Type Of Metasurface Research Articles

Analysis of binary huygens metasurfaces under non-planar illumination

In this article, we have investigated the effect of using a real feed on the performance of one-dimensional binary Huygens metasurfaces (BHMS). The designed structure has variable periods and each unit-cell consists of two dipoles with different lengths. Floquet theory and local constant period assumption are used to design these metasurfaces. The simulation results show the high efficiency of the designed structure and its beam squint capability. The results in this article make it possible to use this type of metasurface in real applications under the illumination of real feed sources.

Engineered metagrating as shield from surface Rayleigh waves

Rayleigh wave isolation using metamaterials is a research hotspot in the engineering community, yet the development of relevant mitigation methods remains an open and challenging problem. Herein, we propose a new type of metasurface, known as an engineered metagrating, which is a special metasurface buried in soil and plays a role in shielding surface Rayleigh waves. Moreover, the total omnidirectional reflection characteristics and subwavelength properties exhibited by the proposed metasurface provide a more flexible reference for surface Rayleigh wave mitigation measures in practical engineering applications. This work can open new avenues for controlling the propagation of seismic surface waves.

RIS-Assisted Hybrid Beamforming and Connected User Vehicle Localization for Millimeter Wave MIMO Systems

A reconfigurable intelligent surface (RIS) is a type of metasurface that can dynamically control the reflection and transmission of electromagnetic waves, such as radio waves, by changing its physical properties. Recently, RISs have played an important role in intelligently reshaping wireless propagation environments to improve the received signal gain as well as spectral efficiency performance. In this paper, we consider a millimeter wave (mmWave) vehicle-to-vehicle (V2V) multiple-input multiple-output (MIMO) system in which, an RIS is deployed to aid downlink V2V data transmission. In particular, the line-of-sight path of the mmWave system is affected by blockages, resulting in higher signaling overhead. Thus, the system performance may suffer due to interruptions caused by static or mobile blockers, such as buildings, trees, vehicles, and pedestrians. In this paper, we propose an RIS-assisted hybrid beamforming scheme for blockage-aware mmWave V2V MIMO systems to increase communication service coverage. First, we propose a conjugate gradient and location-based hybrid beamforming (CG-LHB) algorithm to solve the user sub-rate maximization problem. We then propose a double-step iterative algorithm that utilizes an error covariance matrix splitting method to minimize the effect of location error on the passive beamforming. The proposed algorithms perform quite well when the channel uncertainty is smaller than 10%. Finally, the simulation results validate the proposed CG-LHB algorithm in terms of the RIS-assisted equivalent channel for mmWave V2V MIMO communications.

Ultra-compact active induced-magnetism Huygens’ metasurfaces: design and application

Recently, a new type of metasurface, the induced-magnetism Huygens’ metasurface, has attracted considerable attention due to its capability to manipulate electromagnetic waves. However, these studies mainly work in a passive way such that the functionalities are fixed once fabricated, limiting the device’s adaptability for practical applications and future commercialization. To comply with potential applications, further research endeavors need to be exerted to advance the reconfigurability and practicality. Herein, an ultra-compact and dynamically tunable design strategy of an induced-magnetism Huygens’ metasurface is proposed, whose basic unit is a pair of electric dipoles separated by a dielectric spacer and integrated with a varactor in each electric dipole. By simply changing the driven voltage of each unit, the transmission phase can be individually tuned in the near 2π range; meanwhile, the transmission amplitude remains very high. As a proof-of-concept demonstration, an active magnetism induced Huygens’ meta-lens is proposed to exhibit excellent dynamic wavefront manipulation performance. The proposed method may open an avenue toward planar lightweight low-cost dynamic wavefront manipulation devices.

Metasurface Enabled On-Chip Generation and Manipulation of Vector Beams from Vertical Cavity Surface-Emitting Lasers.

Metasurface polarization optics that consist of 2D array of birefringent nano-antennas have proven remarkable capabilities to generate and manipulate vectorial fields with subwavelength resolution and high efficiency. Integrating this new type of metasurface with the standard vertical cavity surface-emitting laser (VCSEL) platform enables an ultracompact and powerful solution to control both phase and polarization properties of the laser on a chip, which allows to structure a VCSEL into vector beams with on-demand wavefronts. Here, this concept is demonstrated by directly generating versatile vector beams from commercially available VCSELs through on-chip integration of high-index dielectric metasurfaces. Experimentally, the versatility of the approach for the development of vectorial VCSELs are validated by implementing a variety of functionalities, including directional emission of multibeam with specified polarizations, vectorial holographic display, and vector vortex beams generations. Notably, the proposed vectorial VCSELs integrated with a single layer of beam shaping metasurface bypass the requirements of multiple cascaded optical components, and thus have the potential to promote the advancements of ultracompact, lightweight, and scalable vector beams sources, enriching and expanding the applications of VCSELs in optical communications, laser manipulation and processing, information encryption, and quantum optics.

Terraced slopes as large scale natural seismic metasurfaces

In this work, a new type of metasurface which could be applied for surface waves attenuation is numerically examined. Terraced slopes are examined numerically for their applicability of attenuating surface waves. The calculations were performed by using the finite element method. The research includes an investigation for all the geometric parameters of the structure, and how its performance as a metasurface is being affected by the values of each parameter. The proposed terraced slopes can be found in many places either as a natural morphology of the ground or, in most cases, as an artificial ground formation. The findings of this work strongly indicate that the morphology of the sloped surface is fundamental regarding its potential of performing as a large-scale natural metasurface.

Stiffness tuning of a functional-switchable active coding elastic metasurface

Recently, a new type of metasurface namely coding metasurface has emerged as a new technology in manipulating waves. Based on its R-bit, a coding metasurface utilizes 2R of coding units to achieve real-time wave controls which makes the operation of a metasurface easier. Although coding metasurfaces have simpler configurations than conventional metasurfaces, it is yet unavoidable to have structural reconfiguration of metasurface in order to perform different functionalities in single or different frequencies. To overcome this drawback, a functionally switchable 3-bit active coding elastic metasurface comprised of stacked piezoelectric patches shunted with negative capacitance circuit is proposed to manipulate elastic longitudinal waves. By tuning the negative capacitance in the circuitry element, arbitrary tuning of stiffness can be attained which leads to the coverage of full 2π phase range without modifying the structure of metasurface. In addition, analytical model and numerical simulations are developed to verify capability of the proposed coding metasurface for covering full 2π phase shift besides having high transmission at the same time. By utilizing the 8 fundamental coding units with different phase response, the proposed metasurface is designed and simulated based on a finite element approach to illustrate switchable functionalities such as arbitrary refraction and wave focusing, which can be realized through proper tuning of the negative capacitance, in broadband frequencies.

Light absorption and nanofocusing on a tapered magnetic metasurface

A type of metasurface was constructed on a silicon wafer using a nanopatterned magnetic film to achieve ideal light absorption within a wide wavelength range of 3 μm–15 μm. Using the metasurface, the surface electrons could be localized efficiently into an arrayed planar magnetic nanotip and then modulated by configuring the surface architecture to produce remarkable infrared reflectivity variation. A theoretical analysis showed that the excited surface plasmon exhibit stronger electric field components at the common metal-to-air interface. The Tb14Fe68Co18 nanotip array provided more powerful nanofocusing and a lower infrared reflectivity than an array shaped on a traditional aluminum film. By adjusting the structural parameters of the nanorhombus array formed on the TbCo film system, the convergent light spot could be modulated to improve light absorption markedly.

Optical nonlinearity and non-reciprocal transmission of graphene integrated metasurface

Non-reciprocal phenomena generated by optical nonlinear effects without the requirement of external bias have important applications in modern photonics. In this paper, an optical nonlinear metasurface based on monolayer graphene integrated silicon resonant gratings is proposed. It is numerically confirmed that this type of metasurface can excite high-Q guided mode resonances in the communication band with normal incidence. Significant optical Kerr effect is achieved in the metasurface through high third-order polarization coefficient of graphene, and by changing the width and depth of the grating, the nonlinear effect of the metasurface can be effectively controlled to realize the application under different illumination conditions. In addition, remarkable non-reciprocity phenomenon is realized at an incident intensity of 0.085 GW/m2. As an example, with a forward transmittance of 0.732 and a backward transmittance of 0.025, an optical diode is implemented at 1549.1 nm.

Ultra-wide band gap metasurfaces for controlling seismic surface waves

Metamaterials have been widely studied for their advantage in the effective control of the propagation of mechanical waves. However, existing methods are limited in controlling the propagation of seismic surface waves and hardly are put in practical engineering applications. To overcome this limitation, we introduce a new type of metasurface with ultra-wide band gaps for controlling the seismic surface waves, which can be further applied to engineering applications. The metasurface is designed by using an easy and simple method named the destructive interference, rather than the local resonance observed in previous methods. Furthermore, the designed unit structure can construct a periodic structure by using the functional gradient design and combination arrangement, which results in hitherto better or even unprecedented performance in controlling the propagation of seismic surface waves. Moreover, the proposed metasurface provides new opportunities for practical engineering applications, as demonstrated by the metabridge can effectively protect the bridge from the damage of earthquakes.

Polarization‐Sensitive Dielectric Membrane Metasurfaces

AbstractDielectric metasurfaces composed of subwavelength resonators are widely employed for manipulating electromagnetic waves over a broad frequency spectrum ranging from microwaves to optics. Here, a novel type of metasurfaces, created by a periodic lattice of elliptical holes fabricated in a thin dielectric membrane, is studied both theoretically and experimentally. Such membrane metasurfaces demonstrate polarization‐selective behavior, and they change their specific functionality from a reflective magnetic mirror, for one polarization, to a transparent Huygens' surface, for the orthogonal polarization. Such a polarization dependence is achieved by manipulating the interference of Mie‐resonant multipoles through optimizing the design of the elliptic holes in the dielectric membrane. Such membrane metasurfaces can be employed as flat components with polarization‐multiplexed functionalities, bringing benefits for the integration of ultracompact signal manipulation systems.

Design of a new metasurface and its application for linear to circular polarisation conversion

ABSTRACT A new type of metasurface (MTS) structure consisting of two diagonally connected rings is proposed. Proposed MTS with 16-unit cells are arranged in 4 × 4 cells, which converts linearly polarised (LP) to circularly polarised (CP) wave with axial ratio bandwidth (ARBW) of 50 MHz. Four different LP antennas, microstrip fed, coaxial fed, slot antenna, and aperture antenna have been used to test the utility of the MTS for conversion LP to CP. LP to CP has been achieved by merely placing MTS as a superstrate above these antennas. Microstrip antenna has impedance matching bandwidth (IMBW)170 MHz (2.51–2.68 GHz) while ARBW is 20 MHz(2.52–2.56 GHz). The coax fed has IMBW 100 MHz (2.5–2.6 GHz), and ARBW is 50 MHz(2.53–2.58 GHz). Slot antenna has IMBW 830 MHz(2.16–2.99 GHz); however, ARBW is 80 MHz (2.40–2.48 GHz). Aperture antenna has IMBW 710 MHz(2.16–2.87 GHz), and ARBW is 80 MHz(2.56–2.64 GHz). Coaxial fed and aperture antenna have fabricated with the MTS, and their measured results agreed well with simulated, which validate the effectiveness of the proposed metasurface. The proposed MTS could be useful as a polarisation converter in S-band for any antenna.

Multi-Beam Forming and Controls by Metasurface With Phase and Amplitude Modulations

Owing to the capability of providing a certain phase gradient on the interface between two media, metasurfaces have shown great promise for altering the directions of outgoing electromagnetic (EM) waves arbitrarily. With the suitable arrangement of particles on metasurfaces, anomalous reflection and refraction have been observed in wide frequency ranges. To completely control the propagation of EM waves, both phase and amplitude profiles are required in some applications. Herein, we propose a new type of metasurface with both phase and amplitude modulations, which is composed of C-shaped particles and can generate and control multiple beams using amplitude and phase responses simultaneously. An addition theorem of complex reflection coefficients is presented to acquire various states of multiple beams reflected from designed metasurfaces. Meanwhile, the intensities of multiple beams can be separately modulated as desired benefitting from the independent controls of phase and amplitude profiles. All the experimental results have good agreements with the numerical simulations. The presented method opens a new way to form and manipulate multiple beams using metasurfaces, which can find potential applications in beam shaping, radar detection systems, and high-quality holography.

Near-IR wide-field-of-view Huygens metalens for outdoor imaging applications

Abstract The ongoing effort to implement compact and cheap optical systems is the main driving force for the recent flourishing research in the field of optical metalenses. Metalenses are a type of metasurface, used for focusing and imaging applications, and are implemented based on the nanopatterning of an optical surface. The challenge faced by metalens research is to reach high levels of performance using simple fabrication methods suitable for mass production. In this paper, we present a Huygens nanoantenna-based metalens, designed for outdoor photographic/surveillance applications in the near infrared. We show that good imaging quality can be obtained over a field of view as large as ±15°. This first successful implementation of metalenses for outdoor imaging applications is expected to provide insight and inspiration for future metalens imaging applications.

Anomalous refraction manipulation of Lamb waves using single-groove metasurfaces

Inspired by the studies on defects in nondestructive monitoring techniques, we propose a new type of metasurface with single-groove array to manipulate Lamb waves in plate structures along arbitrary trajectories. Because of the interaction between the groove and the Lamb waves, the phase of a transmitted wave varies with the groove position. We manipulated a transmitted wave by optimizing the groove position on the metasurface and realized abnormal refraction, self-accelerating acoustic beams, and source illusion devices. The numerical results confirmed the broadband and robustness of the metasurface in terms of its wave manipulation capability, providing a basis for the design of wave control devices. The proposed method has potential applications in the fields of structural nondestructive testing, vibration control, and signal modulation.

Wideband and high‐gain circularly polarised microstrip antenna design using sandwiched metasurfaces and partially reflecting surface

In this study, the authors propose a new type of metasurface, namely a sandwiched anisotropic metasurface, for converting a linearly polarised elliptical patch antenna into a wideband circularly polarised antenna. A partially reflecting surface (PRS) as a superstrate is further used to enhance the gain of the antenna. The design rules of the antenna are also presented. The combined metasurface and the PRS-based patch antenna is designed on a low-cost substrate FR-4. The realised 3 dB axial ratio bandwidth (ARBW) of the antenna is 1.01 GHz (3.55-4.56 GHz), its impedance matching bandwidth is 1.33 GHz (3.08-4.41 GHz), and its peak gain varies from 7 to 7.84 dB within the band. By placing the PRS superstrate above the antenna, gain further improves to 9.32 dBi without degrading the performance of the antenna. Measured results are presented to validate the antenna performance and results are compared against a large number of similarly available antenna.

Nonconventional metasurfaces: from non-Hermitian coupling, quantum interactions, to skin cloak

AbstractMetasurfaces are optically thin layers of subwavelength resonators that locally tailor the electromagnetic response at the nanoscale. Our metasurface research aims at developing novel designs and applications of metasurfaces that go beyond the classical regimes. In contrast to conventional phase gradient metasurfaces where each meta-atom responds individually, we are interested in developing metasurfaces where neighboring meta-atoms are strongly coupled. By engineering a non-Hermitian coupling between the meta-atoms, new degrees of freedom are introduced and novel functionalities can be achieved. We are also interested in combining classical metasurface with quantum emitters, which may offer opportunities for on-chip quantum technologies. Additionally, we have been designing metasurfaces to realize exciting phenomena and applications, such as ultrathin metasurface cloak and strong photonic spin-Hall effect. In this paper, we review our research efforts in optical metasurfaces in the past few years, which ranges from conventional to novel type of metasurface and from classical to quantum regime.

High-Efficiency and Full-Space Manipulation of Electromagnetic Wave Fronts with Metasurfaces

Metasurfaces offered great opportunities to control electromagnetic (EM) waves, but currently available meta-devices typically work either in pure reflection or pure transmission mode, leaving half of EM space completely unexplored. Here, we propose a new type of metasurface, composed by specifically designed meta-atoms with polarization-dependent transmission and reflection properties, to efficiently manipulate EM waves in the full space. As a proof of concept, three microwave meta-devices are designed, fabricated and experimentally characterized. The first two can bend or focus EM waves at different sides (i.e., transmission/reflection sides) of the metasurfaces depending on the incident polarization, while the third one changes from a wave bender for reflected wave to a focusing lens for transmitted wave as the excitation polarization is rotated, with all these functionalities exhibiting very high efficiencies (in the range of 85%-91%). Our findings significantly expand the capabilities of metasurfaces in controlling EM waves, and can stimulate high-performance multi-functional meta-devices facing more challenging and diversified application demands.

Basic Properties of Checkerboard Metasurfaces

This letter presents a new type of metasurface, which consists of a checkerboard-type layout, made of electrically small complementary metallic patches and apertures. Depending on whether the patches' vertices are interconnected or not, the structure may or may not support a propagating quasi-TEM mode. This feature offers the possibility of designing arbitrary transmission line paths on the checkerboard metasurface (CBMS) by dynamically changing the vertex connections. An equivalent network model is proposed for the CBMS transmission line and validated through simulated and experimental results. Furthermore, a preliminary experiment with a CBMS transmission line printed on a semiconductor substrate shows the possibility of reconfiguring the metasurface by photon injection.

Passive Lossless Huygens Metasurfaces for Conversion of Arbitrary Source Field to Directive Radiation

We present a semi-analytical formulation of the interaction between a given source field and a scalar Huygens metasurface (HMS), a recently introduced promising concept for wavefront manipulation based on a sheet of orthogonal electric and magnetic dipoles. Utilizing the equivalent surface impedance representation of these metasurfaces, we establish that an arbitrary source field can be converted into directive radiation via a passive lossless HMS if two physical conditions are met: local power conservation and local impedance equalization. Expressing the fields via their plane-wave spectrum and harnessing the slowly-varying envelope approximation we obtain semi-analytical formulae for the scattered fields, and prescribe the surface reactance required for the metasurface implementation. The resultant design procedure indicates that the local impedance equalization induces a Fresnel-like reflection, while local power conservation forms a radiating virtual aperture which follows the total excitation field magnitude. The semi-analytical predictions are verified by finite-element simulations of HMSs designed for different source configurations. Besides serving as a flexible design procedure for HMS radiators, the proposed formulation also provides a robust mechanism to incorporate a variety of source configurations into general HMS models, as well as physical insight on the conditions enabling purely reactive implementation of this novel type of metasurfaces.