed by sulfidation to induce ordered array architectures.The structural evolution enables the formation of heterogeneous MoS_(2)-CoS_(x)-C interfaces and modulates the interfacial electric field intensity to enhance dielectric polarization.Density functional theory(DFT)calculations confirm that the work function difference(ΔΦ)of C/CoS_(2)/MoS_(2) is 6.179 eV,which indicates that the differencesΔΦamong MoS_(2),CoS_(x)and C components drive the spontaneous formation of dual-interface BIEF.This facilitates directional charge migration and strong dipolar/interface polarization,significantly improving the microwave attenuation capability.Benefiting from this design,the composite achieves a minimum reflection loss(RL_(min))of-63.83 dB and a maximum effective absorption bandwidth(EAB_(max))of 6.96 GHz,covering both C and Ku bands.In addition,the material reveals excellent infrared stealth performance due to its unique spiderweb-inspired ordered array structure.This study provides new insights into interfacial electric field modulation and a generalizable approach for designing multi-band and tunable microwave absorbers with synergistic electromagnetic and thermal stealth functions.
基金supported by the National Natural Science Foundation of China(Grant No.21071125)the College Students’Science and Technology Innovation Activities Plan of Zhejiang(Grant No.2014R404056)Special and Key Laboratory of Functional Materials and Resource chemistry of Guizhou Provincial Education Department,Anshun University(Grant No.GAFMRC201304)
文摘The Z-type barium ferrite/silica composites(Z-BCF/SiO2)were fabricated by in situ chemical synthesis method.The composition,structure,morphology and magnetic behavior of the composites were characterized by chemical analysis,IR,XRD,SEM,TEM and VSM.The results indicated that there were some interactions between two components in the Z-BCF/SiO2 composites due to the coating of SiO2 on the Z-BCF particles.The magnetic properties of the Z-BCF/SiO2 composites were evidently less than that of the Z-BCF,owing to the small volume fraction of magnetic components in the samples.Due to the good transmission and loss properties on electromagnetic waves,the composites were better at microwave absorption than the parent component.Therefore,this research laid a foundation for the fabrication of highly efficient microwave absorbing material with enhanced wave impedance matching.
文摘Over the past few years, the Utah Department of Transportation has developed the signal performance metrics （SPMs） system to evaluate the performance of signalized in- tersections dynamically. This system currently provides data summaries for several per- formance measures, one of them being turning movement counts collected by microwave sensors. As this system became public, there was a need to evaluate the accuracy of the data placed on the SPMs. A large-scale data collection was carried out to meet this need. Vehicles in the Hi-resolution data from microwave sensors were matched with the vehicles by ground-truth volume count data. Matching vehicles from the microwave sensor data and the ground-truth data manually collected required significant effort, A spreadsheet- based data analysis procedure was developed to carry out the task. A mixed model analysis of variance was used to analyze the effects of the factors considered on turning volume count accuracy. The analysis found that approach volume level and number of approach lanes would have significant effect on the accuracy of turning volume counts but the location of the sensors did not significantly affect the accuracy of turning volume counts. In addition, it was found that the location of lanes in relation to the sensor did not significantly affect the accuracy of lane-by-lane volume counts. This indicated that accu- racy analysis could be performed by using total approach volumes without comparing specific turning counts, that is, left-turn, through and right-turn movements. In general, the accuracy of approach volume counts collected by microwave sensors were within the margin of error that traffic engineers could accept. The procedure taken to perform the analysis and a summary of accuracy of volume counts for the factor combinations considered are presented in this paper.
