Complex-amplitude holographic metasurfaces(CAHMs)with the flexibility in modulating phase and amplitude profiles have been used to manipulate the propagation of wavefront with an unprecedented level,leading to higher ...Complex-amplitude holographic metasurfaces(CAHMs)with the flexibility in modulating phase and amplitude profiles have been used to manipulate the propagation of wavefront with an unprecedented level,leading to higher image-reconstruction quality compared with their natural counterparts.However,prevailing design methods of CAHMs are based on Huygens-Fresnel theory,meta-atom optimization,numerical simulation and experimental verification,which results in a consumption of computing resources.Here,we applied residual encoder-decoder convolutional neural network to directly map the electric field distributions and input images for monolithic metasurface design.A pretrained network is firstly trained by the electric field distributions calculated by diffraction theory,which is subsequently migrated as transfer learning framework to map the simulated electric field distributions and input images.The training results show that the normalized mean pixel error is about 3%on dataset.As verification,the metasurface prototypes are fabricated,simulated and measured.The reconstructed electric field of reverse-engineered metasurface exhibits high similarity to the target electric field,which demonstrates the effectiveness of our design.Encouragingly,this work provides a monolithic field-to-pattern design method for CAHMs,which paves a new route for the direct reconstruction of metasurfaces.展开更多
Polarization is one of the basic characteristics of electromagnetic(EM)waves,and its flexible control is very important in many practical applications.At present,most of the multifunction polarization metasurfaces are...Polarization is one of the basic characteristics of electromagnetic(EM)waves,and its flexible control is very important in many practical applications.At present,most of the multifunction polarization metasurfaces are electrically tunable based on PIN and varactor diodes,which are easy to operate and have strong real-time performance.However,there are still some problems in them,such as few degrees of freedom of planar structure control,complex circuit,bulky sample,and high cost.In view of these shortcomings,this paper proposes a Miura origami based reconfigurable polarization conversion metasurface for multifunctional control of EM waves.The interaction between the electric dipoles is changed by adjusting the folding angleθ,thereby tuning the operating frequency of the polarization conversion and the polarization state of the reflected wave.This mechanical control method brings more degrees of freedom to manipulate EM waves.And the processed sample is with lightweight and low cost.To verify the performance of the proposed origami polarization converter,a Miura origami structure loaded with metal split rings is designed and fabricated.The operating frequency of the structure can be tuned in different folding states.In addition,by controlling the folding angleθ,linear-to-linear and linear-to-circular polarization converters can be realized at different folding states.The proposed Miura origami polarization conversion metasurface provides a new idea for reconfigurable linear polarization conversion and multifunctional devices.展开更多
In this work,a quadruple-band dielectric metamaterial absorber(MMA)was proposed and studied,which is composed of eight cuboid dielectric particles and a metallic ground plate.When electromagnetic wave is incident on t...In this work,a quadruple-band dielectric metamaterial absorber(MMA)was proposed and studied,which is composed of eight cuboid dielectric particles and a metallic ground plate.When electromagnetic wave is incident on the dielectric particles,dielectric particles act as resonators and produce abundant resonant modes,which can result in perfect absorption.In simulation,four absorption peaks are observed at 9.13,9.62,10.0 and 10.46 GHz with 88%,89%,100%and 96%,respectively.By adjusting geometry parameters of the dielectric particles,dielectric MMAs with different bands can be obtained.Further investigation shows that the absorption peaks can be changed by increasing the permittivity of the dielectric.Based on the designing technique of using simple cuboid dielectric particles directly acting as resonator,this work provides a simple method to construct multiband alldielectric MMA.展开更多
Frequency selective surface(FSS)has been extensively studied due to its potential applications in radomes,antenna reflectors,high-impedance surfaces and absorbers.Recently,a new principle of designing FSS has been pro...Frequency selective surface(FSS)has been extensively studied due to its potential applications in radomes,antenna reflectors,high-impedance surfaces and absorbers.Recently,a new principle of designing FSS has been proposed and mainly studied in two levels.In the level of materials,dielectric materials instead of metallic patterns are capable of achieving more functional performance in FSS design.Moreover,FSSs made of dielectric materials can be used in different extreme environments,depending on their electrical,thermal or mechanical properties.In the level of design principle,the theory of metamaterial can be used to design FSS in a convenient and concise way.In this review paper,we provide a brief summary about the recent progress in all-dielectric metamaterial frequency selective surface(ADM-FSS).The basic principle of designing ADM-FSS is summarized.As significant tools,Mie theory and dielectric resonator(DR)theory are given which illustrate clearly how they are used in the FSS design.Then,several design cases including dielectric particle-based ADM-FSS and dielectric network-based ADM-FSS are introduced and reviewed.After a discussion of these two types of ADM-FSSs,we reviewed the existing fabrication techniques that are used in building the experiment samples.Finally,issues and challenges regarding the rapid fabrication techniques and further development aspects are discussed.展开更多
In this paper,we demonstrate a method of designing all-dielectric metamaterial frequency selective surface(FSS)with ceramic resonators in spatial arrangement.Compared with the traditional way,spatial arrangement provi...In this paper,we demonstrate a method of designing all-dielectric metamaterial frequency selective surface(FSS)with ceramic resonators in spatial arrangement.Compared with the traditional way,spatial arrangement provides a flexible way to handle the permutation and combination of different ceramic resonators.With this method,the resonance response can be adjusted easily to achieve pass/stop band effects.As an example,a stop band spatial arrangement all-dielectric metamaterial FSS is designed.Its working band is in 11.65–12.23 GHz.By adjusting permittivity and geometrical parameters of ceramic resonators,we can easily modulate the resonances,band pass or band stop characteristic,as well as the working band.展开更多
Reciprocity is ubiquitous in antennas for receiving and radiating electromagnetic(EM) waves, i.e., if an antenna has good receiving performance at a given direction, it also has good radiation performance in that dire...Reciprocity is ubiquitous in antennas for receiving and radiating electromagnetic(EM) waves, i.e., if an antenna has good receiving performance at a given direction, it also has good radiation performance in that direction.Inspired by this, we propose a method of designing a quasi-ominibearing retro-reflective metagrating(RRMG)protected by the reciprocity of antennas. Based on the second-order mode around 15.0 GHz of a short-circuited structured patch antenna(SPA), incident transverse magnetic waves can be received, channeled into the coaxial lines, reflected by the shortened end, and finally re-radiated into free space with a reversed wave vector. RRMGs are contrived consisting of this identical SPA, with a grating constant allowing ±2nd-, ±1st-, and zeroth-order diffractions. Oblique incidence, plus the tilted nulls of the re-radiation pattern, can eliminate -1st, zeroth,+1st, and +2nd orders, and only the -2nd order is left to achieve retro-reflections. Prototypes were fabricated and measured. Simulated and measured results show that the RRMGs maintain only -2nd-order diffraction for incident angles 32.2° ≤ θ_(i)< 90.0° in four quadrants, and that RRMGs can achieve quasi-omnibearing retro-reflections for θ_(i)= 50.0°. The use of higher-order diffraction brings more degrees of freedom in manipulating EM waves, and this strategy can be readily extended to millimeter waves, THz wave, or even optical regimes.展开更多
In this paper,we propose a novel transmit/reflect switchable frequency selective surface(FSS)in millimeter wave band based on the effective medium theory under quasi-static limit,which is designed with square-hole ele...In this paper,we propose a novel transmit/reflect switchable frequency selective surface(FSS)in millimeter wave band based on the effective medium theory under quasi-static limit,which is designed with square-hole elements cut from continuum dielectric plates.The building elements of the surface are composed of all dielectric metamaterial rather than metal material.With proper structural design and parameters tuning,the resonance frequencies can be tuned appropriately.The frequency response of the surface can be switched from that of a reflecting structure to a transmitting one by rotating the surface 90°,which means under different incident polarizations.The reflective response can be realized due to the effect of electric and magnetic resonances.Theoretical analysis shows that the reflective response arises from impedance mismatching by electric and magnetic resonances.And the transmitting response is the left-handed passband,arises from the coupling of the electric and magnetic resonances.In addition,effective electromagnetic parameters and the dynamic induced field distributions are analyzed to explain the mechanism of the responses.The method can also be used to design switchable all-dielectric FSS with continuum structures in other frequencies.展开更多
Metasurfaces have provided an unprecedented degree of freedom(DOF)in the manipulation of electromagnetic waves.A geometric phase can be readily obtained by rotating the meta-atoms of a metasurface.Nevertheless,such ge...Metasurfaces have provided an unprecedented degree of freedom(DOF)in the manipulation of electromagnetic waves.A geometric phase can be readily obtained by rotating the meta-atoms of a metasurface.Nevertheless,such geometric phases are usually spin-coupled,with the same magnitude but opposite signs for left-and right-handed circularly polarized(LCP and RCP)waves.To achieve independent control of LCP and RCP waves,it is crucial to obtain spin-decoupled geometric phases.In this paper,we propose to obtain completely spin-decoupled geometric phases by engineering the surface current paths on meta-atoms.Based on the rotational Doppler effect,the rotation manner is first analyzed,and it is found that the generation of a geometric phase lies in the rotation of the surface current paths on meta-atoms.Since the induced surface current paths under the LCP and RCP waves always start oppositely and are mirror-symmetrical with each other,it is natural that the geometric phases have the same magnitude and opposite signs when the meta-atoms are rotated.To obtain spin-decoupled geometric phases,the induced surface current under one spin should be rotated by one angle while the current under the other spin is rotated by a different angles.In this way,LCP and RCP waves can acquire different geometric phase changes.Proof-of-principle prototypes were designed,fabricated,and measured.Both the simulation and experiment results verify spin-decoupled geometric phases.This work provides a robust means to obtain a spindependent geometric phase and can be readily extended to higher frequency bands such as the terahertz,IR,and optical regimes.展开更多
Chiral mirrors can produce spin selective absorption for left-handed circularly polarized(LCP) or right-handed circularly polarized(RCP) waves. However, the previously proposed chiral mirror only absorbs the designate...Chiral mirrors can produce spin selective absorption for left-handed circularly polarized(LCP) or right-handed circularly polarized(RCP) waves. However, the previously proposed chiral mirror only absorbs the designated circularly polarized(CP) wave in the microwave frequency band, lacking versatility in practical applications.Here, we propose a switchable chiral mirror based on a pair of PIN diodes. The switchable chiral mirror has four working states, switching from the handedness-preserving mirror to the LCP mirror, RCP mirror, and perfect absorber. The basis of these advances is to change the chirality of two-dimensional(2D) chiral metamaterials and the circular conversion dichroism related to it, which is the first report in the microwave frequency band.Surface current distributions shed light on how switchable chiral mirrors work by handedness-selective excitation of reflective and absorbing electric dipole modes. Energy loss distributions verify the working mechanism. The thickness of the switchable chiral mirror is one-tenth of the working wavelength, which is suitable for integrated manufacturing. The measurement results are in good agreement with the simulation results.展开更多
Metasurfaces have provided unprecedented degrees of freedom in manipulating electromagnetic waves upon interfaces.In this work,we first explore the condition of wide operating bandwidth in the view of reflective schem...Metasurfaces have provided unprecedented degrees of freedom in manipulating electromagnetic waves upon interfaces.In this work,we first explore the condition of wide operating bandwidth in the view of reflective scheme,which indicates the necessity of anomalous dispersion.To this end,the leaky cavity modes(LCMs)in the metaatom are analyzed and can make effective permittivity inversely proportional to frequency.Here we employ the longitudinal Fabry-Perot(F-P)resonances and transverse plasmonic resonances to improve the LCMs efficiency.It is shown that the order of F-P resonance can be customized by the plasmonic modes,that is,the F-P cavity propagation phase should match the phase delay of surface currents excited on the meta-atom.The nth order F-P resonance will multiply the permittivity by a factor of n,allowing larger phase accumulation with increasing frequencies and forming nonlinear phase distribution which can be applied in weak chromatic-aberration focusing design.As a proof-of-concept,we demonstrate a planar weak chromatic-aberration focusing reflector with a thickness ofλ_(0)∕9 at 16.0-21.0 GHz.This work paves a robust way to advanced functional materials with anomalous dispersion and can be extended to higher frequencies such as terahertz,infrared,and optical frequencies.展开更多
Metasurfaces have intrigued long-standing research interests and developed multitudinous compelling applications owing to their unprecedented capability for manipulating electromagnetic waves,and the emerging programm...Metasurfaces have intrigued long-standing research interests and developed multitudinous compelling applications owing to their unprecedented capability for manipulating electromagnetic waves,and the emerging programmable coding metasurfaces(PCMs)provide a real-time reconfigurable platform to dynamically implement customized functions.Nevertheless,most existing PCMs can only act on the single polarization state or perform in the limited polarization channel,which immensely restricts their practical application in multitask intelligent metadevices.Herein,an appealing strategy of the PCM is proposed to realize tunable functions in co-polarized reflection channels of orthogonal circularly polarized waves and in co-polarized and cross-polarized reflection channels of orthogonal linearly polarized waves from 9.0 to 10.5 GHz.In the above six channels,the spindecoupled programmable meta-atom can achieve high-efficiency reflection and 1-bit digital phase modulation by selecting the specific ON/OFF states of two diodes,and the phase coding sequence of the PCM is dynamically regulated by the field-programmable gate array to generate the desired function.A proof-of-concept prototype is constructed to verify the feasibility of our methodology,and numerous simulation and experimental results are in excellent agreement with the theoretical predictions.This inspiring design opens a new avenue for constructing intelligent metasurfaces with higher serviceability and flexibility,and has tremendous application potential in communication,sensing,and other multifunctional smart metadevices.展开更多
Metasurface has provided unprecedented freedoms in manipulating electromagnetic(EM) waves, exhibiting fascinating functions. Conventionally, these functions are implemented right on metasurfaces, where spatial modulat...Metasurface has provided unprecedented freedoms in manipulating electromagnetic(EM) waves, exhibiting fascinating functions. Conventionally, these functions are implemented right on metasurfaces, where spatial modulations on EM wave amplitudes or phases are achieved by meta-atoms. This study proposes the concept of virtual metasurface(VM), which is formed by arrays of foci away from the entity metasurface. Unlike conventional metasurfaces, spatial modulations on the amplitudes or phases of EM waves occur in the air, with a focal length distance from the entity metasurface. As a proof of concept, we demonstrated a transmissive VM. The entity metasurface consists of transmissive focusing metasurface tiles(TFMTs) with the same focal length. Two TFMTs were designed with phase difference π to enable the most typical checkerboard configuration. The TFMTs were assembled to form the entity metasurface, whereas their foci formed the VM. Due to the π phase difference among adjacent foci, EM propagation along the normal direction was cancelled, leading to four tilted far-field beams. The concept of VM can be readily extended to higher frequencies from terahertz to optical regimes and may find wide applications in communication, camouflage, and other fields.展开更多
Three-dimensional chiral materials with intrinsic chirality play a crucial role in achieving a strong chiral response and flexible light manipulation.Reconfigurable chirality through the 3D morphological transformatio...Three-dimensional chiral materials with intrinsic chirality play a crucial role in achieving a strong chiral response and flexible light manipulation.Reconfigurable chirality through the 3D morphological transformation of chiral materials is significant for greater freedom in tailoring light but remains a challenge.Inspired by the unique 3D morphological memory capability of shape memory alloys(SMAs),we demonstrate and discuss a chiral resonator in the microwave regime that can realize reconfigurable chirality through 3D morphological transformation.The introduction of heating film realizes voltage control of SMA’s morphology for utilizing the temperature sensitivity of SMA better,enabling arbitrary control of circular dichroism(CD)flip and CD intensity.The qualitative and quantitative analysis of the surface current distribution of chiral enantiomers reveals that the chirality of metaatoms originates from the surge of electric dipole pxand electric quadrupole Q.It is worth mentioning that the proposed strategy to achieve reconfigurable chirality using 3D morphological transformations can be directly extended to other higher frequencies,such as visible,infrared,and terahertz bands.Significantly,our paradigm to study the relationship between complex 3D morphology and chirality holds potential for application in biosensing,spin detection,and spin-selective devices.展开更多
For camouflage applications,the performance requirements for metamaterials in different electromagnetic spectra are usually contradictory,which makes it difficult to develop satisfactory design schemes with multispect...For camouflage applications,the performance requirements for metamaterials in different electromagnetic spectra are usually contradictory,which makes it difficult to develop satisfactory design schemes with multispectral compatibility.Fortunately,empowered by machine learning,metamaterial design is no longer limited to directly solving Maxwell’s equations.The design schemes and experiences of metamaterials can be analyzed,summarized,and learned by computers,which will significantly improve the design efficiency for the sake of practical engineer-ing applications.Here,we resort to the machine learning to solve the multispectral compatibility problem of metamaterials and demonstrate the design of a new metafilm with multiple mechanisms that can realize small microwave scattering,low infrared emissivity,and visible transparency simultaneously using a multilayer back-propagation neural network.The rapid evolution of structural design is realized by establishing a mapping between spectral curves and structural parameters.By training the network with different materials,the designed network is more adaptable.Through simulations and experimental verifications,the designed architecture has good accuracy and robustness.This paper provides a facile method for fast designs of multispectral metafilms that can find wide applications in satellite solar panels,aircraft windows,and others.展开更多
Recently, we have witnessed an extraordinary spurt in attention toward manipulating electromagnetic waves by metasurfaces. Particularly, tailoring of circular polarization has attracted great amounts of interest in bo...Recently, we have witnessed an extraordinary spurt in attention toward manipulating electromagnetic waves by metasurfaces. Particularly, tailoring of circular polarization has attracted great amounts of interest in both microwave and optics regimes. Circular dichroism, an exotic chiroptical effect of natural molecules, has aroused discussion about this issue, yet it is still in its infancy. Herein, we initiate circular dichroism followed by controlling spin-selective wavefronts via chiral metasurfaces. An N-shaped chiral resonator loaded with two lumped resistors is proposed as the meta-atom producing an adequate phase gradient. Assisted by the ohmic dissipation of the introduced resistors, the effect of differential absorption provides an auxiliary degree of freedom for developing circularly polarized waves with a designated spin state. A planar corner reflector that can achieve retro-reflection and absorption for right-and left-handed circularly polarized incidence is theoretically simulated and experimentally observed at microwave frequency. Thus, our effort provides an alternative approach to tailoring electromagnetic waves in a circular dichroitic manner and may also find applications in multi-functional systems in optics and microwave regimes.展开更多
The power of controlling objects with mind has captivated a popular fascination to human beings.One possible path is to employ brain signal collecting technologies together with emerging programmable metasurfaces(PM),...The power of controlling objects with mind has captivated a popular fascination to human beings.One possible path is to employ brain signal collecting technologies together with emerging programmable metasurfaces(PM),whose functions or operating modes can be switched or customized via on-site programming or pre-defined software.Nevertheless,most of existing PMs are wire-connected to users,manually-controlled and not real-time.Here,we propose the concept of remotely mind-controlled metasurface(RMCM)via brainwaves.Rather than DC voltage from power supply or AC voltages from signal generators,the metasurface is controlled by brainwaves collected in real time and transmitted wirelessly from the user.As an example,we demonstrated a RMCM whose scattering pattern can be altered dynamically according to the user’s brain waves via Bluetooth.The attention intensity information is extracted as the control signal and a mapping between attention intensity and scattering pattern of the metasurface is established.With such a framework,we experimentally demonstrated and verified a prototype of such metasurface system which can be remotely controlled by the user to modify its scattering pattern.This work paves a new way to intelligent metasurfaces and may find applications in health monitoring,5G/6G communications,smart sensors,etc.展开更多
Chirality, as one of the ubiquitous properties in nature, has aroused striking attention in the fields of physics and materials sciences. For tailoring of light with more degree of freedom, circular dichroism has been...Chirality, as one of the ubiquitous properties in nature, has aroused striking attention in the fields of physics and materials sciences. For tailoring of light with more degree of freedom, circular dichroism has been considered as the auxiliary dimension to improving such an issue. Inspired by the Born-Kuhn plasmonic oscillation model, we demonstrate and discuss a chiral resonator to reveal reverse circular dichroism within two separate frequency bands in the microwave regime. The underlying physical mechanisms of bonding and anti-bounding modes are analyzed via transmission/reflection spectra and surface current distributions for different chiral enantiomers. To leverage the proposed paradigm to the application levels, especially for metaholography, we conduct the numerical simulation and experimental demonstration of two proofs of principles. Based on the Pancharatnam-Berry phase/amplitude modulation and complex-amplitude manipulation, respectively, the meta-holograms with independent targets of reconstructing images in full-space and reflected regions are achieved. Significantly, our paradigm may promise further applications in spin-controlled meta-devices for image processing, information encryption, anti-counterfeiting,remote sensing, and radar systems.展开更多
In this work,an optical transparent infrared high absorption metamaterial absorber is proposed based on indium tin oxide(ITO)substrate.Due to the fact that ITO holds high reflectivity property in infrared region while...In this work,an optical transparent infrared high absorption metamaterial absorber is proposed based on indium tin oxide(ITO)substrate.Due to the fact that ITO holds high reflectivity property in infrared region while transparent in optical region,ITO can be used in the application of Surface Plasmon Polaritons.In this design,three kinds of infrared metamaterial absorbers were proposed.All of them can achieve high absorption at 10.6μm while remaining transparent in visible region.LC equivalent circuit model was served as design foundation.The infrared absorption efficiency was numerically calculated and the mechanism analysis is given in the paper.The simulation results show that all three structures can achieve high absorption efficiency at 10.6μm under TE/TM polarization.The absorption remains high when the incident angle is less than 70°.Experimental results exhibit good accordance with simulation.展开更多
In this paper,we designed a metamaterial absorber performed in microwave frequency band.This absorber is composed of E-shaped dielectrics which are arranged along different directions.The E-shaped all-dielectric struc...In this paper,we designed a metamaterial absorber performed in microwave frequency band.This absorber is composed of E-shaped dielectrics which are arranged along different directions.The E-shaped all-dielectric structure is made of microwave ceramics with high permittivity and low loss.Within about 1 GHz frequency band,more than 86%absorption efficiency was observed for this metamaterial absorber.This absorber is polarization insensitive and is stable for incident angles.It is figured out that the polarization insensitive absorption is caused by the nearly located varied resonant modes which are excited by the E-shaped all-dielectric resonators with the same size but in the different direction.The E-shaped dielectric absorber contains intensive resonant points.Our research work paves a way for designing all-dielectric absorber.展开更多
In order to clarify the Na/K ratios dependence of piezoelectric properties,(K_(1-x)Na_(x))TNbO_(3)cer-amics were prepared by conventional solid-state sintering at a=0.4-0.6 with a smaller com-positional interval(0.02 ...In order to clarify the Na/K ratios dependence of piezoelectric properties,(K_(1-x)Na_(x))TNbO_(3)cer-amics were prepared by conventional solid-state sintering at a=0.4-0.6 with a smaller com-positional interval(0.02 mol).The results demonstrate that the Na/K ratios have obvious effecton piezoelectric and ferroelectric properties of(K_(1-x)Na_(x))NbO_(3)ceramics.Piezoelectric and fer-roelectric properties show the maximum(d_(33)147 pc/N,k_(p)=0.40,and P_(r)=24μC/cm^(2))at=0.54,which is not consistent with conventional viewpoint.The reasons should be attributedto the existence of a phase boundary at a=0.54 mol,which is similar to the morphotropic phaseboundary in Pb(Zr,Ti)O_(3)ceramics.展开更多
基金supports from the National Natural Science Foundation of China under Grant Nos.61971435,62101588,62101589Natural Science Basic Research Program of Shaanxi Province(Grant No:2022JM-352,2022JQ-335,2023-JC-YB-069)the National Key Research and Development Program of China(Grant No.:SQ2017YFA0700201).
文摘Complex-amplitude holographic metasurfaces(CAHMs)with the flexibility in modulating phase and amplitude profiles have been used to manipulate the propagation of wavefront with an unprecedented level,leading to higher image-reconstruction quality compared with their natural counterparts.However,prevailing design methods of CAHMs are based on Huygens-Fresnel theory,meta-atom optimization,numerical simulation and experimental verification,which results in a consumption of computing resources.Here,we applied residual encoder-decoder convolutional neural network to directly map the electric field distributions and input images for monolithic metasurface design.A pretrained network is firstly trained by the electric field distributions calculated by diffraction theory,which is subsequently migrated as transfer learning framework to map the simulated electric field distributions and input images.The training results show that the normalized mean pixel error is about 3%on dataset.As verification,the metasurface prototypes are fabricated,simulated and measured.The reconstructed electric field of reverse-engineered metasurface exhibits high similarity to the target electric field,which demonstrates the effectiveness of our design.Encouragingly,this work provides a monolithic field-to-pattern design method for CAHMs,which paves a new route for the direct reconstruction of metasurfaces.
基金National Key Research and Development Program of China(2022YFB3806200)National Natural Science Foundation of China(61971341,61971435,61971437)。
文摘Polarization is one of the basic characteristics of electromagnetic(EM)waves,and its flexible control is very important in many practical applications.At present,most of the multifunction polarization metasurfaces are electrically tunable based on PIN and varactor diodes,which are easy to operate and have strong real-time performance.However,there are still some problems in them,such as few degrees of freedom of planar structure control,complex circuit,bulky sample,and high cost.In view of these shortcomings,this paper proposes a Miura origami based reconfigurable polarization conversion metasurface for multifunctional control of EM waves.The interaction between the electric dipoles is changed by adjusting the folding angleθ,thereby tuning the operating frequency of the polarization conversion and the polarization state of the reflected wave.This mechanical control method brings more degrees of freedom to manipulate EM waves.And the processed sample is with lightweight and low cost.To verify the performance of the proposed origami polarization converter,a Miura origami structure loaded with metal split rings is designed and fabricated.The operating frequency of the structure can be tuned in different folding states.In addition,by controlling the folding angleθ,linear-to-linear and linear-to-circular polarization converters can be realized at different folding states.The proposed Miura origami polarization conversion metasurface provides a new idea for reconfigurable linear polarization conversion and multifunctional devices.
基金the Natural Science Foun-dation of China(NSFC)through the Grant Nos.11504428,61671466 and 11274389the Natural Science Foundation of Shaanxi Province under Grant 2016JM6026the Inno-vative Team of Shaanxi Province(No.2014KCT-05).
文摘In this work,a quadruple-band dielectric metamaterial absorber(MMA)was proposed and studied,which is composed of eight cuboid dielectric particles and a metallic ground plate.When electromagnetic wave is incident on the dielectric particles,dielectric particles act as resonators and produce abundant resonant modes,which can result in perfect absorption.In simulation,four absorption peaks are observed at 9.13,9.62,10.0 and 10.46 GHz with 88%,89%,100%and 96%,respectively.By adjusting geometry parameters of the dielectric particles,dielectric MMAs with different bands can be obtained.Further investigation shows that the absorption peaks can be changed by increasing the permittivity of the dielectric.Based on the designing technique of using simple cuboid dielectric particles directly acting as resonator,this work provides a simple method to construct multiband alldielectric MMA.
基金the support from the National Natural Science Foundation of China under Grant N1os.11504428,11274389,61331005,61671466the National Natural Science Foundation of Shaanxi under Grant Nos.2016JM6026.
文摘Frequency selective surface(FSS)has been extensively studied due to its potential applications in radomes,antenna reflectors,high-impedance surfaces and absorbers.Recently,a new principle of designing FSS has been proposed and mainly studied in two levels.In the level of materials,dielectric materials instead of metallic patterns are capable of achieving more functional performance in FSS design.Moreover,FSSs made of dielectric materials can be used in different extreme environments,depending on their electrical,thermal or mechanical properties.In the level of design principle,the theory of metamaterial can be used to design FSS in a convenient and concise way.In this review paper,we provide a brief summary about the recent progress in all-dielectric metamaterial frequency selective surface(ADM-FSS).The basic principle of designing ADM-FSS is summarized.As significant tools,Mie theory and dielectric resonator(DR)theory are given which illustrate clearly how they are used in the FSS design.Then,several design cases including dielectric particle-based ADM-FSS and dielectric network-based ADM-FSS are introduced and reviewed.After a discussion of these two types of ADM-FSSs,we reviewed the existing fabrication techniques that are used in building the experiment samples.Finally,issues and challenges regarding the rapid fabrication techniques and further development aspects are discussed.
基金Natural Science Foundation of China(NSFC)through the grant nos.11504428,61671466 and 11274389Natural Science Foundation of Shaanxi Province under Grant 2016JM6026.
文摘In this paper,we demonstrate a method of designing all-dielectric metamaterial frequency selective surface(FSS)with ceramic resonators in spatial arrangement.Compared with the traditional way,spatial arrangement provides a flexible way to handle the permutation and combination of different ceramic resonators.With this method,the resonance response can be adjusted easily to achieve pass/stop band effects.As an example,a stop band spatial arrangement all-dielectric metamaterial FSS is designed.Its working band is in 11.65–12.23 GHz.By adjusting permittivity and geometrical parameters of ceramic resonators,we can easily modulate the resonances,band pass or band stop characteristic,as well as the working band.
基金National Natural Science Foundation of China(51802349,61801509,61901508,61971435,62101588,62101589)National Key Research and Development Program of China(2017YFA0700201)+1 种基金Young Talent Fund of University Association for Science and Technology in Shaanxi(2021JQ-363)Air Force Engineering University Excellent Doctoral Dissertation Support Foundation(KGD080920016).
文摘Reciprocity is ubiquitous in antennas for receiving and radiating electromagnetic(EM) waves, i.e., if an antenna has good receiving performance at a given direction, it also has good radiation performance in that direction.Inspired by this, we propose a method of designing a quasi-ominibearing retro-reflective metagrating(RRMG)protected by the reciprocity of antennas. Based on the second-order mode around 15.0 GHz of a short-circuited structured patch antenna(SPA), incident transverse magnetic waves can be received, channeled into the coaxial lines, reflected by the shortened end, and finally re-radiated into free space with a reversed wave vector. RRMGs are contrived consisting of this identical SPA, with a grating constant allowing ±2nd-, ±1st-, and zeroth-order diffractions. Oblique incidence, plus the tilted nulls of the re-radiation pattern, can eliminate -1st, zeroth,+1st, and +2nd orders, and only the -2nd order is left to achieve retro-reflections. Prototypes were fabricated and measured. Simulated and measured results show that the RRMGs maintain only -2nd-order diffraction for incident angles 32.2° ≤ θ_(i)< 90.0° in four quadrants, and that RRMGs can achieve quasi-omnibearing retro-reflections for θ_(i)= 50.0°. The use of higher-order diffraction brings more degrees of freedom in manipulating EM waves, and this strategy can be readily extended to millimeter waves, THz wave, or even optical regimes.
基金We gratefully acknowledge the financial support from National Natural Science Foundation of China(Grant Nos.61331005,61471388,11204378,11274389,61304393,61302023)the Natural Science Foundation of Shaanxi Province(Grant No.2013JM6005)the Special Funds for Authors of Annual Excellent Doctoral Degree Dissertations of China(Grant No.201242).
文摘In this paper,we propose a novel transmit/reflect switchable frequency selective surface(FSS)in millimeter wave band based on the effective medium theory under quasi-static limit,which is designed with square-hole elements cut from continuum dielectric plates.The building elements of the surface are composed of all dielectric metamaterial rather than metal material.With proper structural design and parameters tuning,the resonance frequencies can be tuned appropriately.The frequency response of the surface can be switched from that of a reflecting structure to a transmitting one by rotating the surface 90°,which means under different incident polarizations.The reflective response can be realized due to the effect of electric and magnetic resonances.Theoretical analysis shows that the reflective response arises from impedance mismatching by electric and magnetic resonances.And the transmitting response is the left-handed passband,arises from the coupling of the electric and magnetic resonances.In addition,effective electromagnetic parameters and the dynamic induced field distributions are analyzed to explain the mechanism of the responses.The method can also be used to design switchable all-dielectric FSS with continuum structures in other frequencies.
基金Young Talent Fund of Association for Science and Technology in Shaanxi (20220102)National Natural Science Foundation of China (61971435,62101588)。
文摘Metasurfaces have provided an unprecedented degree of freedom(DOF)in the manipulation of electromagnetic waves.A geometric phase can be readily obtained by rotating the meta-atoms of a metasurface.Nevertheless,such geometric phases are usually spin-coupled,with the same magnitude but opposite signs for left-and right-handed circularly polarized(LCP and RCP)waves.To achieve independent control of LCP and RCP waves,it is crucial to obtain spin-decoupled geometric phases.In this paper,we propose to obtain completely spin-decoupled geometric phases by engineering the surface current paths on meta-atoms.Based on the rotational Doppler effect,the rotation manner is first analyzed,and it is found that the generation of a geometric phase lies in the rotation of the surface current paths on meta-atoms.Since the induced surface current paths under the LCP and RCP waves always start oppositely and are mirror-symmetrical with each other,it is natural that the geometric phases have the same magnitude and opposite signs when the meta-atoms are rotated.To obtain spin-decoupled geometric phases,the induced surface current under one spin should be rotated by one angle while the current under the other spin is rotated by a different angles.In this way,LCP and RCP waves can acquire different geometric phase changes.Proof-of-principle prototypes were designed,fabricated,and measured.Both the simulation and experiment results verify spin-decoupled geometric phases.This work provides a robust means to obtain a spindependent geometric phase and can be readily extended to higher frequency bands such as the terahertz,IR,and optical regimes.
基金National Natural Science Foundation of China (61971341, 61971435, 61971437)Natural Science Foundation of Shaanxi Province (2020JM-342, 2022JQ-630)。
文摘Chiral mirrors can produce spin selective absorption for left-handed circularly polarized(LCP) or right-handed circularly polarized(RCP) waves. However, the previously proposed chiral mirror only absorbs the designated circularly polarized(CP) wave in the microwave frequency band, lacking versatility in practical applications.Here, we propose a switchable chiral mirror based on a pair of PIN diodes. The switchable chiral mirror has four working states, switching from the handedness-preserving mirror to the LCP mirror, RCP mirror, and perfect absorber. The basis of these advances is to change the chirality of two-dimensional(2D) chiral metamaterials and the circular conversion dichroism related to it, which is the first report in the microwave frequency band.Surface current distributions shed light on how switchable chiral mirrors work by handedness-selective excitation of reflective and absorbing electric dipole modes. Energy loss distributions verify the working mechanism. The thickness of the switchable chiral mirror is one-tenth of the working wavelength, which is suitable for integrated manufacturing. The measurement results are in good agreement with the simulation results.
基金Young Talent Fund of University Association for Science and Technology in Shaanxi(20220102)Fundamental Research Funds of Shaanxi Key Laboratory of ArtificiallyStructured Functional Materials and Devices(AFMD-KFJ-21211)+1 种基金National Key Research and Development Program of China(2017YFA0700201)National Natural Science Foundation of China(61901508,61971435,61971437,62101588)。
文摘Metasurfaces have provided unprecedented degrees of freedom in manipulating electromagnetic waves upon interfaces.In this work,we first explore the condition of wide operating bandwidth in the view of reflective scheme,which indicates the necessity of anomalous dispersion.To this end,the leaky cavity modes(LCMs)in the metaatom are analyzed and can make effective permittivity inversely proportional to frequency.Here we employ the longitudinal Fabry-Perot(F-P)resonances and transverse plasmonic resonances to improve the LCMs efficiency.It is shown that the order of F-P resonance can be customized by the plasmonic modes,that is,the F-P cavity propagation phase should match the phase delay of surface currents excited on the meta-atom.The nth order F-P resonance will multiply the permittivity by a factor of n,allowing larger phase accumulation with increasing frequencies and forming nonlinear phase distribution which can be applied in weak chromatic-aberration focusing design.As a proof-of-concept,we demonstrate a planar weak chromatic-aberration focusing reflector with a thickness ofλ_(0)∕9 at 16.0-21.0 GHz.This work paves a robust way to advanced functional materials with anomalous dispersion and can be extended to higher frequencies such as terahertz,infrared,and optical frequencies.
基金Air Force Engineering University(KGD080921020)Natural Science Basic Research Program of Shaanxi Province(2021JQ-363)+1 种基金Fundamental Research Funds for the Central Universities(2242022k30004)National Natural Science Foundation of China(61901508,61971435,62101589,62201609)。
文摘Metasurfaces have intrigued long-standing research interests and developed multitudinous compelling applications owing to their unprecedented capability for manipulating electromagnetic waves,and the emerging programmable coding metasurfaces(PCMs)provide a real-time reconfigurable platform to dynamically implement customized functions.Nevertheless,most existing PCMs can only act on the single polarization state or perform in the limited polarization channel,which immensely restricts their practical application in multitask intelligent metadevices.Herein,an appealing strategy of the PCM is proposed to realize tunable functions in co-polarized reflection channels of orthogonal circularly polarized waves and in co-polarized and cross-polarized reflection channels of orthogonal linearly polarized waves from 9.0 to 10.5 GHz.In the above six channels,the spindecoupled programmable meta-atom can achieve high-efficiency reflection and 1-bit digital phase modulation by selecting the specific ON/OFF states of two diodes,and the phase coding sequence of the PCM is dynamically regulated by the field-programmable gate array to generate the desired function.A proof-of-concept prototype is constructed to verify the feasibility of our methodology,and numerous simulation and experimental results are in excellent agreement with the theoretical predictions.This inspiring design opens a new avenue for constructing intelligent metasurfaces with higher serviceability and flexibility,and has tremendous application potential in communication,sensing,and other multifunctional smart metadevices.
基金National Key Research and Development Program of China(SQ2017YFA0700201,2017YFA0700202)National Natural Science Foundation of China(61971435,61731010,11874142)
文摘Metasurface has provided unprecedented freedoms in manipulating electromagnetic(EM) waves, exhibiting fascinating functions. Conventionally, these functions are implemented right on metasurfaces, where spatial modulations on EM wave amplitudes or phases are achieved by meta-atoms. This study proposes the concept of virtual metasurface(VM), which is formed by arrays of foci away from the entity metasurface. Unlike conventional metasurfaces, spatial modulations on the amplitudes or phases of EM waves occur in the air, with a focal length distance from the entity metasurface. As a proof of concept, we demonstrated a transmissive VM. The entity metasurface consists of transmissive focusing metasurface tiles(TFMTs) with the same focal length. Two TFMTs were designed with phase difference π to enable the most typical checkerboard configuration. The TFMTs were assembled to form the entity metasurface, whereas their foci formed the VM. Due to the π phase difference among adjacent foci, EM propagation along the normal direction was cancelled, leading to four tilted far-field beams. The concept of VM can be readily extended to higher frequencies from terahertz to optical regimes and may find wide applications in communication, camouflage, and other fields.
基金National Natural Science Foundation of China(61971437,61971341,61971435)Natural Science Foundation of Shaanxi Province(2020JM-342,2022JQ-630)Postdoctoral Science Foundation of China(2019M651644)。
文摘Three-dimensional chiral materials with intrinsic chirality play a crucial role in achieving a strong chiral response and flexible light manipulation.Reconfigurable chirality through the 3D morphological transformation of chiral materials is significant for greater freedom in tailoring light but remains a challenge.Inspired by the unique 3D morphological memory capability of shape memory alloys(SMAs),we demonstrate and discuss a chiral resonator in the microwave regime that can realize reconfigurable chirality through 3D morphological transformation.The introduction of heating film realizes voltage control of SMA’s morphology for utilizing the temperature sensitivity of SMA better,enabling arbitrary control of circular dichroism(CD)flip and CD intensity.The qualitative and quantitative analysis of the surface current distribution of chiral enantiomers reveals that the chirality of metaatoms originates from the surge of electric dipole pxand electric quadrupole Q.It is worth mentioning that the proposed strategy to achieve reconfigurable chirality using 3D morphological transformations can be directly extended to other higher frequencies,such as visible,infrared,and terahertz bands.Significantly,our paradigm to study the relationship between complex 3D morphology and chirality holds potential for application in biosensing,spin detection,and spin-selective devices.
基金Natural Science Basic Research Program of Shaanxi Province(2020JQ-471,2020JQ-472)National Key Research and Development Program of China(SQ2017YFA0700201)National Natural Science Foundation of China(12004437,51802349,61971435).
文摘For camouflage applications,the performance requirements for metamaterials in different electromagnetic spectra are usually contradictory,which makes it difficult to develop satisfactory design schemes with multispectral compatibility.Fortunately,empowered by machine learning,metamaterial design is no longer limited to directly solving Maxwell’s equations.The design schemes and experiences of metamaterials can be analyzed,summarized,and learned by computers,which will significantly improve the design efficiency for the sake of practical engineer-ing applications.Here,we resort to the machine learning to solve the multispectral compatibility problem of metamaterials and demonstrate the design of a new metafilm with multiple mechanisms that can realize small microwave scattering,low infrared emissivity,and visible transparency simultaneously using a multilayer back-propagation neural network.The rapid evolution of structural design is realized by establishing a mapping between spectral curves and structural parameters.By training the network with different materials,the designed network is more adaptable.Through simulations and experimental verifications,the designed architecture has good accuracy and robustness.This paper provides a facile method for fast designs of multispectral metafilms that can find wide applications in satellite solar panels,aircraft windows,and others.
基金Natural Science Foundation of Shaanxi Province(2020JM-342)Beijing Outstanding Young Scientist Program(BJJWZYJH01201910007022)National Natural Science Foundation of China(61775019,61971435,61971437)。
文摘Recently, we have witnessed an extraordinary spurt in attention toward manipulating electromagnetic waves by metasurfaces. Particularly, tailoring of circular polarization has attracted great amounts of interest in both microwave and optics regimes. Circular dichroism, an exotic chiroptical effect of natural molecules, has aroused discussion about this issue, yet it is still in its infancy. Herein, we initiate circular dichroism followed by controlling spin-selective wavefronts via chiral metasurfaces. An N-shaped chiral resonator loaded with two lumped resistors is proposed as the meta-atom producing an adequate phase gradient. Assisted by the ohmic dissipation of the introduced resistors, the effect of differential absorption provides an auxiliary degree of freedom for developing circularly polarized waves with a designated spin state. A planar corner reflector that can achieve retro-reflection and absorption for right-and left-handed circularly polarized incidence is theoretically simulated and experimentally observed at microwave frequency. Thus, our effort provides an alternative approach to tailoring electromagnetic waves in a circular dichroitic manner and may also find applications in multi-functional systems in optics and microwave regimes.
基金National Natural Science Foundation of China under Grant Nos.61971435,62101588,62101589National Key Research and Development Program of China(Grant No.:SQ2017YFA0700201)+1 种基金C.-W.Q.is supported by a grant(R-261-518-004-720|A-0005947-16-00)from Advanced Research and Technology Innovation Centre(ARTIC)in National University of Singapore.
文摘The power of controlling objects with mind has captivated a popular fascination to human beings.One possible path is to employ brain signal collecting technologies together with emerging programmable metasurfaces(PM),whose functions or operating modes can be switched or customized via on-site programming or pre-defined software.Nevertheless,most of existing PMs are wire-connected to users,manually-controlled and not real-time.Here,we propose the concept of remotely mind-controlled metasurface(RMCM)via brainwaves.Rather than DC voltage from power supply or AC voltages from signal generators,the metasurface is controlled by brainwaves collected in real time and transmitted wirelessly from the user.As an example,we demonstrated a RMCM whose scattering pattern can be altered dynamically according to the user’s brain waves via Bluetooth.The attention intensity information is extracted as the control signal and a mapping between attention intensity and scattering pattern of the metasurface is established.With such a framework,we experimentally demonstrated and verified a prototype of such metasurface system which can be remotely controlled by the user to modify its scattering pattern.This work paves a new way to intelligent metasurfaces and may find applications in health monitoring,5G/6G communications,smart sensors,etc.
基金supported by the National Key Research and Development Program of China (Grant No. 2021YFA1401200)the National Natural Science Foundation of China (Grant Nos. 61971437, 92050117, and U21A20140)+2 种基金the Beijing Outstanding Young Scientist Program (Grant No.BJJWZYJH01201910007022)the Natural Science Foundation of Shaanxi Province (Grant Nos. 2020JM-342, and 2022JM-352)the Beijing Institute of Technology Research Fund Program for Young Scholars (Grant No. XSQD-201904005)。
文摘Chirality, as one of the ubiquitous properties in nature, has aroused striking attention in the fields of physics and materials sciences. For tailoring of light with more degree of freedom, circular dichroism has been considered as the auxiliary dimension to improving such an issue. Inspired by the Born-Kuhn plasmonic oscillation model, we demonstrate and discuss a chiral resonator to reveal reverse circular dichroism within two separate frequency bands in the microwave regime. The underlying physical mechanisms of bonding and anti-bounding modes are analyzed via transmission/reflection spectra and surface current distributions for different chiral enantiomers. To leverage the proposed paradigm to the application levels, especially for metaholography, we conduct the numerical simulation and experimental demonstration of two proofs of principles. Based on the Pancharatnam-Berry phase/amplitude modulation and complex-amplitude manipulation, respectively, the meta-holograms with independent targets of reconstructing images in full-space and reflected regions are achieved. Significantly, our paradigm may promise further applications in spin-controlled meta-devices for image processing, information encryption, anti-counterfeiting,remote sensing, and radar systems.
基金the support from National Science Foundation of China under Grant Nos.61501497,61331005 and 61671467the special foundation of New-star Plan of Science and technology,No.2015KJXX-47.
文摘In this work,an optical transparent infrared high absorption metamaterial absorber is proposed based on indium tin oxide(ITO)substrate.Due to the fact that ITO holds high reflectivity property in infrared region while transparent in optical region,ITO can be used in the application of Surface Plasmon Polaritons.In this design,three kinds of infrared metamaterial absorbers were proposed.All of them can achieve high absorption at 10.6μm while remaining transparent in visible region.LC equivalent circuit model was served as design foundation.The infrared absorption efficiency was numerically calculated and the mechanism analysis is given in the paper.The simulation results show that all three structures can achieve high absorption efficiency at 10.6μm under TE/TM polarization.The absorption remains high when the incident angle is less than 70°.Experimental results exhibit good accordance with simulation.
基金Natural Science Foundation of China(NSFC)through the grant Nos.61331005,11204378 and 11274389.
文摘In this paper,we designed a metamaterial absorber performed in microwave frequency band.This absorber is composed of E-shaped dielectrics which are arranged along different directions.The E-shaped all-dielectric structure is made of microwave ceramics with high permittivity and low loss.Within about 1 GHz frequency band,more than 86%absorption efficiency was observed for this metamaterial absorber.This absorber is polarization insensitive and is stable for incident angles.It is figured out that the polarization insensitive absorption is caused by the nearly located varied resonant modes which are excited by the E-shaped all-dielectric resonators with the same size but in the different direction.The E-shaped dielectric absorber contains intensive resonant points.Our research work paves a way for designing all-dielectric absorber.
基金supported by National Natural Science Foundation(No.10804130,No.50872107 and No.60871027)Shaanxi Provincial Natural Science Foundation(No.2009JQ1001)State Key Laboratory of Electrical Insulation and Power Equipment(EIPE10202).
文摘In order to clarify the Na/K ratios dependence of piezoelectric properties,(K_(1-x)Na_(x))TNbO_(3)cer-amics were prepared by conventional solid-state sintering at a=0.4-0.6 with a smaller com-positional interval(0.02 mol).The results demonstrate that the Na/K ratios have obvious effecton piezoelectric and ferroelectric properties of(K_(1-x)Na_(x))NbO_(3)ceramics.Piezoelectric and fer-roelectric properties show the maximum(d_(33)147 pc/N,k_(p)=0.40,and P_(r)=24μC/cm^(2))at=0.54,which is not consistent with conventional viewpoint.The reasons should be attributedto the existence of a phase boundary at a=0.54 mol,which is similar to the morphotropic phaseboundary in Pb(Zr,Ti)O_(3)ceramics.