Composites featuring negative permittivity have garnered significant attention for their potential in novel capacitance designs,coil-less electrical inductors,and electromagnetic shielding applications.In this study,w...Composites featuring negative permittivity have garnered significant attention for their potential in novel capacitance designs,coil-less electrical inductors,and electromagnetic shielding applications.In this study,we prepared polyvinylidene fluoride(PVDF)matrix composites filled with ZrO_(2)/C nanoparticles de-rived from metal-organic frameworks(MOFs)via a hot-pressing method.With an increase in the ZrO_(2)/C content to 30 wt.%,electrical percolation was observed,accompanied by a transition mechanism from hopping conduction to metal-like conduction.This enabled the realization of ZrO_(2)/C/PVDF composites with tailorable negative permittivity properties,attributed to the plasmonic oscillation of free electrons in the composites beyond the percolation threshold(30 wt.%).Furthermore,the permittivity transition along to a shift in the electrical behavior of the percolative composites from capacitive to inductive.We explored the regulatory mechanism behind the negative permittivity in this random composite system,and our findings highlight the potential of these tunable negative permittivity media as promising candi-dates for diverse electromagnetic applications.展开更多
Flexible composites with negative permittivity have a very broad development prospect in flexible electronics and wearable devices.Currently,how to control the negative permittivity except for from their intrinsic pro...Flexible composites with negative permittivity have a very broad development prospect in flexible electronics and wearable devices.Currently,how to control the negative permittivity except for from their intrinsic properties of components is still a challenge.In this study,the negative permittivity and frequency dispersion were adjusted by changing the heat treatment temperature.Polyvinylidene fluoride(PVDF)was selected as the flexible matrix and reduced graphene oxide(rGO)as the functional filler to prepare rGO/PVDF membranous composites.The negative permittivity was observed in rGO/PVDF composites film,and the effect of heat treatment temperature on the negative permittivity was further studied.It indicated that a higher heat treatment temperature contributed to the formation of conductive network,so as to obtaining negative permittivity.When the molding temperature was 70℃,the negative permittivity spectrum conformed to the Drude model was only observed in the composites with 35 wt%content of rGO.After the heat treatment temperature reached 180℃,when the content of rGO decreased to 25 wt%,the composites film achieved negative permittivity(~-10),which had a low-frequency dispersion in the test frequency range.The negative permittivity of in composites can be regulated by adjusting the heat treatment temperature,which promotes the application and development of flexible metamaterials in underwater sensing and detection,etc.展开更多
Phonon polaritons(PhPs)exhibit directional in-plane propagation and ultralow losses in van der Waals(vdW)crystals,offering new possibilities for controlling the flow of light at the nanoscale.However,these PhPs,includ...Phonon polaritons(PhPs)exhibit directional in-plane propagation and ultralow losses in van der Waals(vdW)crystals,offering new possibilities for controlling the flow of light at the nanoscale.However,these PhPs,including their directional propagation,are inherently determined by the anisotropic crystal structure of the host materials.Although in-plane anisotropic PhPs can be manipulated by twisting engineering,such as twisting individual vdW slabs,dynamically adjusting their propagation presents a significant challenge.The limited application of the twisted bilayer structure in bare films further restricts its usage.In this study,we present a technique in which anisotropic PhPs supported by bare biaxial vdW slabs can be actively tuned by modifying their local dielectric environment.Excitingly,we predict that the iso-frequency contour of PhPs can be reoriented to enable propagation along forbidden directions when the crystal is placed on a substrate with a moderate negative permittivity.Besides,we systematically investigate the impact of polaritonic coupling on near-field radiative heat transfer(NFRHT)between heterostructures integrated with different substrates that have negative permittivity.Our main findings reveal that through the analysis of dispersion contour and photon transmission coefficient,the excitation and reorientation of the fundamental mode facilitate increased photon tunneling,thereby enhancing heat transfer between heterostructures.Conversely,the annihilation of the fundamental mode hinders heat transfer.Furthermore,we find the enhancement or suppression of radiative energy transport depends on the relative magnitude of the slab thickness and the vacuum gap width.Finally,the effect of negative permittivity substrates on NFRHT along the[001]crystalline direction ofα-MoO3 is considered.The spectral band where the excited fundamental mode resulting from the negative permittivity substrates is shifted to the first Reststrahlen Band(RB 1)ofα-MoO_(3) and is widened,resulting in more significant enhancement of heat flux from RB 1.We anticipate our results will motivate new direction for dynamical tunability of the PhPs in photonic devices.展开更多
Negative permittivity has been widely studied in various metamaterials and percolating composites, of which the anomalous dielectric behavior was attributed to critical structural properties of building blocks.Herein,...Negative permittivity has been widely studied in various metamaterials and percolating composites, of which the anomalous dielectric behavior was attributed to critical structural properties of building blocks.Herein, mono-phase ceramics of indium tin oxides(ITO) were sintered for epsilon-negative materials in MHz-k Hz frequency regions. Electrical conductivity and complex permittivity were analyzed with DrudeLorentz oscillator model. Carriers’ characters were measured based on Hall effect and the magnitude and frequency dispersion of negative permittivity were mainly determined by carrier concentration.Temperature-dependent dielectric properties further proved the epsilon-negative behaviors were closely associated with free carriers’ collective responses. It’s found that negative permittivity of ITO ceramics was mainly caused by plasma oscillations of free carriers, while the dielectric loss was mainly attributed to conduction loss. Negative permittivity realized here was related to materials intrinsic nature and this work preliminarily determined the mechanism of negative permittivity in doped ceramics from the perspective of carriers.展开更多
The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is benefici...The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is beneficial to reduce plasma frequency so that negative permittivity is achieved in kHz region.Negative permittivity achieved by percolating composites is restricted in practicality due to its instability nature at high temperatures.To achieve temperature-stable negative permittivity in kHz region,monophase La_(1-x)Ba_(x)CoO_(3)ceramics were prepared,and the transition from dielectric to metal was elaborated in the perspective of electrical conductivity and negative permittivity.The plasma-like negative permittivity is attained in kHz region,which is interpreted by the collective oscillation of low electron density.The temperature-stable negative permittivity is based on the fact that the plasmonic state will not be undermined at high temperatures.In addition,zero-crossing behavior of real permittivity is observed in La_(0.9)Ba_(0.1)CoO_(3)sample,which provides a promising alternative to designing epsilon-near-zero materials.This work makes the La_(1-x)Ba_(x)CoO_(3)system a source material for achieving effective negative permittivity.展开更多
Recently,increasing attention has been concentrated on negative permittivity with the development of the emerging metamaterials composed of periodic array structures.However,taking facile preparation into consideratio...Recently,increasing attention has been concentrated on negative permittivity with the development of the emerging metamaterials composed of periodic array structures.However,taking facile preparation into consideration,it is important to achieve negative permittivity behavior based on materials'intrinsic properties rather than their artificially periodic structures.In this paper,we proposed to fabricate the percolating composites with copper dispersed in epoxy(EP)resin by a polymerization method to realize the negative permittivity behavior.When Cu content in the composites reached to 80 wt%,the conductivity abruptly went up by three orders of magnitudes,suggesting a percolation behavior.Below the percolation threshold,the conductivity spectra conform to Jonscher's power law;when the Cu/EP composites reached to percolating state,the conductivity gradually reduced in high frequency region due to the skin effect.It is indicated that the conductive mechanism changed from hopping conduction to electron conduction.In addition,the permittivity did not increase monotonously with the increase of Cu content in the vicinity of percolation threshold,due to the presence of leakage current.Meanwhile,the negative permittivity conforming to Drude model was observed above the percolation threshold.Further investigation revealed that there was a constitutive relationship between the permittivity and the reactance.When conductive fillers are slightly above the percolation threshold,the inductive characteristic derived from conductive percolating network leads to the negative permittivity.Such epsilon-negative materials can potentially be applied in novel electrical devices,such as high-power microwave filters,stacked capacitors,negative capacitance field effect transistors and coil-free resonators.In addition,the design strategy based on percolating composites provides an approach to epsilon-negative materials.展开更多
Metacomposites with negative permittivity usually possess huge dielectric loss,showing potential for micro-wave attenuation devices where huge heat would generate.Herein,carbon nanotube-carbon black/CaCu_(3-)Ti_(4)O_(...Metacomposites with negative permittivity usually possess huge dielectric loss,showing potential for micro-wave attenuation devices where huge heat would generate.Herein,carbon nanotube-carbon black/CaCu_(3-)Ti_(4)O_(12)(CNT-CB/CCTO)ternary metacomposites were fabricated by spark plasma sintering.The CNT-CB dualphase filler was pre-pared through electrostatic selfassembly process in order to construct an effective 3-dimensional(3D)carbon network in CCTO matrix.The percolation threshold of CNT-CB/CCTO composites was identified at filler content of 12.52 wt%which accompanied with an essential change of conduction mechanism.The negative permittivity was derived from low-frequency plasmonic state of the 3D carbon network,described by Drude model.The problem of heat transport,generally occurring in negative permittivity materials,has been solved and optimized in obtained ternary metacomposites beneftting from the substantially high thermal conductivity(9.49-2.00 W·m^(-1)·K^(-1))and diffusivity(2.74-1.22mm^(2)·s^(-1)).This work could spark significant development of practical application of metacomposites on novel electronic devices and electromagnetic apparatus.展开更多
A new quantum optical mechanism to realize simultaneously negative electric permittivity and magnetic permeability is suggested. In order to obtain a negative permeability, we choose a proper atomic configuration that...A new quantum optical mechanism to realize simultaneously negative electric permittivity and magnetic permeability is suggested. In order to obtain a negative permeability, we choose a proper atomic configuration that can dramatically enhance the contribution of the magnetic-dipole allowed transition via the atomic phase coherence. It is shown that the atomic system chosen with proper optical parameters can give rise to striking electromagnetic responses （leading to a negative refractive index） and that the atomic vapour becomes a left-handed medium in an optical frequency band. Differing from the previous schemes of artificial composite metamaterials （based on classical electromagnetic theory） to achieve the left-handed materials, which consist of anisotropic millimetre-scale composite structure units, the left-handed atomic vapour presented here is isotropic and homogeneous at the atomic-scale level. Such an advantage may be valuable in realizing the superlens （and hence perfect image） with left-handed atomic vapour.展开更多
CaCu_(3)Ti_(4)O_(12)(CCTO)ceramic nanocomposites incorporating graphene–carbon black(GRCB)fillers were fabricated by spark plasma sintering process.The percolative effects of conductive GRCB fillers on dielectric res...CaCu_(3)Ti_(4)O_(12)(CCTO)ceramic nanocomposites incorporating graphene–carbon black(GRCB)fillers were fabricated by spark plasma sintering process.The percolative effects of conductive GRCB fillers on dielectric response of GRCB/CCTO ternary metacomposites were systematically investigated.The weakly real permittivity(ε′)-negative response(ε′~−1×10^(2))was achieved which originated from weakly low-frequency plasmonic state of free carriers within constructed GRCB networks.With enhancing three-dimensional GRCB network,the plasma frequency of metacomposites increased while the damping factor decreased.Herein,theε′-negative values of metacomposites were tuned from−10^(2) to−10^(4) orders of magnitude andε′-near-zero(ENZ)frequencies from~142 to~340 MHz which substantially benefited from the moderate carrier concentration of GRCB dual fillers.The Drude model and equivalent circuit models were adopted to demonstrate dielectric and electrical characteristics.The obtained metacomposites show strong EM shielding effect along with enhanced plasmonic oscillation and even better achieving perfect EM shielding effect in ENZ media.This work achieves the tunableε′-negative andε′-near-zero response and more importantly clarifies its regulation mechanism in ceramic-based ternary metacomposites,which opens up the possibility of designing high-performance EM shielding materials based on metacomposites.展开更多
The anti-resonant phenomenon of effective electromagnetic parameters of metamaterials has aroused controversy due to negative imaginary permittivity or permeability. It is experimentally found that the negative imagin...The anti-resonant phenomenon of effective electromagnetic parameters of metamaterials has aroused controversy due to negative imaginary permittivity or permeability. It is experimentally found that the negative imaginary permittivity can occur for the natural passive materials near the Fabry Perot resonances. We reveal the nature of negative imaginary permittivity, which is correlated with the magnetoelectric coupling. The anti-resonance of permittivity is a non-inherent feature for passive materials, while it can be inherent for devices or metamaterials. Our finding validates that the negative imaginary part of effective permittivity does not contradict the second law of thermodynamics for metamaterials owing to the magnetoelectric coupling.展开更多
We take a finite dielectric photonic crystal as a homogeneous slab and have extracted the effective parameters. Our systematic study shows that the effective permittivity or permeability of dielectric photonic crystal...We take a finite dielectric photonic crystal as a homogeneous slab and have extracted the effective parameters. Our systematic study shows that the effective permittivity or permeability of dielectric photonic crystal is negative within a band gap region. This means that the band gap might act as ε-negative materials （ENMs） with ε 〈 0 and μ 〉 0, or μ-negative materials （MNMs） with ε 〉 0 and μ 〈 0. Moreover the effective parameters sensitively rely on size, surface termination, symmetry, etc. The effective parameters can be used to design full transmission tunnelling modes and amplify evanescent wave. Several cases are studied and the results show that dielectric photonic band gap can indeed mimic a single negative material （ENM or MNM） under some restrictions.展开更多
NiFe_(2)O_(4)/polypyrrole(NiFe_(2)O_(4)/PPy)nanocomposites are prepared by a simple surface-initiated polymerization method and demonstrate negative permittivity in the low frequency regions.These nanocomposites also ...NiFe_(2)O_(4)/polypyrrole(NiFe_(2)O_(4)/PPy)nanocomposites are prepared by a simple surface-initiated polymerization method and demonstrate negative permittivity in the low frequency regions.These nanocomposites also exhibit significantly enhanced electromagnetic wave(EMW)absorption property in the high frequency regions.Compared with pure PPy,the enhanced negative permittivity is observed in the NiFe_(2)O_(4)/PPy nanocomposites with a NiFe_(2)O_(4)loading of 5.0,10.0,20.0 and 40.0 wt%,indicating the formation of metal-like electrical conducting network in NiFe_(2)O_(4)/PPy nanocomposites.Moreover,the negative permittivity could be tuned by changing the NiFe_(2)O_(4)loading.The minimum reflection loss(RL)of-40.8 dB is observed in the 40.0 wt%NiFe_(2)O_(4)/PPy composites with a thickness of only 1.9 mm.The effective absorption bandwidth below-10.0 and-20.0 dB reaches 6.08 and 2.08 GHz,respectively.The enhanced EMW absorption performance benefits from the improved independence matching,EMW attenuation capacity,and synergistic effects of conduction loss,dielectric loss(interfacial and dipole polarizations)and magnetic loss(exchange and natural resonances).This research work provides a guidance for the fabrication of nanocomposites with an excellent EMW absorption.展开更多
Facing the challenges posed by exponentially increasing e-waste,the development of recyclable and tran-sient electronics has paved the way to an environmentally-friendly progression strategy,where electron-ics can dis...Facing the challenges posed by exponentially increasing e-waste,the development of recyclable and tran-sient electronics has paved the way to an environmentally-friendly progression strategy,where electron-ics can disintegrate and/or degrade into eco-friendly end products in a controlled way.Natural polymers possess cost and energy efficiency,easy modification,and fast degradation,all of which are ideal prop-erties for transient electronics.Gelatin is especially attractive due to its unique thermoreversible gelation processes,yet its huge potential as a multifunctional electronic material has not been well-researched due to its limited mechanical strength and low conductivity.Herein,we explored versatile applications of gelatin-based hydrogels through the assistance of multifunctional additives like carbon nanotubes to enhance their electromechanical performances.The optimized gelatin hydrogel displays not only a high conductivity of 0.93 S/m,electromagnetic shielding effectiveness of 39.6 dB,and tensile stress tolerance of 263 kPa,but also shows a negative permittivity phenomenon,which may find versatile applications in novel electronics.As a proof of concept,hydrogels were assembled as wearable sensors to sensitively de-tect static and dynamic pressures and strains generated by solids,liquids,and airflow,as well as diverse body movements.Furthermore,the recyclability,biocompatibility,and degradability of gelatin-based hy-drogels were well studied and analyzed.This work outlines a facile method to design multifunctional transient materials for wearable,sustainable,and eco-friendly electronics.展开更多
Percolating composites with negative permittivity can be promising candidates for metamaterials.Herein,novel all-organic composite films containing of random coil polypyrrole(PPy)and poly(-vinylidene fluoride)(PVDF)ar...Percolating composites with negative permittivity can be promising candidates for metamaterials.Herein,novel all-organic composite films containing of random coil polypyrrole(PPy)and poly(-vinylidene fluoride)(PVDF)are fabricated via a solution casting method.The random coil PPy is prepared by oxidative template assembly approach for the first time.The experimental result indicates that the negative permittivity is easily adjusted through controlling the random coil PPy contents.Especially,the random coil PPy contents exceeded 7 wt% the negative permittivity appear attributed to the formation of 3D interconnected PPy network.This facile approach not only opens a new way to preparing negative permittivity of all-organic composite films,but also points out a route to facilitate the practical applications of metamaterials.展开更多
Epsilon-near-zero(ENZ)material has been a research hotspot in recent years due to unique physical properties such as inverse Doppler effect and negative refractive index,showing great potentials in the fields of flexi...Epsilon-near-zero(ENZ)material has been a research hotspot in recent years due to unique physical properties such as inverse Doppler effect and negative refractive index,showing great potentials in the fields of flexible electronics,wearable devices,sensors,etc.The ENZ materials are mostly reported at visible,infrared and terahertz wavelengths,while the report about ENZ materials at radio frequency is rare.In this work,flexible and biocompatible poly(vinyl alcohol)/multi-walled carbon nanotubes(PVA/MWCNTs)hydrogels,which were successfully fabricated by an environmentally friendly method,were used as ENZ materials at radio frequency for the first time.Cytotoxicity experiments proved that the experimental process and products are green,environmentally friendly and biocompatible.The microstructure,crystalline structure,chemical composition and dielectric properties were investigated.Two different water states,which were free water molecules and bound water molecules,coexisted in these PVA/MWCNTs hydrogels and accounted for about 37.5 wt%and 15.9 wt%respectively by analyzing the thermogravimetric analysis curves.When the MWCNTs content reached 12 wt%and 15 wt%,the continuous conductive MWCNTs network was formed in the hydrogel,and ENZ phenomenon was observed at about 760 k Hz and 580 k Hz respectively,which was attributed to the interband transition.Considering the flexibility and non-toxicity of PVA/MWCNTs hydrogels,the ENZ properties of this structure at the radio frequency can be well used in wearable invisibility cloak,flexible electronics,skin sensors and other wearable devices.展开更多
In this paper we have investigated three external fields interacting with the four-level Y-type atomic system described by the density-matrix approach. The results show that left-handedness with zero absorption is ach...In this paper we have investigated three external fields interacting with the four-level Y-type atomic system described by the density-matrix approach. The results show that left-handedness with zero absorption is achieved. The zero absorption property displays the possibility of manipulation by varying the phase and the intensity of the coupling field. Also, the zero absorption property may be used to amplify the evanescent waves that have been lost in imaging by traditional lenses. We propose an approach to obtain a negative refractive medium with zero absorption and the possibility of enhaneeingthe imaging resolution in realizing ＇superlenses＇.展开更多
Left-hand materials have drawn increasing attention from many disciplines and found widespread application, especially in microwave engineering. A sandwiched metamaterial consisting of multi-nested square-split-ring r...Left-hand materials have drawn increasing attention from many disciplines and found widespread application, especially in microwave engineering. A sandwiched metamaterial consisting of multi-nested square-split-ring resonators on the top side and a set of wires on the back side is proposed. Scattering parameters are retrieved by high-frequency structure simulator(HFSS) software based on the finite element method. Effects of square-split-ring number on the left-hand characteristics containing negative values of permittivity, permeability, and refractive index have been intensively investigated. Simulated results show that obvious resonant left-hand characteristics could be observed within 8-18 GHz, and the resonant frequency counts are inclined to be in direct proportion to the square-split-ring number over 8-18 GHz. Besides, the proposed sandwiched metamaterial with three square-split-ring resonators and three wires presents the widest frequency band of left-hand characteristics in a range of 8-18 GHz. Further, electromagnetic field distributions demonstrated that the induced magnetic dipole dominates the resonant absorption. The multi-peak resonance characteristics of square-split-ring resonant structure are considered to be a promising candidate for selective-frequency absorption or modulation toward microwave frequency band.展开更多
A new method based on the finite difference time domain(FDTD)method is presented to numerically analyze the transmission and reflection characteristic of composite materials with negative effective permittivity.The nu...A new method based on the finite difference time domain(FDTD)method is presented to numerically analyze the transmission and reflection characteristic of composite materials with negative effective permittivity.The numerical results are compared with the results of the existing theoretical model and the experimental data.The feasibility of analyzing the composite materials using the FDTD method is validated.It is useful for the design and application of the composite materials.展开更多
We have studied the self-consistent states of nano- and micro-particle polarized powders and structures consisting of parallel particle chains and have determined conditions under which the static dielectric permittiv...We have studied the self-consistent states of nano- and micro-particle polarized powders and structures consisting of parallel particle chains and have determined conditions under which the static dielectric permittivity of a disperse system is negative. It has been shown that in such system an electric current runs without ohmic losses. We present the arguments for the physics of spontaneous emergence of the electric field in disperse systems made up of electrically neutral particles. It has been determined the influence the phase boundaries of a disperse system has on the origin of spontaneous polarization state. The structures consisting of parallel chains of dielectric particles can exhibit spontaneous polarization. In this case the properties of the spherical structure are similar to those of the ball lightning. It has been established correspondence of the obtained theoretical results with the experimental data available in the literature.展开更多
Electromagnetic metamaterials have attracted widespread attention because of their unique properties,and the introduction of conductive metals or carbon into an insulating matrix is the main method for preparing metam...Electromagnetic metamaterials have attracted widespread attention because of their unique properties,and the introduction of conductive metals or carbon into an insulating matrix is the main method for preparing metamaterials.Silicon nitride ceramics have become an ideal matrix for electromagnetic metamaterials because of their high degree of insulation,high thermal conductivity,high-temperature resistance,corrosion resistance,and excellent mechanical properties.However,owing to poor sintering activity,chemical incompatibility,thermal expansion mismatch,or second-phase melt agglomeration,it is difficult to prepare dense silicon nitride-based metamaterials without a mechanical pressure-assisted sintering process,which greatly limits their high-performance preparation and industrial application.To address this issue,this work proposes the use of the high melting point metal tungsten as the conductive second phase.Through the control of chemical reactions,analysis,and regulation of the densification process,the materials were fully densified by gas pressure sintering.After the introduction of tungsten,not only did the electrical and thermal conductivity properties of the silicon nitride ceramics improve,but a negative permittivity behavior was also observed when the tungsten content reached 20 vol%.A new type of dense silicon nitride-based metamaterials with great industrial potential was proposed and prepared,which can guide the preparation and industrial application of high-performance metamaterials.展开更多
基金National Natural Science Foundation of China(No.52272117)National Key Research and Development Program of China(Nos.2022YFB3505104,2022YFB3706604)National Youth Fund(No.52207239).
文摘Composites featuring negative permittivity have garnered significant attention for their potential in novel capacitance designs,coil-less electrical inductors,and electromagnetic shielding applications.In this study,we prepared polyvinylidene fluoride(PVDF)matrix composites filled with ZrO_(2)/C nanoparticles de-rived from metal-organic frameworks(MOFs)via a hot-pressing method.With an increase in the ZrO_(2)/C content to 30 wt.%,electrical percolation was observed,accompanied by a transition mechanism from hopping conduction to metal-like conduction.This enabled the realization of ZrO_(2)/C/PVDF composites with tailorable negative permittivity properties,attributed to the plasmonic oscillation of free electrons in the composites beyond the percolation threshold(30 wt.%).Furthermore,the permittivity transition along to a shift in the electrical behavior of the percolative composites from capacitive to inductive.We explored the regulatory mechanism behind the negative permittivity in this random composite system,and our findings highlight the potential of these tunable negative permittivity media as promising candi-dates for diverse electromagnetic applications.
基金financially supported by the National Natural Science Foundation of China(Nos.52101178 and 52271182)the Natural Science Foundation of Shanghai(No.22ZR1426800)+3 种基金the Young Elite Scientist Sponsorship Program by China Association for Science and Technology(No.YESS20200257)Shanghai Pujiang Program(No.22PJ1411300)the Innovation Program of Shanghai Municipal Education Commission(No.2019-01-07-00-10-E00053)the Natural Science Foundation of Shandong Province(No.ZR2021QE090)。
文摘Flexible composites with negative permittivity have a very broad development prospect in flexible electronics and wearable devices.Currently,how to control the negative permittivity except for from their intrinsic properties of components is still a challenge.In this study,the negative permittivity and frequency dispersion were adjusted by changing the heat treatment temperature.Polyvinylidene fluoride(PVDF)was selected as the flexible matrix and reduced graphene oxide(rGO)as the functional filler to prepare rGO/PVDF membranous composites.The negative permittivity was observed in rGO/PVDF composites film,and the effect of heat treatment temperature on the negative permittivity was further studied.It indicated that a higher heat treatment temperature contributed to the formation of conductive network,so as to obtaining negative permittivity.When the molding temperature was 70℃,the negative permittivity spectrum conformed to the Drude model was only observed in the composites with 35 wt%content of rGO.After the heat treatment temperature reached 180℃,when the content of rGO decreased to 25 wt%,the composites film achieved negative permittivity(~-10),which had a low-frequency dispersion in the test frequency range.The negative permittivity of in composites can be regulated by adjusting the heat treatment temperature,which promotes the application and development of flexible metamaterials in underwater sensing and detection,etc.
基金supported by the National Natural Science Foundation of China(Nos.52106099 and 51576004)the Natural Science Foundation of Shandong Province(No.ZR2022YQ57)the Taishan Scholars Program.
文摘Phonon polaritons(PhPs)exhibit directional in-plane propagation and ultralow losses in van der Waals(vdW)crystals,offering new possibilities for controlling the flow of light at the nanoscale.However,these PhPs,including their directional propagation,are inherently determined by the anisotropic crystal structure of the host materials.Although in-plane anisotropic PhPs can be manipulated by twisting engineering,such as twisting individual vdW slabs,dynamically adjusting their propagation presents a significant challenge.The limited application of the twisted bilayer structure in bare films further restricts its usage.In this study,we present a technique in which anisotropic PhPs supported by bare biaxial vdW slabs can be actively tuned by modifying their local dielectric environment.Excitingly,we predict that the iso-frequency contour of PhPs can be reoriented to enable propagation along forbidden directions when the crystal is placed on a substrate with a moderate negative permittivity.Besides,we systematically investigate the impact of polaritonic coupling on near-field radiative heat transfer(NFRHT)between heterostructures integrated with different substrates that have negative permittivity.Our main findings reveal that through the analysis of dispersion contour and photon transmission coefficient,the excitation and reorientation of the fundamental mode facilitate increased photon tunneling,thereby enhancing heat transfer between heterostructures.Conversely,the annihilation of the fundamental mode hinders heat transfer.Furthermore,we find the enhancement or suppression of radiative energy transport depends on the relative magnitude of the slab thickness and the vacuum gap width.Finally,the effect of negative permittivity substrates on NFRHT along the[001]crystalline direction ofα-MoO3 is considered.The spectral band where the excited fundamental mode resulting from the negative permittivity substrates is shifted to the first Reststrahlen Band(RB 1)ofα-MoO_(3) and is widened,resulting in more significant enhancement of heat flux from RB 1.We anticipate our results will motivate new direction for dynamical tunability of the PhPs in photonic devices.
基金supported by the National Natural Science Foundation of China(Nos.51771104,51871146,51971119)the Future Plan for Young Talent of Shandong University(No.2016WLJH40)the Innovation Program of Shanghai Municipal Education Commission(No.2019-01-07-00-10-E00053)。
文摘Negative permittivity has been widely studied in various metamaterials and percolating composites, of which the anomalous dielectric behavior was attributed to critical structural properties of building blocks.Herein, mono-phase ceramics of indium tin oxides(ITO) were sintered for epsilon-negative materials in MHz-k Hz frequency regions. Electrical conductivity and complex permittivity were analyzed with DrudeLorentz oscillator model. Carriers’ characters were measured based on Hall effect and the magnitude and frequency dispersion of negative permittivity were mainly determined by carrier concentration.Temperature-dependent dielectric properties further proved the epsilon-negative behaviors were closely associated with free carriers’ collective responses. It’s found that negative permittivity of ITO ceramics was mainly caused by plasma oscillations of free carriers, while the dielectric loss was mainly attributed to conduction loss. Negative permittivity realized here was related to materials intrinsic nature and this work preliminarily determined the mechanism of negative permittivity in doped ceramics from the perspective of carriers.
基金supported by the National Natural Science Foundation of China(Nos.51771104,51871146,51971119)the Natural Science Foundation of Shandong Province(No.ZR2020YQ32)the Innovation Program of Shanghai Municipal Education Commission(No.2019-01-07-00-10-E00053)。
文摘The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is beneficial to reduce plasma frequency so that negative permittivity is achieved in kHz region.Negative permittivity achieved by percolating composites is restricted in practicality due to its instability nature at high temperatures.To achieve temperature-stable negative permittivity in kHz region,monophase La_(1-x)Ba_(x)CoO_(3)ceramics were prepared,and the transition from dielectric to metal was elaborated in the perspective of electrical conductivity and negative permittivity.The plasma-like negative permittivity is attained in kHz region,which is interpreted by the collective oscillation of low electron density.The temperature-stable negative permittivity is based on the fact that the plasmonic state will not be undermined at high temperatures.In addition,zero-crossing behavior of real permittivity is observed in La_(0.9)Ba_(0.1)CoO_(3)sample,which provides a promising alternative to designing epsilon-near-zero materials.This work makes the La_(1-x)Ba_(x)CoO_(3)system a source material for achieving effective negative permittivity.
基金sponsored by the National Natural Science Foundation of China (Grant No.51803119,51871146 and 51771108)the Innovation Program of Shanghai Municipal Education Commission (Grant No.2019-01-07-00-10-E00053)+1 种基金"Chenguang Program" supported by Shanghai Education Development Foundation and Shanghai Municipal Education Commission (Grant No.18CG56)the Science and Technology Commission of Shanghai Municipality (Grant No.18DZ1112902,No.18DZ1100802)
文摘Recently,increasing attention has been concentrated on negative permittivity with the development of the emerging metamaterials composed of periodic array structures.However,taking facile preparation into consideration,it is important to achieve negative permittivity behavior based on materials'intrinsic properties rather than their artificially periodic structures.In this paper,we proposed to fabricate the percolating composites with copper dispersed in epoxy(EP)resin by a polymerization method to realize the negative permittivity behavior.When Cu content in the composites reached to 80 wt%,the conductivity abruptly went up by three orders of magnitudes,suggesting a percolation behavior.Below the percolation threshold,the conductivity spectra conform to Jonscher's power law;when the Cu/EP composites reached to percolating state,the conductivity gradually reduced in high frequency region due to the skin effect.It is indicated that the conductive mechanism changed from hopping conduction to electron conduction.In addition,the permittivity did not increase monotonously with the increase of Cu content in the vicinity of percolation threshold,due to the presence of leakage current.Meanwhile,the negative permittivity conforming to Drude model was observed above the percolation threshold.Further investigation revealed that there was a constitutive relationship between the permittivity and the reactance.When conductive fillers are slightly above the percolation threshold,the inductive characteristic derived from conductive percolating network leads to the negative permittivity.Such epsilon-negative materials can potentially be applied in novel electrical devices,such as high-power microwave filters,stacked capacitors,negative capacitance field effect transistors and coil-free resonators.In addition,the design strategy based on percolating composites provides an approach to epsilon-negative materials.
基金financially supported by the National Natural Science Foundation of China (Nos.52101176,11604060,22005071 and 52101010)the China Postdoctoral Science Foundation (No.2020M671992)+3 种基金Guangdong Basic and Applied Basic Research Foundation (No.2021A1515110883)Guizhou Provincial Science and Technology Projects (No.ZK[2022]General044)the Cultivation Programs Research Foundation of Guizhou University (No.2019-64)support of the Fund of Natural Science Special (Special Post)Research Foundation of Guizhou University[Grant No.2023-032]。
文摘Metacomposites with negative permittivity usually possess huge dielectric loss,showing potential for micro-wave attenuation devices where huge heat would generate.Herein,carbon nanotube-carbon black/CaCu_(3-)Ti_(4)O_(12)(CNT-CB/CCTO)ternary metacomposites were fabricated by spark plasma sintering.The CNT-CB dualphase filler was pre-pared through electrostatic selfassembly process in order to construct an effective 3-dimensional(3D)carbon network in CCTO matrix.The percolation threshold of CNT-CB/CCTO composites was identified at filler content of 12.52 wt%which accompanied with an essential change of conduction mechanism.The negative permittivity was derived from low-frequency plasmonic state of the 3D carbon network,described by Drude model.The problem of heat transport,generally occurring in negative permittivity materials,has been solved and optimized in obtained ternary metacomposites beneftting from the substantially high thermal conductivity(9.49-2.00 W·m^(-1)·K^(-1))and diffusivity(2.74-1.22mm^(2)·s^(-1)).This work could spark significant development of practical application of metacomposites on novel electronic devices and electromagnetic apparatus.
基金Project supported by the State Key Development Program for Basic Research of China （Grant No 2004CB719800）, partially by the National Natural Science Foundation of China （Grant No 10604046） and the Chinese Doctoral Science Foundation.
文摘A new quantum optical mechanism to realize simultaneously negative electric permittivity and magnetic permeability is suggested. In order to obtain a negative permeability, we choose a proper atomic configuration that can dramatically enhance the contribution of the magnetic-dipole allowed transition via the atomic phase coherence. It is shown that the atomic system chosen with proper optical parameters can give rise to striking electromagnetic responses （leading to a negative refractive index） and that the atomic vapour becomes a left-handed medium in an optical frequency band. Differing from the previous schemes of artificial composite metamaterials （based on classical electromagnetic theory） to achieve the left-handed materials, which consist of anisotropic millimetre-scale composite structure units, the left-handed atomic vapour presented here is isotropic and homogeneous at the atomic-scale level. Such an advantage may be valuable in realizing the superlens （and hence perfect image） with left-handed atomic vapour.
基金This work was financially supported by the National Natural Science Foundation of China(No.52205593)the Fund of Natural Science Special(Special Post)Research Foundation of Guizhou University(No.2023-032)the Platform of Science and Technology and Talent Team Plan of Guizhou Province(No.GCC[2023]007).
文摘CaCu_(3)Ti_(4)O_(12)(CCTO)ceramic nanocomposites incorporating graphene–carbon black(GRCB)fillers were fabricated by spark plasma sintering process.The percolative effects of conductive GRCB fillers on dielectric response of GRCB/CCTO ternary metacomposites were systematically investigated.The weakly real permittivity(ε′)-negative response(ε′~−1×10^(2))was achieved which originated from weakly low-frequency plasmonic state of free carriers within constructed GRCB networks.With enhancing three-dimensional GRCB network,the plasma frequency of metacomposites increased while the damping factor decreased.Herein,theε′-negative values of metacomposites were tuned from−10^(2) to−10^(4) orders of magnitude andε′-near-zero(ENZ)frequencies from~142 to~340 MHz which substantially benefited from the moderate carrier concentration of GRCB dual fillers.The Drude model and equivalent circuit models were adopted to demonstrate dielectric and electrical characteristics.The obtained metacomposites show strong EM shielding effect along with enhanced plasmonic oscillation and even better achieving perfect EM shielding effect in ENZ media.This work achieves the tunableε′-negative andε′-near-zero response and more importantly clarifies its regulation mechanism in ceramic-based ternary metacomposites,which opens up the possibility of designing high-performance EM shielding materials based on metacomposites.
基金Supported by the National Natural Science Foundation of China under Grant No 51102007the Fund for Discipline Construction of Beijing University of Chemical Technology under Grant No XK1702
文摘The anti-resonant phenomenon of effective electromagnetic parameters of metamaterials has aroused controversy due to negative imaginary permittivity or permeability. It is experimentally found that the negative imaginary permittivity can occur for the natural passive materials near the Fabry Perot resonances. We reveal the nature of negative imaginary permittivity, which is correlated with the magnetoelectric coupling. The anti-resonance of permittivity is a non-inherent feature for passive materials, while it can be inherent for devices or metamaterials. Our finding validates that the negative imaginary part of effective permittivity does not contradict the second law of thermodynamics for metamaterials owing to the magnetoelectric coupling.
基金supported by the National Key Basic Research Special Foundation of China (Grant No 2006CB921701)the National Natural Science Foundation of China (Grant Nos 10474072,10634050 and 50477048) the Shanghai Science and Technology Committee of China (Grant No 07DZ22302)
文摘We take a finite dielectric photonic crystal as a homogeneous slab and have extracted the effective parameters. Our systematic study shows that the effective permittivity or permeability of dielectric photonic crystal is negative within a band gap region. This means that the band gap might act as ε-negative materials （ENMs） with ε 〈 0 and μ 〉 0, or μ-negative materials （MNMs） with ε 〉 0 and μ 〈 0. Moreover the effective parameters sensitively rely on size, surface termination, symmetry, etc. The effective parameters can be used to design full transmission tunnelling modes and amplify evanescent wave. Several cases are studied and the results show that dielectric photonic band gap can indeed mimic a single negative material （ENM or MNM） under some restrictions.
基金supported by the Research Starting Foundation of Shaanxi University of Science and Technology(Program No.2019QNBJ-01)the Research Foundation for Thousand Young Talent Plan of Shaanxi province of China。
文摘NiFe_(2)O_(4)/polypyrrole(NiFe_(2)O_(4)/PPy)nanocomposites are prepared by a simple surface-initiated polymerization method and demonstrate negative permittivity in the low frequency regions.These nanocomposites also exhibit significantly enhanced electromagnetic wave(EMW)absorption property in the high frequency regions.Compared with pure PPy,the enhanced negative permittivity is observed in the NiFe_(2)O_(4)/PPy nanocomposites with a NiFe_(2)O_(4)loading of 5.0,10.0,20.0 and 40.0 wt%,indicating the formation of metal-like electrical conducting network in NiFe_(2)O_(4)/PPy nanocomposites.Moreover,the negative permittivity could be tuned by changing the NiFe_(2)O_(4)loading.The minimum reflection loss(RL)of-40.8 dB is observed in the 40.0 wt%NiFe_(2)O_(4)/PPy composites with a thickness of only 1.9 mm.The effective absorption bandwidth below-10.0 and-20.0 dB reaches 6.08 and 2.08 GHz,respectively.The enhanced EMW absorption performance benefits from the improved independence matching,EMW attenuation capacity,and synergistic effects of conduction loss,dielectric loss(interfacial and dipole polarizations)and magnetic loss(exchange and natural resonances).This research work provides a guidance for the fabrication of nanocomposites with an excellent EMW absorption.
基金This work was financially supported by the National Natural Science Foundation of China(No.52073075)the Shenzhen Science and Technology Program(No.KQTD20170809110344233)the Initial Scientific Research Foundation of Overseas High-level Talents of Harbin Institute of Technology(Shenzhen)(No.DB11409008).
文摘Facing the challenges posed by exponentially increasing e-waste,the development of recyclable and tran-sient electronics has paved the way to an environmentally-friendly progression strategy,where electron-ics can disintegrate and/or degrade into eco-friendly end products in a controlled way.Natural polymers possess cost and energy efficiency,easy modification,and fast degradation,all of which are ideal prop-erties for transient electronics.Gelatin is especially attractive due to its unique thermoreversible gelation processes,yet its huge potential as a multifunctional electronic material has not been well-researched due to its limited mechanical strength and low conductivity.Herein,we explored versatile applications of gelatin-based hydrogels through the assistance of multifunctional additives like carbon nanotubes to enhance their electromechanical performances.The optimized gelatin hydrogel displays not only a high conductivity of 0.93 S/m,electromagnetic shielding effectiveness of 39.6 dB,and tensile stress tolerance of 263 kPa,but also shows a negative permittivity phenomenon,which may find versatile applications in novel electronics.As a proof of concept,hydrogels were assembled as wearable sensors to sensitively de-tect static and dynamic pressures and strains generated by solids,liquids,and airflow,as well as diverse body movements.Furthermore,the recyclability,biocompatibility,and degradability of gelatin-based hy-drogels were well studied and analyzed.This work outlines a facile method to design multifunctional transient materials for wearable,sustainable,and eco-friendly electronics.
基金supported by the Ministry of Science and Technology of China through 973-project under Grant(2015CB654601)National Nature Science Foundation of China(51902167)+1 种基金Fund in Ningbo UniversityKey Laboratory of Engineering Dielectrics and Its Application(Harbin University of Science and Technology),Ministry of Education.
文摘Percolating composites with negative permittivity can be promising candidates for metamaterials.Herein,novel all-organic composite films containing of random coil polypyrrole(PPy)and poly(-vinylidene fluoride)(PVDF)are fabricated via a solution casting method.The random coil PPy is prepared by oxidative template assembly approach for the first time.The experimental result indicates that the negative permittivity is easily adjusted through controlling the random coil PPy contents.Especially,the random coil PPy contents exceeded 7 wt% the negative permittivity appear attributed to the formation of 3D interconnected PPy network.This facile approach not only opens a new way to preparing negative permittivity of all-organic composite films,but also points out a route to facilitate the practical applications of metamaterials.
基金the financial supports from the National Natural Science Foundation of China(51871146)the Natural Science Foundation of Shanghai(22ZR1426800)+3 种基金Young Elite Scientist Sponsorship Program by China Association for Science and Technology(YESS20200257)the Innovation Program of Shanghai Municipal Education Commission(2019-01-07-0010-E00053)China National Postdoctoral Program for Innovative Talents(BX2021174)China Postdoctoral Science Foundation(2021M692033)。
文摘Epsilon-near-zero(ENZ)material has been a research hotspot in recent years due to unique physical properties such as inverse Doppler effect and negative refractive index,showing great potentials in the fields of flexible electronics,wearable devices,sensors,etc.The ENZ materials are mostly reported at visible,infrared and terahertz wavelengths,while the report about ENZ materials at radio frequency is rare.In this work,flexible and biocompatible poly(vinyl alcohol)/multi-walled carbon nanotubes(PVA/MWCNTs)hydrogels,which were successfully fabricated by an environmentally friendly method,were used as ENZ materials at radio frequency for the first time.Cytotoxicity experiments proved that the experimental process and products are green,environmentally friendly and biocompatible.The microstructure,crystalline structure,chemical composition and dielectric properties were investigated.Two different water states,which were free water molecules and bound water molecules,coexisted in these PVA/MWCNTs hydrogels and accounted for about 37.5 wt%and 15.9 wt%respectively by analyzing the thermogravimetric analysis curves.When the MWCNTs content reached 12 wt%and 15 wt%,the continuous conductive MWCNTs network was formed in the hydrogel,and ENZ phenomenon was observed at about 760 k Hz and 580 k Hz respectively,which was attributed to the interband transition.Considering the flexibility and non-toxicity of PVA/MWCNTs hydrogels,the ENZ properties of this structure at the radio frequency can be well used in wearable invisibility cloak,flexible electronics,skin sensors and other wearable devices.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60768001 and 10464002)
文摘In this paper we have investigated three external fields interacting with the four-level Y-type atomic system described by the density-matrix approach. The results show that left-handedness with zero absorption is achieved. The zero absorption property displays the possibility of manipulation by varying the phase and the intensity of the coupling field. Also, the zero absorption property may be used to amplify the evanescent waves that have been lost in imaging by traditional lenses. We propose an approach to obtain a negative refractive medium with zero absorption and the possibility of enhaneeingthe imaging resolution in realizing ＇superlenses＇.
基金Project(2017YFA0204600)supported by the National Key Research and Development Program of ChinaProject(51802352)supported by the National Natural Science Foundation of ChinaProject(2019JJ50768)supported by the Natural Science Foundation of Hunan Province of China。
文摘Left-hand materials have drawn increasing attention from many disciplines and found widespread application, especially in microwave engineering. A sandwiched metamaterial consisting of multi-nested square-split-ring resonators on the top side and a set of wires on the back side is proposed. Scattering parameters are retrieved by high-frequency structure simulator(HFSS) software based on the finite element method. Effects of square-split-ring number on the left-hand characteristics containing negative values of permittivity, permeability, and refractive index have been intensively investigated. Simulated results show that obvious resonant left-hand characteristics could be observed within 8-18 GHz, and the resonant frequency counts are inclined to be in direct proportion to the square-split-ring number over 8-18 GHz. Besides, the proposed sandwiched metamaterial with three square-split-ring resonators and three wires presents the widest frequency band of left-hand characteristics in a range of 8-18 GHz. Further, electromagnetic field distributions demonstrated that the induced magnetic dipole dominates the resonant absorption. The multi-peak resonance characteristics of square-split-ring resonant structure are considered to be a promising candidate for selective-frequency absorption or modulation toward microwave frequency band.
基金supported by the National Natural Science Foundation of China(Grant No.60271018).
文摘A new method based on the finite difference time domain(FDTD)method is presented to numerically analyze the transmission and reflection characteristic of composite materials with negative effective permittivity.The numerical results are compared with the results of the existing theoretical model and the experimental data.The feasibility of analyzing the composite materials using the FDTD method is validated.It is useful for the design and application of the composite materials.
文摘We have studied the self-consistent states of nano- and micro-particle polarized powders and structures consisting of parallel particle chains and have determined conditions under which the static dielectric permittivity of a disperse system is negative. It has been shown that in such system an electric current runs without ohmic losses. We present the arguments for the physics of spontaneous emergence of the electric field in disperse systems made up of electrically neutral particles. It has been determined the influence the phase boundaries of a disperse system has on the origin of spontaneous polarization state. The structures consisting of parallel chains of dielectric particles can exhibit spontaneous polarization. In this case the properties of the spherical structure are similar to those of the ball lightning. It has been established correspondence of the obtained theoretical results with the experimental data available in the literature.
基金supported by the National Natural Science Foundation of China(No.52102080)the Youth Science Foundations of Gansu Province(No.23JRRA598)the Shandong Provincial Natural Science Foundation(Nos.ZR2020ZD29 and ZR2021JQ20).
文摘Electromagnetic metamaterials have attracted widespread attention because of their unique properties,and the introduction of conductive metals or carbon into an insulating matrix is the main method for preparing metamaterials.Silicon nitride ceramics have become an ideal matrix for electromagnetic metamaterials because of their high degree of insulation,high thermal conductivity,high-temperature resistance,corrosion resistance,and excellent mechanical properties.However,owing to poor sintering activity,chemical incompatibility,thermal expansion mismatch,or second-phase melt agglomeration,it is difficult to prepare dense silicon nitride-based metamaterials without a mechanical pressure-assisted sintering process,which greatly limits their high-performance preparation and industrial application.To address this issue,this work proposes the use of the high melting point metal tungsten as the conductive second phase.Through the control of chemical reactions,analysis,and regulation of the densification process,the materials were fully densified by gas pressure sintering.After the introduction of tungsten,not only did the electrical and thermal conductivity properties of the silicon nitride ceramics improve,but a negative permittivity behavior was also observed when the tungsten content reached 20 vol%.A new type of dense silicon nitride-based metamaterials with great industrial potential was proposed and prepared,which can guide the preparation and industrial application of high-performance metamaterials.
