An externally perceivable smart leaky-wave antenna based on spoof surface plasmon polaritons

Smart antennas have received great attention for their potentials to enable communication and perception functions at the same time.However,realizing the function synthesis remains an open challenge,and most existing system solutions are limited to narrow operating bands and high complexity and cost.Here,we propose an externally perceivable leakywave antenna(LWA)based on spoof surface plasmon polaritons(SSPPs),which can realize adaptive real-time switching between the“radiating”and“non-radiating”states and beam tracking at different frequencies.With the assistance of computer vision,the smart SSPP-LWA is able to detect the external target user or jammer,and intelligently track the target by self-adjusting the operating frequency.The proposed scheme helps to reduce the power consumption through dynamically controlling the radiating state of the antenna,and improve spectrum utilization and avoid spectrum conflicts through intelligently deciding the radiating frequency.On the other hand,it is also helpful for the physical layer communication security through switching the antenna working state according to the presence of the target and target beam tracking in real time.In addition,the proposed smart antenna can be generalized to other metamaterial systems and could be a candidate for synaesthesia integration in future smart antenna systems.

A Planar 4-Bit Reconfigurable Antenna Array Based on the Design Philosophy of Information Metasurfaces

Inspired by the design philosophy of information metasurfaces based on the digital coding concept,a planar 4-bit reconfigurable antenna array with low profile of 0.15λ0(whereλ0is the free-space wavelength)is presented.The array is based on a digital coding radiation element consisting of a 1-bit magnetoelectric(ME)dipole and a miniaturized reflection-type phase shifter(RTPS).The proposed 1-bit ME dipole can provide two digital states of"0"and"1"(with 0°and 180°phase responses)over a wide frequency band by individually exciting its two symmetrical feeding ports.The designed RTPS is able to realize a relative phase shift of 173°.By digitally quantizing its phase in the range of 157.5°,additional eight digital states at intervals of 22.5°are obtained.To achieve low sidelobe levels,a 1:16 power divider based on the Taylor line source method is employed to feed the array,A prototype of the proposed 4-bit antenna array has been fabricated and tested,and the experimental results are in good agreement with the simulations.Scanning beams within a±45°range were measured with a maximum realized gain of 13.4 dBi at12 GHz.The sidelobe and cross-polarization levels are below-14.3 and-23.0 dB,respectively.Furthermore,the beam pointing error is within 0.8°,and the 3 dB gain bandwidth of the broadside beam is 25%.Due to its outstanding performance,the array holds potential for significant applications in radar and wireless communication systems.

一种小型化人工表面等离激元传感系统——实现自适应和高灵敏的气体检测

Resonantly enhanced dielectric sensing has superior sensitivity and accuracy because the signal is measured from relative resonance shifts that are immune to signal fluctuations.For applications in the Internet of Things(IoT),accurate detection of resonance frequency shifts using a compact circuit is in high demand.We proposed an ultracompact integrated sensing system that merges a spoof surface plasmon resonance sensor with signal detection,processing,and wireless communication.A softwaredefined scheme was developed to track the resonance shift,which minimized the hardware circuit and made the detection adaptive to the target resonance.A microwave spoof surface plasmon resonator was designed to enhance sensitivity and resonance intensity.The integrated sensing system was constructed on a printed circuit board with dimensions of 1.8 cm×1.2 cm and connected to a smartphone wirelessly through Bluetooth,working in both frequency scanning mode and resonance tracking mode and achieving a signal-to-noise ratio of 69 dB in acetone vapor sensing.This study provides an ultracompact,accurate,adaptive,sensitive,and wireless solution for resonant sensors in the IoT.

Active odd-mode-metachannel for single-conductor systems

Although tremendous efforts have been devoted to investigating planar single-conductor circuits,it remains challenging to provide tight confinement of electromagnetic field and compatibility with active semi-conductor components such as amplifier,harmonic generator and mixers.Single-conductor spoof surface plasmon polariton(SSPP)structure,which is one of the most promising planar single-conductor transmission media due to the outstanding field confinement,still suf-fers from the difficulty in integrating with the active semi-conductor components.In this paper,a new kind of odd-mode-metachannel(OMM)that can support odd-mode SSPPs is proposed to perform as the fundamental transmission chan-nel of the single-conductor systems.By introducing zigzag decoration,the OMM can strengthen the field confinement and broaden the bandwidth of odd-mode SSPPs simultaneously.More importantly,the active semi-conductor amplifier chip integration is achieved by utilizing the intrinsic potential difference on OMM,which breaks the major obstacle in im-plementing the single-conductor systems.As an instance,an amplifier is successfully integrated on the single-conductor OMM,which can realize both loss compensation and signal amplification.Meanwhile,the merits of OMM including crosstalk suppression,low radar cross section(RCS),and flexibility are comprehensively demonstrated.Hence,the pro-posed OMM and its capability to integrate with the active semi-conductor components may provide a new avenue to fu-ture single-conductor conformal systems and smart skins.

Artificial intelligence-assisted chiral nanophotonic designs

Chiral nanostructures can enhance the weak inherent chiral effects of biomolecules and highlight the important roles in chiral detection.However,the design of the chiral nanostructures is challenged by extensive theoretical simulations and explorative experiments.Recently,Zheyu Fang’s group proposed a chiral nanostructure design method based on reinforcement learning,which can find out metallic chiral nanostructures with a sharp peak in circular dichroism spectra and enhance the chiral detection signals.This work envisions the powerful roles of artificial intelligence in nanophotonic designs.

Frequency-modulated continuous waves controlled by space-time-coding metasurface with nonlinearly periodic phases

The rapid development of space-time-coding metasurfaces(STCMs)offers a new avenue to manipulate spatial electromagnetic beams,waveforms,and frequency spectra simultaneously with high efficiency.To date,most studies are primarily focused on harmonic generations and independent controls of finite-order harmonics and their spatial waves,but the manipulations of continuously temporal waveforms that include much rich frequency spectral components are still limited in both theory and experiment based on STCM.Here,we propose a theoretical framework and method to generate frequency-modulated continuous waves(FMCWs)and control their spatial propagation behaviors simultaneously via a novel STCM with nonlinearly periodic phases.Since the carrier frequency of FMCW changes with time rapidly,we can produce customized time-varying reflection phases at will by the required FMCW under the illumination of a monochromatic wave.More importantly,the propagation directions of the time-varying beams can be controlled by encoding the metasurface with different initial phase gradients.A programmable STCM prototype with a full-phase range is designed and fabricated to realize reprogrammable FMCW functions,and experimental results show good agreement with the theoretical analyses.

Space-Time-Coding Digital Metasurfaces:Principles and Applications

Space-time-modulated metastructures characterized by spatiotemporally varying properties have recently attracted great interest and become one of the most fascinating and promising research fields.In the meantime,space-time-coding digital metasurfaces with inherently programmable natures emerge as powerful and versatile platforms for implementing the spatiotemporal modulations,which have been successfully realized and used to manipulate the electromagnetic waves in both the spectral and spatial domains.In this article,we systematically introduce the general concepts and working principles of space-time-coding digital metasurfaces and provide a comprehensive survey of recent advances and representative applications in this field.Specifically,we illustrate the examples of complicated wave manipulations,including harmonic beam control and programmable nonreciprocal effect.The fascinating strategy of space-time-coding opens the door to exciting scenarios for information systems,with abundant applications ranging from wireless communications to imaging and radars.We summarize this review by presenting the perspectives on the existing challenges and future directions in this fast-growing research field.

Harmonic information transitions of spatiotemporal metasurfaces

Facilitated by ultrafast dynamic modulations,spatiotemporal metasurfaces have been identified as a pivotal platform for manipulating electromagnetic waves and creating exotic physical phenomena,such as dispersion cancellation,Lorentz reciprocity breakage,and Doppler illusions.Motivated by emerging information-oriented technologies,we hereby probe the information transition mechanisms induced by spatiotemporal variations and present a general model to characterize the information processing capabilities of the spatiotemporal metasurface.Group theory and abstract number theory are adopted through this investigation,by which the group extension and independent controls of multiple harmonics are proposed and demonstrated as two major tools for information transitions from the spatiotemporal domain to the spectra-wavevector domain.By incorporating Shannon’s entropy theory into the proposed model,we further discover the corresponding information transition efficiencies and the upper bound of the channel capacity of the spatiotemporal metasurface.The results of harmonic information transitions show great potential in achieving high-capacity versatile information processing systems with spatiotemporal metasurfaces.

Directly wireless communication of human minds via non-invasive brain-computer-metasurface platform

Brain-computer interfaces(BCIs),invasive or non-invasive,have projected unparalleled vision and promise for assisting patients in need to better their interaction with the surroundings.Inspired by the BCI-based rehabilitation technologies for nerve-system impairments and amputation,we propose an electromagnetic brain-computer-metasurface(EBCM)paradigm,regulated by human’s cognition by brain signals directly and non-invasively.We experimentally show that our EBCM platform can translate human’s mind from evoked potentials of P300-based electroencephalography to digital coding information in the electromagnetic domain non-invasively,which can be further processed and transported by an information metasurface in automated and wireless fashions.Directly wireless communications of the human minds are performed between two EBCM operators with accurate text transmissions.Moreover,several other proof-of-concept mind-control schemes are presented using the same EBCM platform,exhibiting flexibly-customized capabilities of information processing and synthesis like visual-beam scanning,wave modulations,and pattern encoding.

Glide symmetry for mode control and significant suppression of coupling in dual-strip SSPP transmission lines

Glide symmetry,which is one kind of higher symmetry,is introduced in a special type of plasmonic metamaterial,the transmission lines(TLs)of spoof surface plasmon polaritons(SSPPs),in order to control the dispersion characteristics and modal fields of the SSPPs.We show that the glide-symmetric TL presents merged pass bands and mode degeneracy,which lead to broad working bandwidth and extremely low coupling between neighboring TLs.Dual-conductor SSPP TLs with and without glide symmetry are arranged in parallel as two channels with very deep subwavelength separation(e.g.,λ0∕100 at 5 GHz)for the application of integrated circuits and systems.Mutual coupling between the hybrid channels is analyzed using coupled mode theory and characterized in terms of scattering parameters and near-field distributions.We demonstrate theoretically and experimentally that the hybrid TL array obtains significantly more suppressed crosstalk than the uniform array of two nonglide symmetric TLs.Hence,it is concluded that the glide symmetry can be adopted to flexibly design the propagation of SSPPs and benefit the development of highly compact plasmonic circuits.

Simultaneous wireless information and power transfer transmitting architecture based on asynchronous space-time-coding digital metasurface[Invited]

Simultaneous wireless information and power transfer(SWIPT)architecture is commonly applied in wireless sensors or Internet of Things(IoT)devices,providing both wireless power sources and communication channels.However,the traditional SWIPT transmitter usually suffers from cross-talk distortion caused by the high peak-to-average power ratio of the input signal and the reduction of power amplifier efficiency.This paper proposes a SWIPT transmitting architecture based on an asynchronous space-time-coding digital metasurface(ASTCM).High-efficiency simultaneous transfer of information and power is achieved via energy distribution and information processing of the wireless monophonic signal reflected from the metasurface.We demonstrate the feasibility of the proposed method through theoretical derivations and experimental verification,which is therefore believed to have great potential in wireless communications and the IoT devices.

Arbitrarily rotating polarization direction and manipulating phases in linear and nonlinear ways using programmable metasurface

Independent controls of various properties of electromagnetic(EM)waves are crucially required in a wide range of applications.Programmable metasurface is a promising candidate to provide an advanced platform for manipulating EM waves.Here,we propose an approach that can arbitrarily control the polarization direction and phases of reflected waves in linear and nonlinear ways using a stacked programmable metasurface.Further,we extend the space-timecoding theory to incorporate the dimension of polarization,which provides an extra degree of freedom for manipulating EM waves.As proof-of-principle application examples,we consider polarization rotation,phase manipulation,and beam steering at linear and nonlinear frequencies.For validation,we design,fabricate,and measure a metasurface sample.The experimental results show good agreement with theoretical predictions and simulations.The proposed approach has a wide range of applications in various areas,such as imaging,data storage,and wireless communication.

Ultrafast modulable 2DEG Huygens metasurface

Huygens metasurfaces have demonstrated remarkable potential in perfect transmission and precise wavefront modulation through the synergistic integration of electric resonance and magnetic resonance.However,prevailing active or reconfigurable Huygens metasurfaces,based on all-optical systems,encounter formidable challenges associated with the intricate control of bulk dielectric using laser equipment and the presence of residual thermal effects,leading to limitations in continuous modulation speeds.Here,we present an ultrafast electrically driven terahertz Huygens metasurface that comprises an artificial microstructure layer featuring a two-dimensional electron gas(2DEG)provided by an AlGaN/GaN heterojunction,as well as a passive microstructure layer.Through precise manipulation of the carrier concentration within the 2DEG layer,we effectively govern the current distribution on the metasurfaces,inducing variations in electromagnetic resonance modes to modulate terahertz waves.This modulation mechanism achieves high efficiency and contrast for terahertz wave manipulation.Experimental investigations demonstrate continuous modulation capabilities of up to 6 GHz,a modulation efficiency of 90%,a transmission of 91%,and a remarkable relative operating bandwidth of 55.5%.These significant advancements substantially enhance the performance of terahertz metasurface modulators.Importantly,our work not only enables efficient amplitude modulation but also introduces an approach for the development of high-speed and efficient intelligent transmissive metasurfaces.

Intelligent coding metasurface holograms by physics-assisted unsupervised generative adversarial network

Intelligent coding metasurface is a kind of information-carrying metasurface that can manipulate electromagnetic waves and associate digital information simultaneously in a smart way.One of its widely explored applications is to develop advanced schemes of dynamic holographic imaging.By now,the controlling coding sequences of the metasurface are usually designed by performing iterative approaches,including the Gerchberg–Saxton(GS)algorithm and stochastic optimization algorithm,which set a large barrier on the deployment of the intelligent coding metasurface in many practical scenarios with strong demands on high efficiency and capability.Here,we propose an efficient non-iterative algorithm for designing intelligent coding metasurface holograms in the context of unsupervised conditional generative adversarial networks(cGANs),which is referred to as physics-driven variational auto-encoder(VAE)cGAN(VAE-cGAN).Sharply different from the conventional cGAN with a harsh requirement on a large amount of manual-marked training data,the proposed VAE-cGAN behaves in a physics-driving way and thus can fundamentally remove the difficulties in the conventional cGAN.Specifically,the physical operation mechanism between the electric-field distribution and metasurface is introduced to model the VAE decoding module of the developed VAE-cGAN.Selected simulation and experimental results have been provided to demonstrate the state-of-the-art reliability and high efficiency of our VAE-cGAN.It could be faithfully expected that smart holograms could be developed by deploying our VAE-cGAN on neural network chips,finding more valuable applications in communication,microscopy,and so on.

Machine-learning-empowered multispectral metafilm with reduced radar cross section,low infrared emissivity,and visible transparency

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.

Extensible on-chip mode manipulations based on metamaterials

An extensible framework is proposed for on-chip spatial-mode manipulations based on metamaterial building blocks,which enables the excitation of arbitrarily high-order spatial modes in silicon waveguides.It makes a significant step towards the comprehensive and on-chip manipulations of spatial lights,and may provide promising opportunities for complex photonic functionalities.

Information metasurfaces and intelligent metasurfaces

Metamaterials and metasurfaces have inspired worldwide interest in the recent two decades due to their extraordinary performance in controlling material parameters and electromagnetic properties.However,most studies on metamaterials and metasurfaces are focused on manipulations of electromagnetic fields and waves,because of their analog natures.The concepts of digital coding and programmable metasurfaces proposed in 2014 have opened a new perspective to characterize and design metasurfaces in a digital way,and made it possible to control electromagnetic fields/waves and process digital information simultaneously,yielding the birth of a new direction of information metasurfaces.On the other hand,artificial intelligence(AI)has become more important in automatic designs of metasurfaces.In this review paper,we first show the intrinsic natures and advantages of information metasurfaces,including information operations,programmable and real-time control capabilities,and space–time-coding strategies.Then we introduce the recent advances in designing metasurfaces using AI technologies,and particularly discuss the close combinations of information metasurfaces and AI to generate intelligent metasurfaces.We present self-adaptively smart metasurfaces,AI-based intelligent imagers,microwave cameras,and programmable AI machines based on optical neural networks.Finally,we indicate the challenges,applications,and future directions of information and intelligent metasurfaces.

Reconfigurable intelligent surface with high optical-transparency based on metalmesh

Reconfigurable intelligent surfaces(RISs)have aroused extensive attentions from academic and wireless communication communities due to their abilities to customize the electromagnetic(EM)characteristics of the propagation channels flexibly and rapidly.Recent advances in theoretical innovations and prototype systems have demonstrated the advantages of RISs in terms of low cost,low power consumption,and easy deployment.Meanwhile,the optically transparent RISs are demanded in some application scenarios.In this paper,we propose a 2-bit metalmesh-based RIS with high optical-transparency.By analyzing the surface current distributions on the element,we employ the metalmesh-grid patterns and metalmesh-stripe patterns on the top and ground layers respectively.The metalmesh patterns can help improve the optical transparency of RISs,while maintaining similar microwave characteristics.The RIS can reach the optical transparency of 79%,and the reflection amplitude is greater than3.2 dB within the operating band.Finally,to verify the capability of the proposed RIS in wavefront controls,the far-field scattering patterns of the RIS with different coding sequences are investigated and the simulation results are in good agreement with the theoretical results.