In order to ensure the operational reliability and infor-mation security of sophisticated electronic components and to protect human health,efficient electromagnetic interference(EMI)shielding materials are required t...In order to ensure the operational reliability and infor-mation security of sophisticated electronic components and to protect human health,efficient electromagnetic interference(EMI)shielding materials are required to attenuate electromagnetic wave energy.In this work,the cellulose solution is obtained by dissolving cotton through hydrogen bond driving self-assembly using sodium hydroxide(NaOH)/urea solution,and cellulose aerogels(CA)are prepared by gelation and freeze-drying.Then,the cellulose carbon aerogel@reduced graphene oxide aerogels(CCA@rGO)are prepared by vacuum impregnation,freeze-drying followed by thermal annealing,and finally,the CCA@rGO/polydimethylsiloxane(PDMS)EMI shielding composites are prepared by backfilling with PDMS.Owing to skin-core structure of CCA@rGO,the complete three-dimensional(3D)double-layer con-ductive network can be successfully constructed.When the loading of CCA@rGO is 3.05 wt%,CCA@rGO/PDMS EMI shielding composites have an excellent EMI shielding effectiveness(EMI SE)of 51 dB,which is 3.9 times higher than that of the co-blended CCA/rGO/PDMS EMI shielding composites(13 dB)with the same loading of fillers.At this time,the CCA@rGO/PDMS EMI shielding composites have excellent thermal stability(T_(HRI) of 178.3℃)and good thermal conductivity coefficient(λ of 0.65 W m^(-1) K^(-1)).Excellent comprehensive performance makes CCA@rGO/PDMS EMI shielding composites great prospect for applications in lightweight,flexible EMI shielding composites.展开更多
在中高压大容量的工作环境下,有源电力滤波器(active power filter,APF)谐波抑制性能及产生的电磁干扰受到主电路功率半导体器件开关频率的制约。提出一种适用于中高压混合型并联有源电力滤波器的新型滑模控制方法。该方法对电网电流和...在中高压大容量的工作环境下,有源电力滤波器(active power filter,APF)谐波抑制性能及产生的电磁干扰受到主电路功率半导体器件开关频率的制约。提出一种适用于中高压混合型并联有源电力滤波器的新型滑模控制方法。该方法对电网电流和APF直流母线中点电位进行解耦跟踪控制,并将对状态变量的跟踪控制和脉宽调制(pulse width modulation,PWM)统一起来,在相同的谐波抑制精度下,可实现对开关频率的优化,将其约束在较低的确定频带内。仿真和实验结果证明,该滑模控制方法可以有效抑制由电网电压畸变和非线性负载引起的谐波电流,同时具有电磁干扰小的优点。展开更多
With the widespread application of electronic communication technology,the resulting electromagnetic radiation pollution has been significantly increased.Metal matrix electromagnetic interference(EMI)shielding materia...With the widespread application of electronic communication technology,the resulting electromagnetic radiation pollution has been significantly increased.Metal matrix electromagnetic interference(EMI)shielding materials have disadvantages such as high density,easy corrosion,difficult processing and high price,etc.Polymer matrix EMI shielding composites possess light weight,corrosion resistance and easy processing.However,the current polymer matrix composites present relatively low electrical conductivity and poor EMI shielding performance.This review firstly discusses the key concept,loss mechanism and test method of EMI shielding.Then the current development status of EMI shielding materials is summarized,and the research progress of polymer matrix EMI shielding composites with different structures is illustrated,especially for their preparation methods and evaluation.Finally,the corresponding key scientific and technical problems are proposed,and their development trend is also prospected.展开更多
Renewable porous biochar and 2 D MXene have attracted significant attention in high-end electromagnetic interference(EMI)shielding fields,due to unique orderly structures and excellent electrical conductivity(r)value....Renewable porous biochar and 2 D MXene have attracted significant attention in high-end electromagnetic interference(EMI)shielding fields,due to unique orderly structures and excellent electrical conductivity(r)value.In this work,the wood-derived porous carbon(WPC)skeleton from natural wood was performed as a template.And excellent conductive and ultra-light 3D MXene aerogel was then constructed to prepare the MXene aerogel/WPC composites,based on highly ordered honeycomb cells inner WPC as a microreactor.Higher carbonization temperature is more conducive to the graphitization degree of natural wood.MXene aerogel/WPC composites achieve the optimal EMI SE value of up to 71.3 d B at density as low as 0.197 g/cm^3.Such wall-like"mortar-brick"structures(WPC skeleton as"mortar"and MXene aerogel as"brick")not only effectively solve the unstable structure problem of MXene aerogel networks,but also greatly prolong the transmission paths of the electromagnetic waves and dissipate the incident electromagnetic waves in the form of heat and electric energy,thereby exhibiting the superior EMI shielding performance.In addition,MXene aerogel/WPC composites also exhibit good anisotropic compressive strength,excellent thermal insulation and flame retardant properties.Such ultra-light,green and efficient multi-functional bio-carbon-based composites have great application potential in the high-end EMI shielding fields of aerospace and national defence industry,etc.展开更多
As the rapid development of portable and wearable devices,different electromagnetic interference(EMI)shielding materials with high efficiency have been desired to eliminate the resulting radiation pollution.However,li...As the rapid development of portable and wearable devices,different electromagnetic interference(EMI)shielding materials with high efficiency have been desired to eliminate the resulting radiation pollution.However,limited EMI shielding materials are successfully used in practical applications,due to the heavy thickness and absence of sufficient strength or flexibility.Herein,an ultrathin and flexible carbon nanotubes/MXene/cellulose nanofibrils composite paper with gradient and sandwich structure is constructed for EMI shielding application via a facile alternating vacuum-assisted filtration process.The composite paper exhibits outstanding mechanical properties with a tensile strength of 97.9±5.0 MPa and a fracture strain of 4.6±0.2%.Particularly,the paper shows a high electrical conductivity of 2506.6 S m?1 and EMI shielding effectiveness(EMI SE)of 38.4 dB due to the sandwich structure in improving EMI SE,and the gradient structure on regulating the contributions from reflection and absorption.This strategy is of great significance in fabricating ultrathin and flexible composite paper for highly efficient EMI shielding performance and in broadening the practical applications of MXene-based composite materials.展开更多
Objective To understand the effects of low-frequency pulsed electromagnetic fields （PEMFs） on chronic bony pain, bone mineral density （BMD）, bone strength and biochemical markers of bone metabolism in the patients...Objective To understand the effects of low-frequency pulsed electromagnetic fields （PEMFs） on chronic bony pain, bone mineral density （BMD）, bone strength and biochemical markers of bone metabolism in the patients of osteoporosis. Data sources Using the key words “pulsed electromagnetic fields” and “osteoporosis”, we searched the PubMed for related studies published in English from January 1996 to December 2007. We also searched the China National Knowledge Infrastructure （CNKI） for studies published in Chinese from January 1996 to December 2007.Study selection Inclusion criteria： （1） all articles which referred to the effects of low-frequency pulsed magnetic fields on osteoporosis either in primary osteoporosis or secondary osteoporosis; （2） either observational studies or randomized controlled studies. Exclusion criteria： （1） articles on experimental studies about osteoporosis; （2） repetitive studies; （3） case reports; （4） meta analysis.Results Totally 111 related articles were collected, 101 of them were published in Chinese, 10 were in English. Thirty-four were included and the remaining 84 were excluded.Conclusions Low-frequency PEMFs relieves the pain of primary osteoporosis quickly and efficiently, enhances bone formation and increases BMD of secondary osteoporosis. But the effects of PEMFs on bone mineral density of primary osteoporosis and bone resorption were controversial.展开更多
Highly thermal conductivity materials with excellent electromagnetic interference shielding and Joule heating performances are ideal for thermal management in the next generation of communication industry,artificial i...Highly thermal conductivity materials with excellent electromagnetic interference shielding and Joule heating performances are ideal for thermal management in the next generation of communication industry,artificial intelligence and wearable electronics.In this work,silver nanowires(AgNWs)are prepared using silver nitrate as the silver source and ethylene glycol as the solvent and reducing agent,and boron nitride(BN)is performed to prepare BN nanosheets(BNNS)with the help of isopropyl alcohol and ultrasonication-assisted peeling method,which are compounded with aramid nanofibers(ANF)prepared by chemical dissociation,respectively,and the(BNNS/ANF)-(AgNWs/ANF)thermal conductivity and electromagnetic interference shielding composite films with Janus structures are prepared by the"vacuum-assisted filtration and hot-pressing"method.Janus(BNNS/ANF)-(AgNWs/ANF)composite films exhibit"one side insulating,one side conducting"performance,the surface resistivity of the BNNS/ANF surface is 4.7×10^(13) Ω,while the conductivity of the AgNWs/ANF surface is 5,275 S/cm.And Janus(BNNS/ANF)-(AgNWs/ANF)composite film with thickness of 95 pm has a high in-plane thermal conductivity coefficient of 8.12 W/(m·K)and superior electromagnetic interference shielding effectiveness of 70 dB.The obtained composite film also has excellent tensile strength of 122.9 MPa and tensile modulus and 2.7 GPa.It also has good temperature-voltage response characteristics(high Joule heating temperature at low supply voltage(5 V,215.0℃),fast response time(10 s)),excellent electrical stability and reliability(stable and constant real-time relative resistance under up to 300 cycles and 1,500 s of tensile-bending fatigue work tests).展开更多
With the increasing applications of novel materials and structures in new-generation aircraft,conventional joining techniques in aircraft component assembly are greatly challenged.To meet those challenges,the electrom...With the increasing applications of novel materials and structures in new-generation aircraft,conventional joining techniques in aircraft component assembly are greatly challenged.To meet those challenges,the electromagnetic riveting(EMR)technique was developed as an advanced joining tool,which exhibits obvious advantages in the assembly of new-generation aircraft.In this paper,the riveting principle of EMR was analyzed,and its development history and status were presented in detail.Then,equipment features of three typical EMR systems were given.Moreover,three important applications of EMR were covered,i.e.,composite structure riveting,titanium rivet and large-size aluminum rivet riveting,and interference fit bolt installation.Specially,a novel strengthening method for mechanical linking holes based on EMR was also presented,which can significantly improve the fatigue behaviors of mechanical joints.Finally,open questions in the EMR field were discussed,and some recommendations for future work were also made.This paper can be useful for optimizing the joint designs of aircraft components and improving the level of aircraft maintenance.展开更多
Flexible multifunctional polymer-based electromagnetic interference(EMI)shielding composite films have important application values in the fields of 5G communication technology,wearable electronic devices and artifici...Flexible multifunctional polymer-based electromagnetic interference(EMI)shielding composite films have important application values in the fields of 5G communication technology,wearable electronic devices and artificial intelligence.In this work,Fe_(3)O_(4)/polyamic acid(PAA)nanofiber films are prepared by in-situ polymerization and electrospinning technology,and Ti_(3)C_(2)T_(x)nanosheets are deposited on the surface of the Fe_(3)O_(4)/PAA nanofiber films via vacuum-assisted filtration.Then,Janus Ti_(3)C_(2)T_(x)-(Fe_(3)O_(4)/polyimide(PI))composite films are obtained by thermal imidization.The two sides of the Janus films exhibit completely different properties.The Fe_(3)O_(4)/PI side has excellent hydrophobicity and insulation property,and the Ti_(3)C_(2)T_(x)side has hydrophilicity and terrific conductivity.When the mass fraction of Ti_(3)C_(2)T_(x)is 80 wt.%,the Janus Ti_(3)C_(2)T_(x)-(Fe_(3)O_(4)/PI)composite film has excellent EMI shielding performances and mechanical properties,with EMI shielding effectiveness,tensile strength and Young’s modulus reaching 66 dB,114.5 MPa and 5.8 GPa,respectively.At the same time,electromagnetic waves show different absorption shielding effectiveness(SEA)when incident from two sides of the Janus films.When the electromagnetic waves are incident from the Fe_(3)O_(4)/PI side,the SEA of the Janus film is 58 dB,much higher than that when the electromagnetic waves are incident from the Ti_(3)C_(2)T_(x)side(39 dB).In addition,the Ti_(3)C_(2)T_(x)side of the Janus Ti_(3)C_(2)T_(x)-(Fe_(3)O_(4)/PI)composite films also has excellent electrothermal and photothermal conversion performances.When the applied voltage is 4 V,the stable surface temperature reaches 108°C;when it is irradiated by simulated sunlight with power density of 200 mW/cm2,the stable surface temperature reaches 95℃.展开更多
Multiple hetero-interfaces would strengthen interfacial polarization and boost electromagnetic wave absorption,but still remain the formidable challenges in decreasing filler loadings.Herein,sandwich NC@Co/NC@MnO_(2)c...Multiple hetero-interfaces would strengthen interfacial polarization and boost electromagnetic wave absorption,but still remain the formidable challenges in decreasing filler loadings.Herein,sandwich NC@Co/NC@MnO_(2)composites with hollow cavity,multiple hetero-interfaces,and hierarchical structures have been fabricated via the cooperative processes of self-sacrifice strategy and sequential hydrothermal reaction.In the sandwich composites,middle magnetic components(Co/NC)are wrapped by inner N-doped carbon(NC)matrix and outer hierarchical MnO_(2)nanosheets.Importantly,hollow engineering of sandwich composites with multiple hetero-interfaces greatly facilitates the enhancement of absorption bandwidth without sacrificing the absorption intensity.The maximum reflection loss of sandwich NC@Co/NC@MnO_(2)composites reaches-44.8 dB at 2.5 mm and the effective bandwidths is achieved as wide as 9.6 GHz at 2.3 mm.These results provide us a new insight into preparing efficient electromagnetic wave absorbers by interface engineering and hollow construction.展开更多
The rapid development of aerospace weapons and equipment,wireless base stations and 5G communication technologies has put forward newer and higher requirements for the comprehensive performances of polymer-based elect...The rapid development of aerospace weapons and equipment,wireless base stations and 5G communication technologies has put forward newer and higher requirements for the comprehensive performances of polymer-based electromagnetic interference(EMI)shielding composites.However,most of currently prepared polymer-based EMI shielding composites are still difficult to combine high performance and multi-functionality.In response to this,based on the research works of relevant researchers as well as our research group,three possible directions to break through the above bottlenecks are proposed,including construction of efficient conductive networks,optimization of multi-interfaces for lightweight and multifunction compatibility design.The future development trends in three directions are prospected,and it is hoped to provide certain theoretical basis and technical guidance for the preparation,research and development of polymer-based EMI shielding composites.展开更多
基金the Foundation of National Natural Science Foundation of China(51773169 and 51973173)the Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province of China(2019JC-11)+2 种基金the Natural Science Basic Research Plan in Shaanxi Province of China(2020JQ-164)Y.Q.Guo thanks the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(CX202055)Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars.
文摘In order to ensure the operational reliability and infor-mation security of sophisticated electronic components and to protect human health,efficient electromagnetic interference(EMI)shielding materials are required to attenuate electromagnetic wave energy.In this work,the cellulose solution is obtained by dissolving cotton through hydrogen bond driving self-assembly using sodium hydroxide(NaOH)/urea solution,and cellulose aerogels(CA)are prepared by gelation and freeze-drying.Then,the cellulose carbon aerogel@reduced graphene oxide aerogels(CCA@rGO)are prepared by vacuum impregnation,freeze-drying followed by thermal annealing,and finally,the CCA@rGO/polydimethylsiloxane(PDMS)EMI shielding composites are prepared by backfilling with PDMS.Owing to skin-core structure of CCA@rGO,the complete three-dimensional(3D)double-layer con-ductive network can be successfully constructed.When the loading of CCA@rGO is 3.05 wt%,CCA@rGO/PDMS EMI shielding composites have an excellent EMI shielding effectiveness(EMI SE)of 51 dB,which is 3.9 times higher than that of the co-blended CCA/rGO/PDMS EMI shielding composites(13 dB)with the same loading of fillers.At this time,the CCA@rGO/PDMS EMI shielding composites have excellent thermal stability(T_(HRI) of 178.3℃)and good thermal conductivity coefficient(λ of 0.65 W m^(-1) K^(-1)).Excellent comprehensive performance makes CCA@rGO/PDMS EMI shielding composites great prospect for applications in lightweight,flexible EMI shielding composites.
文摘在中高压大容量的工作环境下,有源电力滤波器(active power filter,APF)谐波抑制性能及产生的电磁干扰受到主电路功率半导体器件开关频率的制约。提出一种适用于中高压混合型并联有源电力滤波器的新型滑模控制方法。该方法对电网电流和APF直流母线中点电位进行解耦跟踪控制,并将对状态变量的跟踪控制和脉宽调制(pulse width modulation,PWM)统一起来,在相同的谐波抑制精度下,可实现对开关频率的优化,将其约束在较低的确定频带内。仿真和实验结果证明,该滑模控制方法可以有效抑制由电网电压畸变和非线性负载引起的谐波电流,同时具有电磁干扰小的优点。
基金The authors are grateful for the support and funding from the Foundation of National Natural Science Foundation of China(51903145 and 51973173)Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province of China(2019JC-11)+1 种基金Fundamental Research Funds for the Central Universities(D5000210627)This work is also financially supported by Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars.
文摘With the widespread application of electronic communication technology,the resulting electromagnetic radiation pollution has been significantly increased.Metal matrix electromagnetic interference(EMI)shielding materials have disadvantages such as high density,easy corrosion,difficult processing and high price,etc.Polymer matrix EMI shielding composites possess light weight,corrosion resistance and easy processing.However,the current polymer matrix composites present relatively low electrical conductivity and poor EMI shielding performance.This review firstly discusses the key concept,loss mechanism and test method of EMI shielding.Then the current development status of EMI shielding materials is summarized,and the research progress of polymer matrix EMI shielding composites with different structures is illustrated,especially for their preparation methods and evaluation.Finally,the corresponding key scientific and technical problems are proposed,and their development trend is also prospected.
基金supported by the Foundation of National Natural Science Foundation of China(51973173)Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province of China(2019JC-11)+2 种基金Space Supporting Fund from China Aerospace Science and Industry Corporation(2019-HT-XG)Foundation of Aeronautics Science Fund(2017ZF53071)the School-enterprise Collaborative Innovation Fund for Graduate Students of Northwestern Polytechnical University(XQ201913)。
文摘Renewable porous biochar and 2 D MXene have attracted significant attention in high-end electromagnetic interference(EMI)shielding fields,due to unique orderly structures and excellent electrical conductivity(r)value.In this work,the wood-derived porous carbon(WPC)skeleton from natural wood was performed as a template.And excellent conductive and ultra-light 3D MXene aerogel was then constructed to prepare the MXene aerogel/WPC composites,based on highly ordered honeycomb cells inner WPC as a microreactor.Higher carbonization temperature is more conducive to the graphitization degree of natural wood.MXene aerogel/WPC composites achieve the optimal EMI SE value of up to 71.3 d B at density as low as 0.197 g/cm^3.Such wall-like"mortar-brick"structures(WPC skeleton as"mortar"and MXene aerogel as"brick")not only effectively solve the unstable structure problem of MXene aerogel networks,but also greatly prolong the transmission paths of the electromagnetic waves and dissipate the incident electromagnetic waves in the form of heat and electric energy,thereby exhibiting the superior EMI shielding performance.In addition,MXene aerogel/WPC composites also exhibit good anisotropic compressive strength,excellent thermal insulation and flame retardant properties.Such ultra-light,green and efficient multi-functional bio-carbon-based composites have great application potential in the high-end EMI shielding fields of aerospace and national defence industry,etc.
基金financial support from the National Natural Science Foundation of China(31771081,51472259)the Science and Technology Commission of Shanghai Municipality(18ZR1445100)Beijing Forestry University Outstanding Young Talent Cultivation Project(2019JQ03014).
文摘As the rapid development of portable and wearable devices,different electromagnetic interference(EMI)shielding materials with high efficiency have been desired to eliminate the resulting radiation pollution.However,limited EMI shielding materials are successfully used in practical applications,due to the heavy thickness and absence of sufficient strength or flexibility.Herein,an ultrathin and flexible carbon nanotubes/MXene/cellulose nanofibrils composite paper with gradient and sandwich structure is constructed for EMI shielding application via a facile alternating vacuum-assisted filtration process.The composite paper exhibits outstanding mechanical properties with a tensile strength of 97.9±5.0 MPa and a fracture strain of 4.6±0.2%.Particularly,the paper shows a high electrical conductivity of 2506.6 S m?1 and EMI shielding effectiveness(EMI SE)of 38.4 dB due to the sandwich structure in improving EMI SE,and the gradient structure on regulating the contributions from reflection and absorption.This strategy is of great significance in fabricating ultrathin and flexible composite paper for highly efficient EMI shielding performance and in broadening the practical applications of MXene-based composite materials.
基金This work was supported by a grant from the National Natural Science Foundation of China （No. 30672215）.
文摘Objective To understand the effects of low-frequency pulsed electromagnetic fields （PEMFs） on chronic bony pain, bone mineral density （BMD）, bone strength and biochemical markers of bone metabolism in the patients of osteoporosis. Data sources Using the key words “pulsed electromagnetic fields” and “osteoporosis”, we searched the PubMed for related studies published in English from January 1996 to December 2007. We also searched the China National Knowledge Infrastructure （CNKI） for studies published in Chinese from January 1996 to December 2007.Study selection Inclusion criteria： （1） all articles which referred to the effects of low-frequency pulsed magnetic fields on osteoporosis either in primary osteoporosis or secondary osteoporosis; （2） either observational studies or randomized controlled studies. Exclusion criteria： （1） articles on experimental studies about osteoporosis; （2） repetitive studies; （3） case reports; （4） meta analysis.Results Totally 111 related articles were collected, 101 of them were published in Chinese, 10 were in English. Thirty-four were included and the remaining 84 were excluded.Conclusions Low-frequency PEMFs relieves the pain of primary osteoporosis quickly and efficiently, enhances bone formation and increases BMD of secondary osteoporosis. But the effects of PEMFs on bone mineral density of primary osteoporosis and bone resorption were controversial.
基金The authors are grateful for the support and funding from the Guangdong Basic and Applied Basic Research Foundation(No.2019B1515120093)Foundation of National Natural Science Foundation of China(Nos.U21A2093 and 51973173)Technological Base Scientific Research Projects(Highly Thermal conductivity Nonmetal Materials).
文摘Highly thermal conductivity materials with excellent electromagnetic interference shielding and Joule heating performances are ideal for thermal management in the next generation of communication industry,artificial intelligence and wearable electronics.In this work,silver nanowires(AgNWs)are prepared using silver nitrate as the silver source and ethylene glycol as the solvent and reducing agent,and boron nitride(BN)is performed to prepare BN nanosheets(BNNS)with the help of isopropyl alcohol and ultrasonication-assisted peeling method,which are compounded with aramid nanofibers(ANF)prepared by chemical dissociation,respectively,and the(BNNS/ANF)-(AgNWs/ANF)thermal conductivity and electromagnetic interference shielding composite films with Janus structures are prepared by the"vacuum-assisted filtration and hot-pressing"method.Janus(BNNS/ANF)-(AgNWs/ANF)composite films exhibit"one side insulating,one side conducting"performance,the surface resistivity of the BNNS/ANF surface is 4.7×10^(13) Ω,while the conductivity of the AgNWs/ANF surface is 5,275 S/cm.And Janus(BNNS/ANF)-(AgNWs/ANF)composite film with thickness of 95 pm has a high in-plane thermal conductivity coefficient of 8.12 W/(m·K)and superior electromagnetic interference shielding effectiveness of 70 dB.The obtained composite film also has excellent tensile strength of 122.9 MPa and tensile modulus and 2.7 GPa.It also has good temperature-voltage response characteristics(high Joule heating temperature at low supply voltage(5 V,215.0℃),fast response time(10 s)),excellent electrical stability and reliability(stable and constant real-time relative resistance under up to 300 cycles and 1,500 s of tensile-bending fatigue work tests).
基金funded by the Major National Research Project of Numerical Control Machine and Basic Manufacturing Equipment of China(No.2016ZX04002004-008).
文摘With the increasing applications of novel materials and structures in new-generation aircraft,conventional joining techniques in aircraft component assembly are greatly challenged.To meet those challenges,the electromagnetic riveting(EMR)technique was developed as an advanced joining tool,which exhibits obvious advantages in the assembly of new-generation aircraft.In this paper,the riveting principle of EMR was analyzed,and its development history and status were presented in detail.Then,equipment features of three typical EMR systems were given.Moreover,three important applications of EMR were covered,i.e.,composite structure riveting,titanium rivet and large-size aluminum rivet riveting,and interference fit bolt installation.Specially,a novel strengthening method for mechanical linking holes based on EMR was also presented,which can significantly improve the fatigue behaviors of mechanical joints.Finally,open questions in the EMR field were discussed,and some recommendations for future work were also made.This paper can be useful for optimizing the joint designs of aircraft components and improving the level of aircraft maintenance.
基金supports from the National Natural Science Foundation of China(Nos.U21A2093 and 51903145)Fundamental Research Funds for the Central Universities(No.D5000210627)+1 种基金Y.L.Z.would like to thank the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX2021107)This work is also financially supported by Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars.
文摘Flexible multifunctional polymer-based electromagnetic interference(EMI)shielding composite films have important application values in the fields of 5G communication technology,wearable electronic devices and artificial intelligence.In this work,Fe_(3)O_(4)/polyamic acid(PAA)nanofiber films are prepared by in-situ polymerization and electrospinning technology,and Ti_(3)C_(2)T_(x)nanosheets are deposited on the surface of the Fe_(3)O_(4)/PAA nanofiber films via vacuum-assisted filtration.Then,Janus Ti_(3)C_(2)T_(x)-(Fe_(3)O_(4)/polyimide(PI))composite films are obtained by thermal imidization.The two sides of the Janus films exhibit completely different properties.The Fe_(3)O_(4)/PI side has excellent hydrophobicity and insulation property,and the Ti_(3)C_(2)T_(x)side has hydrophilicity and terrific conductivity.When the mass fraction of Ti_(3)C_(2)T_(x)is 80 wt.%,the Janus Ti_(3)C_(2)T_(x)-(Fe_(3)O_(4)/PI)composite film has excellent EMI shielding performances and mechanical properties,with EMI shielding effectiveness,tensile strength and Young’s modulus reaching 66 dB,114.5 MPa and 5.8 GPa,respectively.At the same time,electromagnetic waves show different absorption shielding effectiveness(SEA)when incident from two sides of the Janus films.When the electromagnetic waves are incident from the Fe_(3)O_(4)/PI side,the SEA of the Janus film is 58 dB,much higher than that when the electromagnetic waves are incident from the Ti_(3)C_(2)T_(x)side(39 dB).In addition,the Ti_(3)C_(2)T_(x)side of the Janus Ti_(3)C_(2)T_(x)-(Fe_(3)O_(4)/PI)composite films also has excellent electrothermal and photothermal conversion performances.When the applied voltage is 4 V,the stable surface temperature reaches 108°C;when it is irradiated by simulated sunlight with power density of 200 mW/cm2,the stable surface temperature reaches 95℃.
基金support from the National Natural Science Foundation of China(No.U21A2093)Natural Science Foundation of Shaanxi Province(No.2022JM-260)Fundamental Research Funds for the Central Universities(No.G2022KY05109).This work is also financially supported by the Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars.We would like to thank Zhang San from Shiyanjia Lab(www.shiyanjia.com)for the VSM analysis.
文摘Multiple hetero-interfaces would strengthen interfacial polarization and boost electromagnetic wave absorption,but still remain the formidable challenges in decreasing filler loadings.Herein,sandwich NC@Co/NC@MnO_(2)composites with hollow cavity,multiple hetero-interfaces,and hierarchical structures have been fabricated via the cooperative processes of self-sacrifice strategy and sequential hydrothermal reaction.In the sandwich composites,middle magnetic components(Co/NC)are wrapped by inner N-doped carbon(NC)matrix and outer hierarchical MnO_(2)nanosheets.Importantly,hollow engineering of sandwich composites with multiple hetero-interfaces greatly facilitates the enhancement of absorption bandwidth without sacrificing the absorption intensity.The maximum reflection loss of sandwich NC@Co/NC@MnO_(2)composites reaches-44.8 dB at 2.5 mm and the effective bandwidths is achieved as wide as 9.6 GHz at 2.3 mm.These results provide us a new insight into preparing efficient electromagnetic wave absorbers by interface engineering and hollow construction.
基金The authors are grateful for the supports from the National Natural Science Foundation of China(U21A2093)Y.L.Zhang would like to thank the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(CX2021107)+1 种基金This work is also financially supported by Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin ScholarsOpen access funding provided by Shanghai Jiao Tong University
文摘The rapid development of aerospace weapons and equipment,wireless base stations and 5G communication technologies has put forward newer and higher requirements for the comprehensive performances of polymer-based electromagnetic interference(EMI)shielding composites.However,most of currently prepared polymer-based EMI shielding composites are still difficult to combine high performance and multi-functionality.In response to this,based on the research works of relevant researchers as well as our research group,three possible directions to break through the above bottlenecks are proposed,including construction of efficient conductive networks,optimization of multi-interfaces for lightweight and multifunction compatibility design.The future development trends in three directions are prospected,and it is hoped to provide certain theoretical basis and technical guidance for the preparation,research and development of polymer-based EMI shielding composites.
