A novel porous shock absorption layer is put forward in this study, and the shock absorption performance of the porous shock absorption layer is evaluated based on three-dimensional pseudo-static analysis. The modifie...A novel porous shock absorption layer is put forward in this study, and the shock absorption performance of the porous shock absorption layer is evaluated based on three-dimensional pseudo-static analysis. The modified reaction acceleration method is adopted and validated in the three-dimensional model. Seven ground motions are selected and the peak ground acceleration is adjusted to 0.2 g, 0.4 g and 0.6 g. The impact of the void ratio and thickness of the porous shock absorption layer is studied, while the surrounding rock grade and tunnel depth are also investigated. The numerical results show that the porous shock absorption layer has good shock absorption performance and can effectively reduce the maximum internal force of the secondary lining, but it cannot reduce the maximum horizontal relative displacement of the secondary lining. The circumferential rubber strip in the porous shock absorption layer will reduce shock absorption performance. The results of parameter analysis indicate that the shock absorption performance of the porous shock absorption layer increases with the increase of the void ratio and thickness, and it has good shock absorption performance under different surrounding rock grades and tunnel depths.展开更多
Re-entrant honeycombs are widely used in safeguard structures due to their geometric simplicity and excellent energy absorption capacities.However,traditional re-entrant honeycombs exhibit insufficient stiffness and s...Re-entrant honeycombs are widely used in safeguard structures due to their geometric simplicity and excellent energy absorption capacities.However,traditional re-entrant honeycombs exhibit insufficient stiffness and stability owing to the lack of internal support.This paper proposes a new hybrid honeycomb by integrating a chiral component inside the re-entrant honeycomb.Since Young's modulus is a key parameter to evaluate the energy absorption performance and stiffness,an analytical model is given to predict the effective Young's modulus of the proposed hybrid honeycomb.It is found that the optimal design scheme is to directly insert a circular ring inside the re-entrant honeycomb.The normalized specific energy absorption(SEA)of the hybrid honeycomb is 95%larger than that of the traditional re-entrant honeycomb.The normalized SEA first increases to a peak value and then decreases with the cell wall thickness.The optimal thickness of the cell wall for the maximum SEA is derived in terms of the geometric configuration of the unit cell.The normalized SEA first decreases to a valley value and then increases with the re-entrant angle.A longer horizontal cell wall results in a smaller normalized SEA.This paper provides a new design method for safeguard structures with high stiffness and energy absorption performance.展开更多
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
The rapid development of additive manufacturing technology has offered a new avenue for designing and fabricating high wave-absorbing meta structures.In this study,the mechanical properties and broadband absorption pe...The rapid development of additive manufacturing technology has offered a new avenue for designing and fabricating high wave-absorbing meta structures.In this study,the mechanical properties and broadband absorption performance of Poly-Ether-Ether-Ketone(PEEK)–based electromagnetic wave–absorbing composite materials was investigated.The high-performance polymer PEEK was used as the matrix,and the materials with electromagnetic wave loss,such as reduced graphene oxide,Carbonyl Iron(CI),and Flake CI(FCI),were used as absorbers.Based on the theory of impedance matching,a wave-absorbing structure with a gradual impedance gradient was designed and printed.The test results showed that at the 2.0–18.0 GHz frequency band,the coverage rate of the effective absorption bandwidth was up to 72.0%,the average optimal reflectivity was–18.09 dB,and the wide-angle absorption range was 0°–30°.The advantages of additive manufacturing technology in designing and fabricating wave-absorbing structures are presented,demonstrating that the technology is an effective method for creating broadband absorbing structures.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
Whereas hollow composites present some superiorities like abundant micro interfaces,outstanding impedance matching as the responses of electromagnetic wave(EMW),but versatile designs including crystal transformation,h...Whereas hollow composites present some superiorities like abundant micro interfaces,outstanding impedance matching as the responses of electromagnetic wave(EMW),but versatile designs including crystal transformation,heterogeneous structures and magnetic exchange coupling to further contribution are even not designed or stressed together in previous literatures.In this article,rational design on the hollow CoFe_(2)O_(4)/CoFe@C architecture has been conducted by a sequential process of self-sacrifice by combustion,in-suit polymerization and calcination.Results of morphology observation exhibit that heterogeneous CoFe_(2)O_(4)/CoFe@C composites were generated via crystal transformation from CoFe_(2)O_(4) to CoFe alloys with encapsulated carbon,together with ultimate growth of crystal particles.As for three carbon-based architectures,relatively low-graphitization carbon layers are favorable for enhancing impedance matching and polarization relaxation,but suppressing the conductive loss essentially.Moderate carbon content endows sample S2 with the maximum magnetic saturation(Ms)of 152.4 emu g^(-1).The optimized RL of sample S3 is up to-51 dB with 30 wt%loading,and the effective absorption band(EAB)is of 5.9 GHz at the thickness of 2.17 mm,while 6.0 GHz can be reached at 2.5 mm.Therefore,this hollow multi-interfaces design definitely shed light on novel structure for new excellent absorbers.展开更多
In order to improve the dust absorption performance of the reverse blowing pickup mouth, the gas-solid flow motion properties inside the reverse blowing pickup mouth were simulated by using computational fluid dynamic...In order to improve the dust absorption performance of the reverse blowing pickup mouth, the gas-solid flow motion properties inside the reverse blowing pickup mouth were simulated by using computational fluid dynamics( CFD) software,Fluent.The results show that both the front baffle inclination angle and the pressure drop across the pickup mouth have significant impacts on dust absorption performance. As the inclination angle is increased,there is an increase in the overall and grade removal efficiency. As the front baffle inclination angle or pressure drop is increased,there is an increase in the overall and grade removal efficiencies.However,pressure drop affects energy consumption. Front baffle inclination angle and pressure drop are optimized. Optimal inclination angle and pressure drop are 105° and 2 300 Pa respectively. Sample machine is made and measured,which further verifies the appropriateness of numerical simulation and practicability of optimum strategy.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
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
SiOC-based ceramics are considered promising electromagnetic wave-absorbing materials because of their lightweight,high-temperature resistance,and heat insulation properties.Herein,SiOC@C ceramic nanospheres were prep...SiOC-based ceramics are considered promising electromagnetic wave-absorbing materials because of their lightweight,high-temperature resistance,and heat insulation properties.Herein,SiOC@C ceramic nanospheres were prepared using a liquid-phase method combined with a polymer-derived ceramic(PDC)method,followed by heat treatment in N_(2) and Ar atmospheres at different temperatures.The morphology,microstructure,phase composition,and electromagnetic wave absorption performance of the SiOC@C ceramic nanospheres were investigated in detail.The SiOC@C ceramic nanospheres obtained in the Ar atmosphere showed a minimum reflection loss(RL_(min))of−67.03 dB,whereas the SiOC@C ceramic nanospheres obtained in the N_(2) atmosphere exhibited an RLmin value of−63.76 dB.The outstanding electromagnetic wave absorption performance of the SiOC@C ceramic nanospheres was attributed to the synergistic effect between conductive loss,interfacial/defect polarization loss,multiple reflections,and scattering.Therefore,this research provides valuable insights into the design and fabrication of SiOC ceramic-based electromagnetic wave absorbers.展开更多
Currently,the microwave absorbers usually suffer dreadful electromagnetic wave absorption(EMWA)performance damping at elevated temperature due to impedance mismatching induced by increased conduction loss.Consequently...Currently,the microwave absorbers usually suffer dreadful electromagnetic wave absorption(EMWA)performance damping at elevated temperature due to impedance mismatching induced by increased conduction loss.Consequently,the development of high-performance EMWA materials with good impedance matching and strong loss ability in wide temperature spectrum has emerged as a top priority.Herein,due to the high melting point,good electrical conductivity,excellent environmental stability,EM coupling effect,and abundant interfaces of titanium nitride(TiN)nanotubes,they were designed based on the controlling kinetic diffusion procedure and Ostwald ripening process.Benefiting from boosted heterogeneous interfaces between TiN nanotubes and polydimethylsiloxane(PDMS),enhanced polarization loss relaxations were created,which could not only improve the depletion efficiency of EMWA,but also contribute to the optimized impedance matching at elevated temperature.Therefore,the TiN nanotubes/PDMS composite showed excellent EMWA performances at varied temperature(298-573 K),while achieved an effective absorption bandwidth(EAB)value of 3.23 GHz and a minimum reflection loss(RLmin)value of−44.15 dB at 423 K.This study not only clarifies the relationship between dielectric loss capacity(conduction loss and polarization loss)and temperature,but also breaks new ground for EM absorbers in wide temperature spectrum based on interface engineering.展开更多
Electromagnetic absorption(EMA)materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles.However,meeting these two requirements is ...Electromagnetic absorption(EMA)materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles.However,meeting these two requirements is always a great challenge,which excluded the most attractive lightweight candidates,such as carbon-based materials.In this study,SiC_(nw)-reinfbrced SiCNO(SiC_(nw)/SiCNO)composite aerogels were fabricated through the in-situ growth of SiC_(nw) in polymer-derived SiCNO ceramic aerogels by using catalyst-assisted microwave heating at ultra-low temperature and in short time.The phase composition,microstructure,and EMA property of the SiC_(nw)/SiCNO composite aerogels were systematically investigated.The results indicated that the morphology and phase composition of SiC_(nw)/SiCNO composite aerogels can be regulated easily by varying the microwave treatment temperature.The composite aerogels show excellent EMA property with minimum reflection loss of -23.9 dB@13.8 GHz,-26.5 dB@10.9 GHz,and -20.4 dB@14.5 GHz and the corresponding effective bandwidth of 5.2 GHz,3.2 GHz,and 4.8 GHz at 2.0 mm thickness for microwave treatment at 600℃,800℃,and 1000℃,respectively,which is much better than that of SiCN ceramic aerogels.The superior EMA performance is mainly attributed to the improved impedance matching,multireflection,multi-interfacial polarization,and micro current caused by migration of hopping electrons.展开更多
The electric vertical takeoff and landing(e VTOL)aircraft shows great potential for rapid military personnel deployment on the battlefield.However,its susceptibility to control loss,complex crashes,and extremely limit...The electric vertical takeoff and landing(e VTOL)aircraft shows great potential for rapid military personnel deployment on the battlefield.However,its susceptibility to control loss,complex crashes,and extremely limited bottom energy-absorbing space demands higher comprehensive crashworthiness of its subfloor thin-walled structures.This study investigated the energy absorption capacity of novel concave polygonal carbon fiber reinforced plastics(CFRP)tubes under multi-angle collisions.Quasistatic compression experiments and finite element simulations were conducted to assess the failure mode and energy absorption.The influences of cross-section shapes,loading conditions,and geometry parameters on crashworthiness metrics were further analyzed.The results revealed that,under the similar weight,concave polygonal tubes exhibited superior energy absorption under axial loads compared to regular polygonal and circular tubes,attributed to the increased number of axial splits.However,both regular and concave polygonal tubes,particularly the latter,demonstrated reduced oblique energy absorption compared to traditional square tubes with the increasing ratio of SEA value decreased from 20%-16%.Notably,this reduction in energy absorption can be compensated for by the implementation of inward and outward crusher plugs,and with them,the concave polygonal tubes demonstrated outstanding overall crashworthiness performance under multiple loading conditions.This concave cross-sectional design methods could serve as a guidance for the development of the eVTOL subfloor.展开更多
The development of multifunctional composites with desirable electromagnetic wave absorption and antibacterial performance for the medical field has aroused wide interest.In this work,SioC/Ag composites were successfu...The development of multifunctional composites with desirable electromagnetic wave absorption and antibacterial performance for the medical field has aroused wide interest.In this work,SioC/Ag composites were successfully fabricated via the liquid-phase method.When the filler content of SiOC/Ag-3 is 40wt%,SiOC/Ag-3exhibits excellent electromagnetic wave absorption performance,achieving a minimum reflection loss(RL_(min))value of-58.03 dB with a matching thickness of only 2.82 mm.The superior electromagnetic wave absorption performance is attributed to(i)multiple reflections,(ii)conductive loss,and(iii)interfacial polarization loss.In addition,the radar cross-section(RCS)simulation indicates that all RCS values of the perfect electric conductor(PEC)with the SioC/Ag-3 coating are below-20 dB-m^(2)across the incident angle range from-60°to 60,indicating strong radar stealth performance.Moreover,SiOC/Ag composites also achieve excellent antibacterial ability against E.coli and S.aureus through the generation of reactive oxygen species(ROS)under visible light irradiation.This work provides new insights into the design and development of bifunctional composites with electromagnetic wave absorption and antibacterial performancefor application in medical devices.展开更多
Mechanical properties and low cycle fatigue are two factors that must be considered in developin gnew type steel for shock absorption. Process capability and process control are significant factors in achieving the pu...Mechanical properties and low cycle fatigue are two factors that must be considered in developin gnew type steel for shock absorption. Process capability and process control are significant factors in achieving the purpose of research and development programs. Often-used evaluation methods failed to measure processyield and process centering ; so this paper uses Taguchi loss function as basis to establish an evaluation methodand the steps for assessing the quality of mechanical properties and process control of an iron and steel manu-facturer. The establishment of this method can serve the research and development and manufacturing industry and lay a foundation in enhancing its process control ability to select better manufacturing processes that are more reliable than decision making by using the other commonly used methods.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)-CoSx-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
Electromagnetic(EM)absorption is paving the way to overcome the challenges related to conventional shielding strategy against EM pollution through sustainable energy dissipation.As characteristic functional media that...Electromagnetic(EM)absorption is paving the way to overcome the challenges related to conventional shielding strategy against EM pollution through sustainable energy dissipation.As characteristic functional media that can interact with electric or magnetic field branch,EM wave absorption materials(EWAMs)have received extensive attention and realized considerable development in the past two decades,where carbon-based composites are always considered as promising candidates for high-performance EMAWs due to their synergetic loss mechanism as well as diversified composition and microstructure design.Recent progress indicates that there is more and more interest in the fabrication of carbon-based composites with unique core–shell configuration.On one hand,core–shell configuration usually ensures good chemical homogeneity of final products and provides some positive protections for the components with susceptibility to corrosion,on the other hand,it creates enough heterogeneous interfaces between different EM components,which may bring enhanced polarization effect and intensify the consumption of EM energy.In this review,we firstly introduce EM wave absorption theory,and then highlight the advances of core–shell engineering in carbonbased composites in terms of built-in carbon cores and built-out carbon shells.Moreover,we also show some special core–shell carbon-based composites,including carbon/carbon composites,assembled composites,and decorated composites.After analyzing EM absorption performance of some representative composites,we further propose some challenges and perspectives on the development of core–shell carbon-based composites.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
To solve the severe electromagnetic(EM)radiation from the widespread application of electronic equipment,we developed a simple template-guided oxypolymerization strategy to synthesize polypyrrole(PPy)planar helixes as...To solve the severe electromagnetic(EM)radiation from the widespread application of electronic equipment,we developed a simple template-guided oxypolymerization strategy to synthesize polypyrrole(PPy)planar helixes as an efficient EM wave(EMW)absorber,and systematically investigated the morphology-dependent chirality,conductivity,and microwave absorption properties.As HCl concentration[HCl]varied from 0 to 2.0 M,the morphology evolved from planar helix to 3D cross-linking network structures,the conductivity increased from 0.0019 to 0.0302 S/cm,and the EM parameters peaked at[HCl]=0.5 M.Compared to other absorbers,the PPy planar helix formed at[HCl]=0 M possessed wider absorption band(5.84 GHz),smaller matching thickness(1.6 mm),lower loading(25 wt.%),and intenser absorption(-48.17 dB).The reason lies in the strong attenuation capability,multiple resonances,multiple scattering,and good impedance matching generated by chiral PPy planar helixes with a distinctive helical configuration,doped heteroatoms(O,S),and a local conductive network.Our results suggest that PPy planar helixes offer great promise for fields such as chiral sensors,electronics,optics,chiral catalysis,and EMW absorption and shielding due to their distinctive morphology,tunable conductivity,and outstanding EMW absorption properties(EMWAPs).展开更多
基金Science and Technology Plan Project of Xizang Autonomous Region,China under Grant No.XZ202501YD0007。
文摘A novel porous shock absorption layer is put forward in this study, and the shock absorption performance of the porous shock absorption layer is evaluated based on three-dimensional pseudo-static analysis. The modified reaction acceleration method is adopted and validated in the three-dimensional model. Seven ground motions are selected and the peak ground acceleration is adjusted to 0.2 g, 0.4 g and 0.6 g. The impact of the void ratio and thickness of the porous shock absorption layer is studied, while the surrounding rock grade and tunnel depth are also investigated. The numerical results show that the porous shock absorption layer has good shock absorption performance and can effectively reduce the maximum internal force of the secondary lining, but it cannot reduce the maximum horizontal relative displacement of the secondary lining. The circumferential rubber strip in the porous shock absorption layer will reduce shock absorption performance. The results of parameter analysis indicate that the shock absorption performance of the porous shock absorption layer increases with the increase of the void ratio and thickness, and it has good shock absorption performance under different surrounding rock grades and tunnel depths.
基金Project supported by Guangdong Basic and Applied Basic Research Foundation(Nos.2022A1515240072,2023A1515240053,2022B1515020099,and 2023A1515012641)Shenzhen Science and Technology Program(No.JCYJ20220818102409020)the National Natural Science Foundation of China(Nos.12102104 and 12002180)。
文摘Re-entrant honeycombs are widely used in safeguard structures due to their geometric simplicity and excellent energy absorption capacities.However,traditional re-entrant honeycombs exhibit insufficient stiffness and stability owing to the lack of internal support.This paper proposes a new hybrid honeycomb by integrating a chiral component inside the re-entrant honeycomb.Since Young's modulus is a key parameter to evaluate the energy absorption performance and stiffness,an analytical model is given to predict the effective Young's modulus of the proposed hybrid honeycomb.It is found that the optimal design scheme is to directly insert a circular ring inside the re-entrant honeycomb.The normalized specific energy absorption(SEA)of the hybrid honeycomb is 95%larger than that of the traditional re-entrant honeycomb.The normalized SEA first increases to a peak value and then decreases with the cell wall thickness.The optimal thickness of the cell wall for the maximum SEA is derived in terms of the geometric configuration of the unit cell.The normalized SEA first decreases to a valley value and then increases with the re-entrant angle.A longer horizontal cell wall results in a smaller normalized SEA.This paper provides a new design method for safeguard structures with high stiffness and energy absorption performance.
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the National Natural Science Foundation of China(No.12272298).
文摘The rapid development of additive manufacturing technology has offered a new avenue for designing and fabricating high wave-absorbing meta structures.In this study,the mechanical properties and broadband absorption performance of Poly-Ether-Ether-Ketone(PEEK)–based electromagnetic wave–absorbing composite materials was investigated.The high-performance polymer PEEK was used as the matrix,and the materials with electromagnetic wave loss,such as reduced graphene oxide,Carbonyl Iron(CI),and Flake CI(FCI),were used as absorbers.Based on the theory of impedance matching,a wave-absorbing structure with a gradual impedance gradient was designed and printed.The test results showed that at the 2.0–18.0 GHz frequency band,the coverage rate of the effective absorption bandwidth was up to 72.0%,the average optimal reflectivity was–18.09 dB,and the wide-angle absorption range was 0°–30°.The advantages of additive manufacturing technology in designing and fabricating wave-absorbing structures are presented,demonstrating that the technology is an effective method for creating broadband absorbing structures.
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 supported by the National Natural Science Foundation of China(No.51622106)the Liao Ning Revitalization Talents Program(No.XLYC1807076)。
文摘Whereas hollow composites present some superiorities like abundant micro interfaces,outstanding impedance matching as the responses of electromagnetic wave(EMW),but versatile designs including crystal transformation,heterogeneous structures and magnetic exchange coupling to further contribution are even not designed or stressed together in previous literatures.In this article,rational design on the hollow CoFe_(2)O_(4)/CoFe@C architecture has been conducted by a sequential process of self-sacrifice by combustion,in-suit polymerization and calcination.Results of morphology observation exhibit that heterogeneous CoFe_(2)O_(4)/CoFe@C composites were generated via crystal transformation from CoFe_(2)O_(4) to CoFe alloys with encapsulated carbon,together with ultimate growth of crystal particles.As for three carbon-based architectures,relatively low-graphitization carbon layers are favorable for enhancing impedance matching and polarization relaxation,but suppressing the conductive loss essentially.Moderate carbon content endows sample S2 with the maximum magnetic saturation(Ms)of 152.4 emu g^(-1).The optimized RL of sample S3 is up to-51 dB with 30 wt%loading,and the effective absorption band(EAB)is of 5.9 GHz at the thickness of 2.17 mm,while 6.0 GHz can be reached at 2.5 mm.Therefore,this hollow multi-interfaces design definitely shed light on novel structure for new excellent absorbers.
基金National Natural Science Foundation of China(No.51375202)
文摘In order to improve the dust absorption performance of the reverse blowing pickup mouth, the gas-solid flow motion properties inside the reverse blowing pickup mouth were simulated by using computational fluid dynamics( CFD) software,Fluent.The results show that both the front baffle inclination angle and the pressure drop across the pickup mouth have significant impacts on dust absorption performance. As the inclination angle is increased,there is an increase in the overall and grade removal efficiency. As the front baffle inclination angle or pressure drop is increased,there is an increase in the overall and grade removal efficiencies.However,pressure drop affects energy consumption. Front baffle inclination angle and pressure drop are optimized. Optimal inclination angle and pressure drop are 105° and 2 300 Pa respectively. Sample machine is made and measured,which further verifies the appropriateness of numerical simulation and practicability of optimum strategy.
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.
基金supported by the National Natural Science Foundation of China(No.52360018)the Shiyanjia Lab(www.shiyanjia.com)for the support of thermogravimetric(TG)tests.
文摘SiOC-based ceramics are considered promising electromagnetic wave-absorbing materials because of their lightweight,high-temperature resistance,and heat insulation properties.Herein,SiOC@C ceramic nanospheres were prepared using a liquid-phase method combined with a polymer-derived ceramic(PDC)method,followed by heat treatment in N_(2) and Ar atmospheres at different temperatures.The morphology,microstructure,phase composition,and electromagnetic wave absorption performance of the SiOC@C ceramic nanospheres were investigated in detail.The SiOC@C ceramic nanospheres obtained in the Ar atmosphere showed a minimum reflection loss(RL_(min))of−67.03 dB,whereas the SiOC@C ceramic nanospheres obtained in the N_(2) atmosphere exhibited an RLmin value of−63.76 dB.The outstanding electromagnetic wave absorption performance of the SiOC@C ceramic nanospheres was attributed to the synergistic effect between conductive loss,interfacial/defect polarization loss,multiple reflections,and scattering.Therefore,this research provides valuable insights into the design and fabrication of SiOC ceramic-based electromagnetic wave absorbers.
基金the National Nature Science Foundation of China(No.22305066).
文摘Currently,the microwave absorbers usually suffer dreadful electromagnetic wave absorption(EMWA)performance damping at elevated temperature due to impedance mismatching induced by increased conduction loss.Consequently,the development of high-performance EMWA materials with good impedance matching and strong loss ability in wide temperature spectrum has emerged as a top priority.Herein,due to the high melting point,good electrical conductivity,excellent environmental stability,EM coupling effect,and abundant interfaces of titanium nitride(TiN)nanotubes,they were designed based on the controlling kinetic diffusion procedure and Ostwald ripening process.Benefiting from boosted heterogeneous interfaces between TiN nanotubes and polydimethylsiloxane(PDMS),enhanced polarization loss relaxations were created,which could not only improve the depletion efficiency of EMWA,but also contribute to the optimized impedance matching at elevated temperature.Therefore,the TiN nanotubes/PDMS composite showed excellent EMWA performances at varied temperature(298-573 K),while achieved an effective absorption bandwidth(EAB)value of 3.23 GHz and a minimum reflection loss(RLmin)value of−44.15 dB at 423 K.This study not only clarifies the relationship between dielectric loss capacity(conduction loss and polarization loss)and temperature,but also breaks new ground for EM absorbers in wide temperature spectrum based on interface engineering.
基金the financial support from the National Natural Science Foundation of China(Nos.U1904180 and 52072344)Excellent Young Scientists Fund of Henan Province(No.202300410369)+1 种基金Henan Province University Innovation Talents Support Program(No.21HASTIT001)China Postdoctoral Science Foundation(No.2021M692897).
文摘Electromagnetic absorption(EMA)materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles.However,meeting these two requirements is always a great challenge,which excluded the most attractive lightweight candidates,such as carbon-based materials.In this study,SiC_(nw)-reinfbrced SiCNO(SiC_(nw)/SiCNO)composite aerogels were fabricated through the in-situ growth of SiC_(nw) in polymer-derived SiCNO ceramic aerogels by using catalyst-assisted microwave heating at ultra-low temperature and in short time.The phase composition,microstructure,and EMA property of the SiC_(nw)/SiCNO composite aerogels were systematically investigated.The results indicated that the morphology and phase composition of SiC_(nw)/SiCNO composite aerogels can be regulated easily by varying the microwave treatment temperature.The composite aerogels show excellent EMA property with minimum reflection loss of -23.9 dB@13.8 GHz,-26.5 dB@10.9 GHz,and -20.4 dB@14.5 GHz and the corresponding effective bandwidth of 5.2 GHz,3.2 GHz,and 4.8 GHz at 2.0 mm thickness for microwave treatment at 600℃,800℃,and 1000℃,respectively,which is much better than that of SiCN ceramic aerogels.The superior EMA performance is mainly attributed to the improved impedance matching,multireflection,multi-interfacial polarization,and micro current caused by migration of hopping electrons.
基金financially supported by the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.24qnpy041)the Science and Technology Innovation Key R&D Program of Chongqing(Grant No.CSTB2023TIAD-STX0030)。
文摘The electric vertical takeoff and landing(e VTOL)aircraft shows great potential for rapid military personnel deployment on the battlefield.However,its susceptibility to control loss,complex crashes,and extremely limited bottom energy-absorbing space demands higher comprehensive crashworthiness of its subfloor thin-walled structures.This study investigated the energy absorption capacity of novel concave polygonal carbon fiber reinforced plastics(CFRP)tubes under multi-angle collisions.Quasistatic compression experiments and finite element simulations were conducted to assess the failure mode and energy absorption.The influences of cross-section shapes,loading conditions,and geometry parameters on crashworthiness metrics were further analyzed.The results revealed that,under the similar weight,concave polygonal tubes exhibited superior energy absorption under axial loads compared to regular polygonal and circular tubes,attributed to the increased number of axial splits.However,both regular and concave polygonal tubes,particularly the latter,demonstrated reduced oblique energy absorption compared to traditional square tubes with the increasing ratio of SEA value decreased from 20%-16%.Notably,this reduction in energy absorption can be compensated for by the implementation of inward and outward crusher plugs,and with them,the concave polygonal tubes demonstrated outstanding overall crashworthiness performance under multiple loading conditions.This concave cross-sectional design methods could serve as a guidance for the development of the eVTOL subfloor.
基金supported by the Science Foundation of Jiangxi Provincial Department of Education(No.GJ2400915)the Early Career Youth Science and Technology Talent Training Project of Jiangxi Province(No.20244BCE52206)the National Natural Science Foundation of China(No.52360018).
文摘The development of multifunctional composites with desirable electromagnetic wave absorption and antibacterial performance for the medical field has aroused wide interest.In this work,SioC/Ag composites were successfully fabricated via the liquid-phase method.When the filler content of SiOC/Ag-3 is 40wt%,SiOC/Ag-3exhibits excellent electromagnetic wave absorption performance,achieving a minimum reflection loss(RL_(min))value of-58.03 dB with a matching thickness of only 2.82 mm.The superior electromagnetic wave absorption performance is attributed to(i)multiple reflections,(ii)conductive loss,and(iii)interfacial polarization loss.In addition,the radar cross-section(RCS)simulation indicates that all RCS values of the perfect electric conductor(PEC)with the SioC/Ag-3 coating are below-20 dB-m^(2)across the incident angle range from-60°to 60,indicating strong radar stealth performance.Moreover,SiOC/Ag composites also achieve excellent antibacterial ability against E.coli and S.aureus through the generation of reactive oxygen species(ROS)under visible light irradiation.This work provides new insights into the design and development of bifunctional composites with electromagnetic wave absorption and antibacterial performancefor application in medical devices.
文摘Mechanical properties and low cycle fatigue are two factors that must be considered in developin gnew type steel for shock absorption. Process capability and process control are significant factors in achieving the purpose of research and development programs. Often-used evaluation methods failed to measure processyield and process centering ; so this paper uses Taguchi loss function as basis to establish an evaluation methodand the steps for assessing the quality of mechanical properties and process control of an iron and steel manu-facturer. The establishment of this method can serve the research and development and manufacturing industry and lay a foundation in enhancing its process control ability to select better manufacturing processes that are more reliable than decision making by using the other commonly used methods.
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)-CoSx-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(No.21676065).
文摘Electromagnetic(EM)absorption is paving the way to overcome the challenges related to conventional shielding strategy against EM pollution through sustainable energy dissipation.As characteristic functional media that can interact with electric or magnetic field branch,EM wave absorption materials(EWAMs)have received extensive attention and realized considerable development in the past two decades,where carbon-based composites are always considered as promising candidates for high-performance EMAWs due to their synergetic loss mechanism as well as diversified composition and microstructure design.Recent progress indicates that there is more and more interest in the fabrication of carbon-based composites with unique core–shell configuration.On one hand,core–shell configuration usually ensures good chemical homogeneity of final products and provides some positive protections for the components with susceptibility to corrosion,on the other hand,it creates enough heterogeneous interfaces between different EM components,which may bring enhanced polarization effect and intensify the consumption of EM energy.In this review,we firstly introduce EM wave absorption theory,and then highlight the advances of core–shell engineering in carbonbased composites in terms of built-in carbon cores and built-out carbon shells.Moreover,we also show some special core–shell carbon-based composites,including carbon/carbon composites,assembled composites,and decorated composites.After analyzing EM absorption performance of some representative composites,we further propose some challenges and perspectives on the development of core–shell carbon-based composites.
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.
基金supported by the National Natural Science Foundation of China(Grant No. 52073260)the Public Utility Items of Zhejiang Province (Grant No. LGG21E020002)+1 种基金the Industrial Key Projects of Jinhua City (Grant No.2019A12238)the Self-Topic Fund of Zhejiang Normal University(Grant No. 2020ZS04)
文摘To solve the severe electromagnetic(EM)radiation from the widespread application of electronic equipment,we developed a simple template-guided oxypolymerization strategy to synthesize polypyrrole(PPy)planar helixes as an efficient EM wave(EMW)absorber,and systematically investigated the morphology-dependent chirality,conductivity,and microwave absorption properties.As HCl concentration[HCl]varied from 0 to 2.0 M,the morphology evolved from planar helix to 3D cross-linking network structures,the conductivity increased from 0.0019 to 0.0302 S/cm,and the EM parameters peaked at[HCl]=0.5 M.Compared to other absorbers,the PPy planar helix formed at[HCl]=0 M possessed wider absorption band(5.84 GHz),smaller matching thickness(1.6 mm),lower loading(25 wt.%),and intenser absorption(-48.17 dB).The reason lies in the strong attenuation capability,multiple resonances,multiple scattering,and good impedance matching generated by chiral PPy planar helixes with a distinctive helical configuration,doped heteroatoms(O,S),and a local conductive network.Our results suggest that PPy planar helixes offer great promise for fields such as chiral sensors,electronics,optics,chiral catalysis,and EMW absorption and shielding due to their distinctive morphology,tunable conductivity,and outstanding EMW absorption properties(EMWAPs).
