Huygens' metasurfaces have demonstrated a remarkable potential to perform wave transformations within a subwavelength region. In particular, omega-bianisotropic Huygens' metasurfaces have allowed for the passive implementation of any wave transformation that conserves real power locally. Previous reports have also shown that Huygens' metasurface pairs are capable of realizing transformations that break the local power conservation requirement by redistributing the total power, while the wave propagates between the two metasurfaces. However, the required separation distance overshadows the low-profile characteristics of the individual metasurfaces and leads to bulky designs, especially for lower frequencies. In this work, we develop a method of designing omega-bianisotropic Huygens' metasurface pairs, relying on a point-matching process of the real power at the two metasurfaces. We highlight the versatility of our method by presenting two variations of the configuration, depending on whether the electromagnetic source is located within or outside the metasurface pair. Based on the examples of a cylindrical-wave to plane-wave transformation and a beam expander, we examine the impact of multiple reflections, as a way to overcome the size limitations and design compact structures. Moreover, we explore possible beamforming applications through an example of a Taylor-pattern antenna with a single feed-point between the two metasurfaces.
This work investigates the generation of arbitrary electromagnetic waveforms inside a geometrical area enclosed by an active metasurface. We introduce the contraption of the Huygens' box, where a region of space is enclosed by an active Huygens' metasurface. We show that, upon generating the necessary electric and magnetic currents, we can create any desired electromagnetic field inside the Huygens' box. Using this method, we demonstrate through simulation and experiment the generation of travelling plane waves, a standing plane wave and a Bessel wave inside a metallic cavity. By linear superp…
Huygens' metasurfaces have demonstrated the ability to tailor electromagnetic wavefronts with passive low-profile structures. The fundamental constraint enabling passive and ideally lossless solutions is the conservation of the normal real power locally along the metasurface. In this work, we examine the use of auxiliary surface waves to overcome this limitation and design Huygens' metasurfaces for wave transformations with different incident and output power density profiles. The developed method relies on the optimization of a surface-wave distribution that is utilized to redistribute the po…
This paper investigates the discretization of a periodic metasurface and demonstrates how such a surface can achieve perfect anomalous reflection. Whilst most contemporary theoretical works on metasurfaces deal with continuous current or impedance distributions, we examine how discretization affects a metasurface, and show that in some cases one can discretize a metasurface aggressively --- to the extent of having only two cells per spatial period. Such aggressive discretization can lead to great simplifications in metasurface design, and perhaps more surprisingly, a possible performance impro…
Huygens' metasurfaces are electrically thin devices which allow arbitrary field transformations. Beam refraction is among the first demonstrations of realized metasurfaces. As previously shown for extreme-angle refraction, control over only the electric impedance and magnetic admittance of the Huygens' metasurface proved insufficient to produce the desired reflectionless field transformation. To maintain zero reflections for wide refraction angles, magnetoelectric coupling between the electric and magnetic response of the metasurface, leading to bianisotropy, can be introduced. In this paper, …
In this paper we propose a new metasurface that is able to reflect a known incoming electromagnetic wave into an arbitrary direction, with perfect power efficiency. This seemingly simple task, which we hereafter call perfect anomalous reflection, is actually highly non-trivial due to the differing wave impedances and complex interference between the incident and reflected waves. Heretofore, proposed metasurfaces which achieve perfect anomalous reflection require complicated, deeply subwavelength and/or multilayer element structures which allow them to couple to and from leaky and/or evanescent…
In this paper, a novel concept of a leaky-wave antenna is proposed, based on the use of Huygens' metasurfaces. It consists of a parallel-plate waveguide in which the top plate is replaced by a bianisotropic metasurface of the Omega type. It is shown that there is an exact solution to transform the guided mode into a leaky-mode with arbitrary control of the constant leakage factor and the pointing direction. Although the solution turns out to be periodic, only one Floquet mode is excited and radiates, even for electrically long periods. Thanks to the intrinsic spurious Floquet mode suppression,…
Recently, a special class of Huygens' surfaces has been proposed which are capable of manipulation of transmitted wavefronts while exhibiting high transparency over a broad range of frequencies. In this work we propose and study a new meta-atom for achieving broadband transparency of Huygens' surfaces based on two mutually shifted split-ring resonators. The resonators were carefully optimized using a new developed analytical model so that their electric and magnetic responses was balanced to achieve unidirectional scattering of the incident field. Moreover, their mutual shift canceled their in…
Metasurfaces are an enabling technology for complex wave manipulation functions, including in the terahertz frequency range, where they are expected to advance security, imaging, sensing, and communications technology. For operation in transmission, Huygens' metasurfaces are commonly used, since their good impedance match to the surrounding media minimizes reflections and maximizes transmission. Recent theoretical work has shown that Huygens' metasurfaces are non-optimal, particularly for large angles of refraction, and that to eliminate reflections and spurious diffracted beams it is necessar…
Recent metasurface developments have led to their consideration for extending the angular scan range of phased arrays. This paper considers the use of Huygens' metasurfaces as lenses to accomplish the task. Ray optics is used to uncover how a single lens can extend the scan range. It is shown that a single scan extending lens leads to a broadside directivity degradation of the original beam. This directivity degradation is quantitatively characterized as a function of the desired angular scan-range expansion. A method of simulating phase boundaries is presented and used to verify the theoretic…
Metasurfaces composed of subwavelength unit cells usually require a large number of unit cells which leads to complicated design and optimization. Aggressive discretization in a metasurface can significantly reduce the number of unit cells within a period, resulting in lower requirement for phase and/or surface impedance coverage. Additionally, the enlarged unit cells will encounter negligible mutual couplings when combined together, hence making straightforward the process of metasurface design. These advantages combine to allow the design of a novel class of metasurfaces which support the hi…
Over the past decades, many radome designs to extend the angular scan range of phased-array antennas have been devised by utilizing dielectric materials and metamaterials. More recently, metasurface technology such as planar lenses and beam deflectors have been applied to phased arrays, enabling scan-angle enhancers to have a low profile. In this work, a physical Huygens' metasurface (HMS) two-lens system for scanangle doubling of a phased array is presented. For the HMS unit cells, the wire-loop topology is deployed to achieve high transmission for the required phase-angle shift. The proposed…
Zhejiang Key Laboratory of 3D Micro/Nano Fabrication and Characterization, Department of Electronic Science and Engineering, School of Engineering, Westlake University（西湖大学工程学院电子科学与工程系三维微纳加工与表征浙江省重点实验室）；Westlake Center for Micro/Nano Fabrication, Westlake University（西湖大学微纳加工中心）；Eastern Institute of Technology（宁波东方理工大学）
Realization of the anomalous refraction effects predicted by Huygens' metasurfaces (HMS) have required tedious and time-consuming trial-and-error numerical full-wave computations. It is shown herein that these requirements can be alleviated for transverse magnetic (TM) propagation by a periodic dielectric-based HMS consisting of an electrically thick array of cascaded Fabry-Pérot etalons. This "Fabry-Pérot HMS" (FP-HMS) is easily designed to mimic the local scattering coefficients of a standard zero-thickness HMS (ZT-HMS) which, according to homogenization theory, should result in the desired …
Harnessing Selective State Space Models to Enhance Semianalytical Design of Fabrication-Ready Multilayered Huygens' Metasurfaces: Part I - Field-based Semianalytical Synthesis
Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering, Technion（安德鲁和埃尔纳·维特比电气与计算机工程学院，以色列理工学院）；Faculty of Electrical and Computer Engineering, Tel-Aviv University（电气与计算机工程学院，特拉维夫大学）；Reykjavik University（雷克雅未克大学）
Huygens' metasurfaces have demonstrated almost arbitrary control over the shape of a scattered beam, however, its spatial profile is typically fixed at fabrication time. Dynamic reconfiguration of this beam profile with tunable elements remains challenging, due to the need to maintain the Huygens' condition across the tuning range. In this work, we experimentally demonstrate that a time-varying metadevice which performs frequency conversion can steer transmitted or reflected beams in an almost arbitrary manner, with fully dynamic control. Our time-varying Huygens' metadevice is made of both el…
A metasurface particle with independent transmission and reflection full phase coverage for circularly polarized waves is introduced. This particle is constituted of two parts, one controlling the power splitting and the reflection phase, and the other one controlling the transmission phase, both leveraging the Pancharatnam-Berry phase principle. Given its unique flexibility, this particle may find various applications in metasurface technology.
As 2D materials with subwavelength structures, elastic metasurfaces show remarkable abilities to manipulate elastic waves at will through artificial boundary conditions. However, the application prospects of current metasurfaces may be restricted by their phase-only modulating boundaries. Herein, we present the next generation of elastic metasurfaces by additionally incorporating amplitude-shift modulation. A general theory for target wave fields steered by metasurfaces is proposed by modifying the Huygens-Fresnel principle. As examples, two amplitude-shift metasurfaces concerning flexural wav…
Harnessing Selective State Space Models to Enhance Semianalytical Design of Fabrication-Ready Multilayered Huygens' Metasurfaces: Part II - Generative Inverse Design (MetaMamba)
Tel Aviv University（特拉维夫大学）；Technion – Israel Institute of Technology（以色列理工学院）
We demonstrate tunable perfect anomalous reflection with metasurfaces incorporating lumped elements. The tunable capacitance of each element provides continuous control over the local surface reactance, allowing for controlling the evanescent field distribution and efficiently tilting the reflected wavefront away from the specular direction. The performance of the metasurface is evaluated for both TE and TM polarization and for reflection to the first and second diffraction order.
Metasurfaces impart phase discontinuities on impinging electromagnetic waves that are typically limited to 0-2$π$. Here, we show that they can break free from this limitation and supply arbitrarily-large phase modulation over ultra-wide bandwidths. This is achieved by implementing multiple, properly-arranged resonances in the electric and magnetic sheet admittivities. We demonstrate metasurfaces that can perfectly reflect a broadband pulse imparting a prescribed group delay without distorting the pulse shape, opening new possibilities for temporal control and dispersion engineering across deep…
Previous research has attempted to minimize the influence of loss in reflection- and transmission-type acoustic metasurfaces. This letter shows that, by treating the acoustic metasurface as a non-Hermitian system and by harnessing loss, unconventional wave behaviors that do not exist in lossless metasurfaces can be uncovered. Specifically, we theoretically and experimentally demonstrate a non-Hermitian acoustic metasurface mirror featuring extremely asymmetrical reflection at the exception point. As an example, the metasurface mirror is designed to have high-efficiency retro-reflection when th…
This letter presents the concept of Total Internal Reflection metasurface (TIR-MS) which supports the realization of structure-embedded subwavelength acoustic shields for elastic waves propagating in thin waveguides. The proposed metasurface design exploits extreme phase gradients, implemented via locally resonant elements, in order to achieve operating conditions that are largely beyond the critical angle. Such artificial discontinuity is capable of producing complete reflection of the incoming waves regardless of the specific angle of incidence. From a practical perspective, the TIR-MS behav…
Electromagnetic metasurfaces can be characterized as intelligent if they are able to perform multiple tunable functions, with the desired response being controlled by a computer influencing the individual electromagnetic properties of each metasurface inclusion. In this paper, we present an example of an intelligent metasurface which operates in the reflection mode in the microwave frequency range. We numerically show that without changing the main body of the metasurface we can achieve tunable perfect absorption and tunable anomalous reflection. The tunability features can be implemented usin…
Metasurface with gradient phase response offers new alternative for steering the propagation of waves. Conventional Snell's law has been revised by taking the contribution of local phase gradient into account. However, the requirement of momentum matching along the metasurface sets its nontrivial beam manipulation functionality within a limited-angle incidence. In this work, we theoretically and experimentally demonstrate that the acoustic gradient metasurface supports the negative reflection for all-angle incidence. The mode expansion theory is developed to help understand how the gradient me…
In this paper, a wideband and low-scattering metasurface in terahertz (THz) is introduced. The proposed coding metasurface is composed of four different graphene square patches in one layer, which has a distinct bias voltage. By optimizing the chemical potential of each patch, the reflection phase and amplitude of a designed element can be controlled in a real-time manner. The chemical potential optimizing approach is a promising method to develop metasurfaces, which can tune the reflection phase, magnitude, or polarization dynamically at different frequencies spectrum. Indeed, by adjusting th…
Beyond the scope of space-coding metasurfaces, space-time digital metasurfaces can substantially expand the application scope of digital metamaterials in which simultaneous manipulation of electromagnetic waves in both space and frequency domains would be feasible. In this paper, by adopting a superposition operation of terms with unequal coefficient, Huygens principle, and a proper time-varying biasing mechanism, some useful closed-form formulas in the class of large digital metasurfaces were presented for predicting the absolute directivity of scatted beams. Moreover, in the harmonic beam st…
In this study, we demonstrate first, to the best of our knowledge, robust and dynamically polarization-controlled tunable-high-Q PIT in designed nanostructures metasurface, whose sharp resonance is guaranteed by design and protected against large geometrical imperfections. By employing the explicit analysis of near-field characteristic in the reciprocal-space based on the momentum matching, and the far-field radiation features with point-scattering approach in real-space sparked from Huygens's principles, the physics of interference resonance in the spectra for plane-wave optical transmission …
The unusual viscoelastic properties of silica aerogel plates are efficiently used to design subwavelength perfect sound absorbers. We theoretically, numerically and experimentally report a perfect absorbing metamaterial panel made of periodically arranged resonant building blocks consisting of a slit loaded by a clamped aerogel plate backed by a closed cavity. The impedance matching condition is analyzed using the Argand diagram of the reflection coefficient, i.e., the trajectory of the reflection coefficient as a function of frequency in the complex plane. The lack or excess of losses in the …
We consider reciprocal metasurfaces with engineered reflection and transmission coefficients and study the role of normal (with respect to the metasurface plane) electric and magnetic polarizations on the possibilities to shape the reflection and transmission responses. We demonstrate in general and on a representative example that the presence of normal components of the polarization vectors does not add extra degrees of freedom in engineering the reflection and transmission characteristics of metasurfaces. Furthermore, we discuss advantages and disadvantages of equivalent volumetric and full…
Compact, lightweight and high-performance spatial light modulators (SLMs) are crucial for modern optical technologies. The drive for pixel miniaturization, necessary to improve their performance, has led to a promising alternative, active optical metasurfaces, which enable tunable subwavelength wavefront manipulation. Here, we demonstrate an all-solid-state programmable transmissive SLM device based on Huygens dielectric metasurfaces. The metasurface features electrical tunability, provided by mature liquid crystals (LCs) technology. In contrast to conventional LC SLMs, our device enables high…
Lead halide perovskites (MAPbX3) are known to have high refractive index and controllable bandgap, making them attractive for all-dielectric and tunable metasurfaces. Till now, perovskite metasurfaces have only been used in structural colors. More interesting meta-devices with 2π phase control are still absent. Here we experimentally demonstrate the MAPbX3 perovskite based metasurfaces with a complete control of phase shift in a reflection mode. By utilizing MAPbBr3 cut-wires as meta-atoms on a ground metal film, we find that the MAPbBr3 perovskite metasurface can produce full phase control fr…
The strong interaction of light with micro- and nanostructures plays a critical role in optical sensing, nonlinear optics, active optical devices, and quantum optics. However, for wavefront shaping, the required local control over light at a subwavelength scale limits this interaction, typically leading to low-quality-factor optical devices. Here, we demonstrate an avenue towards high-quality-factor wavefront shaping in two spatial dimensions based on all-dielectric Huygens metasurfaces by leveraging higher-order Mie resonances. We design and experimentally realize transmissive band stop filte…
Metasurfaces with planar profile and wave front shaping capabilities would be ideally suitable to improve the performance of acoustic wave-based applications. It is significant that the general Snell's law provides a new approach to engineer the phase profile of reflected acoustic wave. Here, we present a new type of acoustic metasurface based on three-component composites which contain a steel ball coated with a thin elliptical layer of silicone rubber and embedded in epoxy. The acoustic metasurface with changeable radii of steel balls can realize the anomalous reflections, a planar acoustic …
We present an analytical scheme for the design of realistic metagratings for wide-angle engineered reflection. These recently proposed planar structures can reflect an incident plane wave into a prescribed (generally non-specular) angle with very high efficiencies, using only a single meta-atom per period. Such devices offer a means to overcome the implementation difficulties associated with standard metasurfaces (consisting of closely-packed subwavelength meta-atoms) and the relatively low efficiencies of gradient metasurfaces. In contrast to previous work, in which accurate systematic design…
Vortex beams carrying orbital angular momentum are extensively studied owing to its potential to expand channel capacity of microwave and optical communication. By utilizing the Pancharatnam-Berry phase concept, an ultra-wideband single layer metasurface is proposed to realize the conversion from incident plane waves to reflected vortex beams covering a considerable bandwidth from 6.75 to 21.85 GHz . An equivalent circuit model combined with broadband phase shift network is developed to effectively design the meta-atoms in metasurface. It is the first time to design wideband metasurfaces with …
Meta-optics based on optically-resonant dielectric nanostructures is a rapidly developing research field with many potential applications. Halide perovskite metasurfaces emerged recently as a novel platform for meta-optics, and they offer unique opportunities for control of light in optoelectronic devices. Here we employ the generalized Kerker conditions to overlap electric and magnetic Mie resonances in each meta-atom of MAPbBr3 perovskite metasurface and demonstrate broadband suppression of reflection down to 4%. We reveal also that metasurface nanostructuring is also beneficial for the enha…
Functional tunability, environmental adaptability, and easy fabrication are highly desired properties in metasurfaces. Here we provide a tunable bilayer metasurface composed of two stacked identical dielectric magnetic mirrors, which are excited by the dominant electric dipole and other magnetic multipoles, exhibiting nonlocal electric field enhancement near the interface and high reflection. Differ from the tunability through the direct superposition of two structures with different functionalities, we achieve the reversible conversion between high reflection and high transmission by manipula…
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 d…
Optical metasurfaces have been extensively investigated, demonstrating diverse and multiple functionalities with complete control over the transmitted and reflected fields. Most optical metasurfaces are however static, with only a few configurations offering (rather limited) electrical control, thereby jeopardizing their application prospects in emerging flat optics technologies. Here, we suggest an approach to realize electrically tunable optical metasurfaces, demonstrating dynamic Fresnel lens focusing. The active Fresnel lens (AFL) exploits the electro-optic Pockels effect in a 300-nm-thick…
Omega bianisotropic metasurfaces (OBMS) provide wave-control capabilities not previously available with Huygens' metasurfaces (HMS). These enhanced capabilities derive from the additional degree of freedom provided by OBMS, and are based on analyses of zero-thickness surfaces with abstract surface impedance properties. However, the design of practical metasurfaces has proven tedious. Herein, we propose a novel, easily designed structure to realize OBMSs. Extending our previous work, we show that an asymmetrical cascade of two judiciously engineered Fabry-Perot (FP) etalons could form an OBMS m…
In view of extremely challenging requirements on design and optimization of future mobile communication systems, researchers are considering possibilities of creation intelligent radio environments by using reconfigurable and smart metasurfaces integrated into walls, ceilings, or facades. In this novel communication paradigm, tunable metasurfaces redirect incident waves into the desired directions. In order to design and characterize such smart radio environments in any realistic scenario, it is necessary to know how these metasurfaces behave when illuminated from other directions and how scat…
