Frequency selective surfaces (FSSs) have been successfully used in constructing microwave absorbers which demonstrate the ability of modifying and improving its absorbing performances. In this paper, microwave absorbe...Frequency selective surfaces (FSSs) have been successfully used in constructing microwave absorbers which demonstrate the ability of modifying and improving its absorbing performances. In this paper, microwave absorber based on ferromagnetic nano-films has been proposed and investigated with a structure similar to that of the Salisbury screen except that the resistive sheet is replaced by FSS of square patch array of the nano-film. We have explored the FSS absorber from three aspects: equivalent circuit model, electromagnetic full-wave simulation and the actual sample measurement. By carefully tuning the patch size, the thickness of the dielectric spacer and the specification of the ferromagnetic nano-film, we obtain the optimized performance of broadband microwave absorbing. Due to the light weight of the nano-films, the proposed absorbers can achieve an ultra-low surface density less than 0.25 kg/m2.展开更多
We obtain a new class of polynomial identities on the ring of n × n matrices over any commutative ring with 1 by using the Swan’s graph theoretic method [1] in the proof of Amitsur-Levitzki theorem. Let be an Eu...We obtain a new class of polynomial identities on the ring of n × n matrices over any commutative ring with 1 by using the Swan’s graph theoretic method [1] in the proof of Amitsur-Levitzki theorem. Let be an Eulerian graph with k vertices and d edges. Further let be an integer and assume that . We prore that is an PI on Mn(C). Standard and Chang [2] -Giambruno-Sehgal [3] polynomial identities are the spectial examples of our conclusions.展开更多
In this paper , we have established an intimate connection between near-nings and linear automata,and obtain the following results: 1) For a near-ring N there exists a linear GSA S with N ≌ N(S) iff (a) (N, +) is abe...In this paper , we have established an intimate connection between near-nings and linear automata,and obtain the following results: 1) For a near-ring N there exists a linear GSA S with N ≌ N(S) iff (a) (N, +) is abelian, (b) N has an identity 1, (c) There is some d ∈ Nd such that N0 is generated by {1,d};2) Let h: S → S’ be a GSA- epimorphism. Then there exists a near-ring epimorphism from N(S) to N(S’) with h(qn) = h(q)h(n) for all q ∈ Q and n ∈ N(S);3) Let A = (Q,A,B,F,G) be a GA. Then (a) Aa:=(Q(N(A)) =: Qa,A,B,F/Qa × A) is accessible, (b) Q = 0N(A), (c) A/~:= (Q/~,A,B,F~), Q~) with F^([q], a):= [F(q,a)] and G^([q], a):= G(q,a) is reduced, (d) Aa/~ is minimal.展开更多
In this paper we propose an optimal design of ultra-wideband (4 ~ 20 GHz) microwave absorbers consisting of two resistive meta-surface layers of different square patch arrays. Gradient Descent and Genetic Algorithm nu...In this paper we propose an optimal design of ultra-wideband (4 ~ 20 GHz) microwave absorbers consisting of two resistive meta-surface layers of different square patch arrays. Gradient Descent and Genetic Algorithm numerical methods are employed to optimize all the parameters through equivalent transmission line circuit model. The circuit parameters are then implemented by a multilayer including two resistive meta-surfaces of square patch structures. Two types of such absorbing structures, with the total thicknesses close to that of the known theoretical limit, are designed and their performance are verified by full wave electromagnetic simulation.展开更多
Hyperbolic polaritons are known to exist in materials with extreme anisotropy,exhibiting exotic optical properties that enable a plethora of unusual phenomena in the fields of polaritonics and photonics.However,achiev...Hyperbolic polaritons are known to exist in materials with extreme anisotropy,exhibiting exotic optical properties that enable a plethora of unusual phenomena in the fields of polaritonics and photonics.However,achieving simultaneous low-dimensionality,high-speed controllability,and on-demand reconfigurability of the polaritons remains unexplored despite their excellent potential in light-matter interactions,photonic integrated circuits,and optoelectronic devices.Here,we propose a metasurface approach to integrating artificially engineered electromagnetic anisotropy with fast-controllable electronic elements,offering a new route to realize active topological polaritons.Experiments showcase the proposed reconfigurable metasurface can support real-time transitions of designer polaritons from elliptical to flat,and then to hyperbolic and circular isofrequency contours.Correspondingly,the in-plane surface wavefront undergoes the transitions from convex to collimating,concave,and eventually back to convex.By exploiting the topological variations in polariton dispersions,we observe intriguing phenomena of controllable field canalization and tunable planar focusing.Furthermore,we report the concept of a planar reconfigurable integrated polariton circuit by spatially tailoring the distributions of polariton isofrequency contours,unveiling rich dispersion engineering possibilities and active control capabilities.We may provide an inspiring platform for developing planar active plasmonic devices with potential applications in subdiffraction-resolution imaging,sensing,and information processing.展开更多
Dynamic manipulation of electromagnetic(EM)waves with multiple degrees of freedom plays an essential role in enhancing information processing.Currently,an enormous challenge is to realize directional terahertz(THz)hol...Dynamic manipulation of electromagnetic(EM)waves with multiple degrees of freedom plays an essential role in enhancing information processing.Currently,an enormous challenge is to realize directional terahertz(THz)holography.Recently,it was demonstrated that Janus metasurfaces could produce distinct responses to EM waves from two opposite incident directions,making multiplexed dynamic manipulation of THz waves possible.Herein,we show that thermally activated THz Janus metasurfaces integrating with phase change materials on the meta-atoms can produce asymmetric transmission with the designed phase delays.Such reconfigurable Janus metasurfaces can achieve asymmetric focusing of THz wave and directional THz holography with free-space image projections,and particularly the information can be manipulated via temperature and incident THz wave direction.This work not only offers a common strategy for realizing the reconfigurability of Janus metasurfaces,but also shows possible applications in THz optical information encryption,data storage,and smart windows.展开更多
Metasurfaces,ultrathin two-dimensional version of metamaterials,have attracted tremendous attention due to their exotic capabilities to freely manipulate electromagnetic waves.By incorporating various tunable material...Metasurfaces,ultrathin two-dimensional version of metamaterials,have attracted tremendous attention due to their exotic capabilities to freely manipulate electromagnetic waves.By incorporating various tunable materials or elements into metasurface designs,reconfigurable metasurfaces and related metadevices with functionalities controlled by external stimuli can be realized,opening a new avenue to achieving dynamic manipulation of electromagnetic waves.Recently,based on the tunable metasurface concept,reconfigurable intelligent surfaces(RISs)have received significant attention and have been regarded as a promising emerging technology for future wireless communication due to their potential to enhance the capacity and coverage of wireless networks by smartly reconfiguring the wireless propagation environment.Here,in this article,we first focus on technical issues of RIS system implementation by reviewing the existing research contributions,paying special attention to designs in the microwave regime.Then,we showcase our recent attempts to practically demonstrate RIS systems in real-world applications,including deploying reflective RIS systems in indoor scenarios to enhance the wireless network coverage and utilizing intelligent omni-metasurfaces to improve both indoor and through-wall wireless communication quality.Finally,we give our own perspectives on possible future directions and existing challenges for RISs toward a truly commercial intelligent technology platform.展开更多
Reconfigurable intelligent surface(RIS)is emerged as a promising technique to solve the challenges faced by future wireless communication networks.Although the most commonly used electrically-controlled RISs can achie...Reconfigurable intelligent surface(RIS)is emerged as a promising technique to solve the challenges faced by future wireless communication networks.Although the most commonly used electrically-controlled RISs can achieve millisecond-scale speed of dynamic switch,they have a large number of microwave circuit elements(such as PIN diodes or varactors)which will bring non-negligible insertion loss,and the complicity of the bias network to electrically addressing each element will increase with the expansion of the RIS aperture.Aiming at further reducing the fabrication cost and power consumption,herein an electromechanical RIS used for sub-6G wireless communication is proposed.The electromechanical RIS is designed with a passive metasurface and step-motor driver modules,providing simultaneous high-efficiency reflection(over 80%)and continuous reflection phase coverage of 360.Through electromechanical control,the RIS system can realize different reflective wavefront shaping,and has been employed in the indoor sub-6G wireless environment demonstrating a maximum signal improvement of 8.3 dB.The proposed electromechanical RIS is particularly useful for wireless signal enhancement in static blind area,and has the obvious advantage of not requiring continuous power supply after the RIS being regulated.Therefore,it greatly reduces the overall cost and power consumption which may have potentials in indoor application scenarios for improving wireless communication performance.展开更多
A facile strategy was developed to fabricate flexible polyurethane(PU)foam composites with exceptional flame retardancy.The approach involves the incorporation of graphene oxide(GO)into a silicone resin(SiR)solution,w...A facile strategy was developed to fabricate flexible polyurethane(PU)foam composites with exceptional flame retardancy.The approach involves the incorporation of graphene oxide(GO)into a silicone resin(SiR)solution,which is then deposited onto a PU foam surface via the dip-coating technique and cured.Fourier-transform infrared spectroscopy,scanning electron microscopy,and Raman spectroscopy measurements demonstrated that the SiR and GO were successfully coated onto the PU skeleton and the intrinsic porous structure of the PU foam remained intact.The effects of SiR and GO on the mechanical and thermal stability and flame retardancy of PU composites were evaluated through compression tests,thermogravimetric analysis,vertical combustion tests,and the limiting oxygen index.The measurement results revealed that the composites(PU@SiR-GO)showed superior flame retardancy and thermal and mechanical stability compared to pristine PU or PU coated with SiR alone.The mechanical and thermal stability and the flame-retardant properties of the PU composites were enhanced significantly with increasing GO content.Based on the composition,microstructure,and surface morphology of PU@SiR-GO composites before and after combustion tests,a possible flame-retardance mechanism is proposed.This work provides a simple and effective strategy for fabricating flame retardant composites with improved mechanical performance.展开更多
The principles and characteristics of rapid single flux quantum (RSFQ) circ- uits are discussed. According to these theories, we have designed RSFQ inverter, XOR cell and shift registers relative to the pseudo random ...The principles and characteristics of rapid single flux quantum (RSFQ) circ- uits are discussed. According to these theories, we have designed RSFQ inverter, XOR cell and shift registers relative to the pseudo random generator. Based on these cells, the RSFQ pseudo random generator is given. Compared with the simulation result of another mathematical model that is established by MATLAB, the design of the RSFQ pseudo random generator is proved to be reasonable and meets our expectations.展开更多
文摘Frequency selective surfaces (FSSs) have been successfully used in constructing microwave absorbers which demonstrate the ability of modifying and improving its absorbing performances. In this paper, microwave absorber based on ferromagnetic nano-films has been proposed and investigated with a structure similar to that of the Salisbury screen except that the resistive sheet is replaced by FSS of square patch array of the nano-film. We have explored the FSS absorber from three aspects: equivalent circuit model, electromagnetic full-wave simulation and the actual sample measurement. By carefully tuning the patch size, the thickness of the dielectric spacer and the specification of the ferromagnetic nano-film, we obtain the optimized performance of broadband microwave absorbing. Due to the light weight of the nano-films, the proposed absorbers can achieve an ultra-low surface density less than 0.25 kg/m2.
文摘We obtain a new class of polynomial identities on the ring of n × n matrices over any commutative ring with 1 by using the Swan’s graph theoretic method [1] in the proof of Amitsur-Levitzki theorem. Let be an Eulerian graph with k vertices and d edges. Further let be an integer and assume that . We prore that is an PI on Mn(C). Standard and Chang [2] -Giambruno-Sehgal [3] polynomial identities are the spectial examples of our conclusions.
文摘In this paper , we have established an intimate connection between near-nings and linear automata,and obtain the following results: 1) For a near-ring N there exists a linear GSA S with N ≌ N(S) iff (a) (N, +) is abelian, (b) N has an identity 1, (c) There is some d ∈ Nd such that N0 is generated by {1,d};2) Let h: S → S’ be a GSA- epimorphism. Then there exists a near-ring epimorphism from N(S) to N(S’) with h(qn) = h(q)h(n) for all q ∈ Q and n ∈ N(S);3) Let A = (Q,A,B,F,G) be a GA. Then (a) Aa:=(Q(N(A)) =: Qa,A,B,F/Qa × A) is accessible, (b) Q = 0N(A), (c) A/~:= (Q/~,A,B,F~), Q~) with F^([q], a):= [F(q,a)] and G^([q], a):= G(q,a) is reduced, (d) Aa/~ is minimal.
文摘In this paper we propose an optimal design of ultra-wideband (4 ~ 20 GHz) microwave absorbers consisting of two resistive meta-surface layers of different square patch arrays. Gradient Descent and Genetic Algorithm numerical methods are employed to optimize all the parameters through equivalent transmission line circuit model. The circuit parameters are then implemented by a multilayer including two resistive meta-surfaces of square patch structures. Two types of such absorbing structures, with the total thicknesses close to that of the known theoretical limit, are designed and their performance are verified by full wave electromagnetic simulation.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.62271243 and 62071215)the Fundamental Research Funds for the Central Universities+2 种基金the Jiangsu Provincial Key Research and Development Program(Grant No.BE2023084)the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe Jiangsu Provincial Key Laboratory of Advanced Manipulating Technique of Electromagnetic Wave
文摘Hyperbolic polaritons are known to exist in materials with extreme anisotropy,exhibiting exotic optical properties that enable a plethora of unusual phenomena in the fields of polaritonics and photonics.However,achieving simultaneous low-dimensionality,high-speed controllability,and on-demand reconfigurability of the polaritons remains unexplored despite their excellent potential in light-matter interactions,photonic integrated circuits,and optoelectronic devices.Here,we propose a metasurface approach to integrating artificially engineered electromagnetic anisotropy with fast-controllable electronic elements,offering a new route to realize active topological polaritons.Experiments showcase the proposed reconfigurable metasurface can support real-time transitions of designer polaritons from elliptical to flat,and then to hyperbolic and circular isofrequency contours.Correspondingly,the in-plane surface wavefront undergoes the transitions from convex to collimating,concave,and eventually back to convex.By exploiting the topological variations in polariton dispersions,we observe intriguing phenomena of controllable field canalization and tunable planar focusing.Furthermore,we report the concept of a planar reconfigurable integrated polariton circuit by spatially tailoring the distributions of polariton isofrequency contours,unveiling rich dispersion engineering possibilities and active control capabilities.We may provide an inspiring platform for developing planar active plasmonic devices with potential applications in subdiffraction-resolution imaging,sensing,and information processing.
基金This study was supported by the National Key Research and Development Program of China(2017YFA0700202,2021YFB2800701)National Nature Science Foundation of China(62288101,91963128,62071215,62071217,62027807,62035014)Fundamental Research Funds for the Central Universities,and Research Fund for Jiangsu Key Laboratory of Advanced Techniques for Manipulating Electromagnetic Waves.J.W.acknowledges the support from Xiaomi Young Scholar Program.
文摘Dynamic manipulation of electromagnetic(EM)waves with multiple degrees of freedom plays an essential role in enhancing information processing.Currently,an enormous challenge is to realize directional terahertz(THz)holography.Recently,it was demonstrated that Janus metasurfaces could produce distinct responses to EM waves from two opposite incident directions,making multiplexed dynamic manipulation of THz waves possible.Herein,we show that thermally activated THz Janus metasurfaces integrating with phase change materials on the meta-atoms can produce asymmetric transmission with the designed phase delays.Such reconfigurable Janus metasurfaces can achieve asymmetric focusing of THz wave and directional THz holography with free-space image projections,and particularly the information can be manipulated via temperature and incident THz wave direction.This work not only offers a common strategy for realizing the reconfigurability of Janus metasurfaces,but also shows possible applications in THz optical information encryption,data storage,and smart windows.
基金supported by the National Natural Science Foundation of China(Grant Nos.62271243,62071215,91963128,and 61731010)the National Key Research and Development Program of China(Grant No.2017YFA0700201)the Joint Fund of Ministry of Education for Equipment Pre-research(Grant No.8091B032112).
文摘Metasurfaces,ultrathin two-dimensional version of metamaterials,have attracted tremendous attention due to their exotic capabilities to freely manipulate electromagnetic waves.By incorporating various tunable materials or elements into metasurface designs,reconfigurable metasurfaces and related metadevices with functionalities controlled by external stimuli can be realized,opening a new avenue to achieving dynamic manipulation of electromagnetic waves.Recently,based on the tunable metasurface concept,reconfigurable intelligent surfaces(RISs)have received significant attention and have been regarded as a promising emerging technology for future wireless communication due to their potential to enhance the capacity and coverage of wireless networks by smartly reconfiguring the wireless propagation environment.Here,in this article,we first focus on technical issues of RIS system implementation by reviewing the existing research contributions,paying special attention to designs in the microwave regime.Then,we showcase our recent attempts to practically demonstrate RIS systems in real-world applications,including deploying reflective RIS systems in indoor scenarios to enhance the wireless network coverage and utilizing intelligent omni-metasurfaces to improve both indoor and through-wall wireless communication quality.Finally,we give our own perspectives on possible future directions and existing challenges for RISs toward a truly commercial intelligent technology platform.
基金supported by National Natural Science Foundation of China(62071215,62271243,91963128)National Key Research and Development Program of China(2017YFA0700201)the Joint Fund of Ministry of Education for Equipment Pre-research(8091B032112),Priority Academic Program Development of Jiangsu Higher Education Institutions,Fundamental Research Funds for the Central Universities and Jiangsu Provincial Key Laboratory of Advanced Manipulating Technique of Electromagnetic Wave.
文摘Reconfigurable intelligent surface(RIS)is emerged as a promising technique to solve the challenges faced by future wireless communication networks.Although the most commonly used electrically-controlled RISs can achieve millisecond-scale speed of dynamic switch,they have a large number of microwave circuit elements(such as PIN diodes or varactors)which will bring non-negligible insertion loss,and the complicity of the bias network to electrically addressing each element will increase with the expansion of the RIS aperture.Aiming at further reducing the fabrication cost and power consumption,herein an electromechanical RIS used for sub-6G wireless communication is proposed.The electromechanical RIS is designed with a passive metasurface and step-motor driver modules,providing simultaneous high-efficiency reflection(over 80%)and continuous reflection phase coverage of 360.Through electromechanical control,the RIS system can realize different reflective wavefront shaping,and has been employed in the indoor sub-6G wireless environment demonstrating a maximum signal improvement of 8.3 dB.The proposed electromechanical RIS is particularly useful for wireless signal enhancement in static blind area,and has the obvious advantage of not requiring continuous power supply after the RIS being regulated.Therefore,it greatly reduces the overall cost and power consumption which may have potentials in indoor application scenarios for improving wireless communication performance.
基金This work was supported by the National Key Research and Development Program(Grant No.2017YFB0307700)the Department of Scientific and Technology of Zhejiang Province(LGG18E030007,LGG19E030007)+1 种基金the Project for the Innovation of High Level Returned Overseas Scholars(or team)in Hangzhou.We also acknowledge the support from Collaborative Innovation Center of Zhejiang Province for the Manufacture of Fluorine and Silicone Fine Chemicals and Materials(FSi2018A028,FSi2018B004)professional development project for domestic visiting scholars in universities(FX2017054).
文摘A facile strategy was developed to fabricate flexible polyurethane(PU)foam composites with exceptional flame retardancy.The approach involves the incorporation of graphene oxide(GO)into a silicone resin(SiR)solution,which is then deposited onto a PU foam surface via the dip-coating technique and cured.Fourier-transform infrared spectroscopy,scanning electron microscopy,and Raman spectroscopy measurements demonstrated that the SiR and GO were successfully coated onto the PU skeleton and the intrinsic porous structure of the PU foam remained intact.The effects of SiR and GO on the mechanical and thermal stability and flame retardancy of PU composites were evaluated through compression tests,thermogravimetric analysis,vertical combustion tests,and the limiting oxygen index.The measurement results revealed that the composites(PU@SiR-GO)showed superior flame retardancy and thermal and mechanical stability compared to pristine PU or PU coated with SiR alone.The mechanical and thermal stability and the flame-retardant properties of the PU composites were enhanced significantly with increasing GO content.Based on the composition,microstructure,and surface morphology of PU@SiR-GO composites before and after combustion tests,a possible flame-retardance mechanism is proposed.This work provides a simple and effective strategy for fabricating flame retardant composites with improved mechanical performance.
基金The National Center for Research and Development on Superconductivity of China and the National Science Fund for Distinguished Young Scholars (B) (Grant No. 69801004).
文摘The principles and characteristics of rapid single flux quantum (RSFQ) circ- uits are discussed. According to these theories, we have designed RSFQ inverter, XOR cell and shift registers relative to the pseudo random generator. Based on these cells, the RSFQ pseudo random generator is given. Compared with the simulation result of another mathematical model that is established by MATLAB, the design of the RSFQ pseudo random generator is proved to be reasonable and meets our expectations.
