Anomalous Reflection Research Articles

Simple Link-Budget Estimation Formulas for Channels Including Anomalous Reflectors

Reconfigurable intelligent surfaces (RIS) are a promising tool for optimization of propagation channels for advanced wireless communication systems. These tools are especially relevant for high-frequency (millimeter-band) links where directive antennas are used. RIS panels act as high-gain passive repeaters, whose reflected waves interfere with the waves reflected from the illuminated spots at supporting walls, creating a complex field pattern in the far zone. In this work, we consider a particular scenario of RIS for anomalous reflection and develop a simple link-budget model for non-line-of-sight channels via reflections from finite-size metasurfaces designed as anomalous reflectors or splitters. The developed model takes into account diffraction at the RIS panel edges as well as interference with reflections from supporting structures. We take into account realistic losses and confirm the validity of results by numerical simulations.

Broadband and high-efficiency thermal switchable InSb metasurface for terahertz wave anomalous reflection and focusing effect

In this paper, a reflective metasurface composed of a dielectric substrate sandwiched with a double-split-ring (DSR) structure InSb and a metal ground plane was proposed in terahertz (THz) region, which can realize a high-efficient thermal switchability of circular-polarization (CP) conversion, anomalous reflection, and planar reflective focusing effect in a broadband manner. Simulation results demonstrated that the designed InSb metasurface structure can achieve high-efficient reflective CP conversion, with the magnitude of the reflected orthogonal CP wave being over 0.8 on average from 0.7 THz to 1.55 THz under the external higher thermal (T = 320 K, “On” state). Conversely, the magnitude of the reflected orthogonal CP wave is nearly zero under external lower thermal conditions (T = 240 K, “Off” state). Furthermore, the proposed InSb metasurface structure can achieve a high-efficient reflective CP conversion with an efficiency of about 0.7 under the “On” state, and a 2π phase full coverage by adjusting the oriented rotation angle (α) of the DSR structure InSb. As evidences of the concept, two InSb metasurfaces have been constructed to achieve the broadband switchable anomalous reflection phenomenon and reflective focusing effect based on Pancharatnam-Berry (PB) phase principle. The proposed metasurface has great potential in developing a dynamically tunable device for THz wavefront modulation applications in the future.

Ge3Sb2Te6-based mid-infrared metasurfaces for polarization control and wavefront steering

Benefiting from excellent properties in wavefront control, germanium antimony telluride (GeSbTe)-based photonic devices provide new opportunities for manipulating electromagnetic wave. In this paper, Ge3Sb2Te6 meta-atoms are presented to realize polarization switching for mid-infrared wave through the state transition from the crystalline Ge3Sb2Te6 to the amorphous Ge3Sb2Te6. When the crystalline Ge3Sb2Te6 is involved, the proposed meta-atoms with 90° phase shift achieve high-efficiency polarization conversion and 360° phase coverage. As Ge3Sb2Te6 is changed to the amorphous state, phase coverage drops to only 36°, and most of the cross-polarized wave vanishes. Using these designed meta-atoms, three metasurfaces are implemented at 76.5 THz. Firstly, a gradient metasurface is constructed, and it dynamically switches between specular reflection and anomalous reflection. Next, a reflective metalens is proposed to realize switching between focusing and defocusing under different states of Ge3Sb2Te6. Lastly, a focused vortex beam is presented to reconstruct the mode of orbital angular momentum (OAM). All designs realize the switching between cross-polarization and co-polarization. Our work could have possible applications in fields such as mid-infrared switching, focusing, and wireless communication.

Reflections of High-Frequency Pulsed Ultrasound by Underwater Acoustic Metasurfaces Composed of Subwavelength Phase-Gradient Slits

We numerically and experimentally investigated the behavior of high-frequency underwater ultrasounds reflected by gradient acoustic metasurfaces. Metasurfaces were fabricated with a periodic array of gradient slits along the surface of a steel specimen. The finite element method was adopted for the acoustics–structure interaction problem to design the metasurfaces and simulate the reflected fields of the incident ultrasound. Our metasurfaces yielded anomalous reflection, specular reflection, apparent negative reflection, and radiation of surface-bounded modes for ultrasonic waves impinging on the metasurfaces at different incident angles. The occurrence of these reflection behaviors could be explained by the generalized Snell’s law for a gradient metasurface with periodic supercells. We showed that at some incident angles, strong anomalous reflection could be generated, which could lead to strong retroreflection at specific incident angles. Furthermore, we characterized the time evolution of the reflections using pulsed ultrasound. The simulated transient process revealed the formation of propagating reflected ultrasound fields. The experimentally measured reflected ultrasound signals verified the distinct reflection behaviors of the metasurfaces; strong anomalous reflection steering the ultrasound pulse and causing retroreflection was observed. This study paves the way for designing underwater acoustic metasurfaces for ultrasound imaging and caustic engineering applications using pulsed ultrasound in the high-frequency regime.

A two-dimensional grating surface made of quaternary Huygens elements excited by a real source

In this article, a new method to create an anomalous reflection in the desired direction is proposed. Two-dimensional grating surfaces consisting of four particles with the properties of a Huygens source are employed in each period. Then, this method is extended to the problem in which the grating surface is illuminated by a real source such as a horn. In this case, the designed grating surface has different periods in both directions to collimate the reflected wave and give an in-phase wavefront. Using our method, a high-efficiency reflectarray (RA) based on quaternary Huygens grating is designed. This RA is distinguished from common RAs due to its beam squint capability. This array offers more aperture efficiency and thus more gain in comparison to the leaky waves that inherently have low aperture efficiency. Therefore, our designed RA can compete with leaky wave antennas in many applications. The mentioned RA is designed to have the main beam in the direction of left( {{theta _0} = {{68}^{circ }},{varphi _0} = {{225}^{circ }}} right), at the frequency of 12 GHz. The simulation results show the realized gain and SLL of this antenna are 24.8 dB and -15.5 dB, respectively. Also, by changing the frequency in the range of 12–15 GHz, the direction of the main beam varies from left( {{{68}^{circ }}, {{225}^{circ }}} right) to left( {{{39}^{circ }}, {{225}^{circ }}} right).

RCS prediction and optimization for anomalous reflection metasurfaces using Floquet analysis

AbstractDue to their periodic nature, metasurfaces used to perform anomalous reflection raise parasitic harmonic reflections. We show a classical synthesis example of such a structure and highlight its limitations. Floquet analysis and its associated simulation environment are exploited to understand the origin of these parasitic reflections and to mitigate them. The proposed method is based on the optimization of the metasurface periodic pattern: the supercell. A predictive method is built to calculate radar cross-section patterns from supercell Floquet simulation, avoiding dealing with heavy simulations. The proposed model, the optimization outputs, and the general results are exposed in details. Different cases are also discussed to prove the repeatability of the proposed method. An earlier version of this paper was presented at the European Microwave Conference and was published in its proceedings.

Controlling solar radiation forces with graphene in plasmonic metasurface

Controlling and harvesting solar radiation pressure is a significant challenge, however, there are a few potential solutions, which are suitable for several key applications. In this study, an electrically tunable plasmonic metasurface is designed for the visible spectrum. Moreover, the normal and the tangential optical forces acting on the metasurface are calculated. Whilst presenting high efficiency in the anomalous reflection, the designed active metasurface provides tunability of optical forces acting on the metasurface. The metasurface is composed of tapered silver cells embedded on top of the graphene layer with 20 layers of graphene sheets. Hence, the transferred momentum to the metasurface can be controlled by tuning the Fermi level of graphene sheets. Our results can provide a suitable platform for optical force control desired in tunable radiation pressure harvesting, micro vehicles, solar sailing, and optical tweezers.

Anomalous non-Hermitian dynamical phenomenon on the quantum circuit

The anomalous non-Hermitian dynamical phenomenon with the non-Hermitian skin effect (NHSE) attracts wide attention due to its novel physics and promising applications. Here, we propose a new type of non-unitary discrete-time quantum walk system demonstrating the NHSE and anomalous non-Hermitian dynamical phenomena, including the dynamical chiral phenomenon, the funneling phenomenon on the domain wall, and the anomalous reflection on the phase impurity. Furthermore, we design the quantum circuit experiments of these quantum walk systems and numerically simulate them with quantum noises to verify the robustness of the non-Hermitian dynamical phenomenon on the noisy intermediate-scale quantum (NISQ) devices. Our work paves the way for implementing the non-Hermitian dynamical phenomenon on the quantum circuit.

Modes of gas migration and seepage on the salt-rooted Palmahim Disturbance, southeastern Mediterranean

Mass transport complexes often form key elements of petroleum systems, affecting sedimentary structures, seepage pathways and biodiversity hotspots on the seafloor. Yet, the feedback and interaction between these elements is not well constrained. This study investigates the modes of gas accumulation, migration, and seepage at the toe of Palmahim Disturbance (PD), a major salt-rooted mass transport complex across the southeastern Mediterranean margin, and adjacent edge of the eastern deep-sea fan of the Nile. Interpretation of a 3D time migrated seismic reflection dataset was calibrated with visual seafloor observations of active seepage. The toe of PD, in the eastern part of the study area, comprises four km-scale NE-SW oriented bathymetric ridges. At the crests of the eastern three of these ridges are six, hundreds-of-meters wide pockmark systems, four of which host verified seeps. Multiple sub-circular tens-of-meters wide pockmarks are mapped in the Nile fan west of PD. Active seepage was also identified within two elongate pockmarks along the flanks of the bordering Levant Channel. The seismic data reveal that the PD toe pockmarks and ridges overlie anomalous high amplitude seismic reflections (HASRs) from just beneath the surface to hundreds-of-meters deep intervals - below, at the base of and within a buried paleo mass transport deposit (MTD). These HASRs are interpreted to represent multiple gas-bearing intervals within thrust-faulted and folded blocks and their intermittent sealing, primarily at the base of the MTD. The Nile fan pockmarks overlie pervasive sub-seafloor HASRs that are overlain by low amplitude reflections, interpreted as gas-bearing channel-lobe sediments. Gas migration occurs via lateral to updip flow within depositional features and deeper folded sediments, and via sub-vertical flow, associated with the formation and leakage of transient reservoirs. Extension of fan sediments towards the PD pockmarks suggests additional updip focusing of gas, complementing sub-vertical gas flow to the PD pockmarks.

Spin‐Selective Absorption and Geometric‐Phase Modulation via Chiral Metasurface in Triple Bands

AbstractMetasurfaces with spin‐selective reflection or transmission functions for circularly‐polarized (CP) incident waves have aroused researchers' great attention. However, current spin‐selective metasurface designs have yet to mature into a practical method due to the limitations of single operating band or inefficient phase modulation. Herein, a novel chiral meta‐atom is proposed, exhibiting spin‐selective absorption/reflection functions for dual‐orthogonal CP incident waves at three different operating bands. More significantly, the Pancharatnam–Berry phase theory is introduced at all working frequencies to generate a full 2π reflection phase modulation by rotating the chiral resonator, and the three distinct absorption bands remain almost constant with the rotation. Theoretical results indicate that high absorption can separately act on left‐handed or right‐handed CP incident waves at triple bands, and meanwhile, the other incident wave with different handedness is efficiently reflected without changing the handedness. As a proof of concept, two tri‐band meta‐devices with spin‐selective anomalous reflection and spin‐selective orbital angular momentum generating functions are designed and experimentally characterized, both of which exhibit excellent spin‐dependent bi‐functional performances at three different operating bands. The research results provide a promising route to realize spin‐selective meta‐devices with multi‐band operating modes in wireless communication systems and multispectral imaging and information encryption fields.

Terahertz Silicon Metagratings: High‐Efficiency Dispersive Beam Manipulation above Diffraction Cone

AbstractOptical wavefront engineering is essential for the development of next‐generation integrated photonic devices. It is used for reflecting terahertz waves in a predesigned nonspecular direction with near‐unitary efficiency, which is a longstanding challenge for high‐performance functional devices. Recently, metagratings have offered an efficient solution for beam steering at large angles without the need for a discretization phase or impedance profile. Here, all‐dielectric metagratings fabricated using a silicon cuboid complex lattice are proposed and demonstrated experimentally to achieve anomalous terahertz beam reflections above the diffraction cone with unitary diffraction efficiency. For the bipartite metagrating system, a single dispersive scatterer per unit is effective for achieving broadband beam steering because of Brillouin zone folding, and another perturbative synergetic scatterer is introduced to slightly tailor the array coupling and improve the performance. High‐efficiency beam steering, including both retroreflection under oblique incidence and one‐way diffraction under normal incidence, can be achieved by breaking structural symmetry and coherently suppressing unnecessary radiation channels. Moreover, silicon metagratings with spatially dispersive response features show perfect anomalous reflection operation in the broadband region, which is promising for leveraging terahertz spatially separated devices.

Super-reflector enabled by non-interleaved spin-momentum-multiplexed metasurface

Electromagnetic wave multiplexing, especially for that occurring at different incidences (spatial-frequency multiplexing), is pivotal for ultrathin multifunctional interfaces and high-capacity information processing and communication. It is yet extremely challenging based on passive and compact wave elements, since the wave excitation and scattering channels are exclusively coupled through gradient phases and hence momentum matching condition at the interface. Here, we propose a spin-momentum multiplexed paradigm called a super-reflector enabling on-demand control of both retroreflections and anomalous reflections using a non-interleaved single-celled metasurface. By multiplexing four channels connecting two spin states excited onto each input of three spatial frequencies, a total of twelve channels are engineered, among which three are retroreflected channels and the residual are anomalous reflection ones. Our compound multiplexed super-reflector allows five degrees of freedom in circular polarization Jones' matrix, approaching the intrinsic upper limit of such planar metasurface. The concept has been experimentally verified by a proof-of-concept super-reflector at microwave frequency, showcasing twelve reflected beams and a high efficiency exceeding 90.6% defined as the ratio of reflected power to incidence for each channel beam. Our strategy opens a new avenue for angle multiplexing and angle-resolved metadevices toward the capacity limit of 2D planar Jones’ matrix.

Optical metasurfaces for multiplex high-performance grating-type structural colors.

Optical metasurfaces provide a significant approach for the production of structural colors due to their excellent optical control abilities. Herein, we propose trapezoidal structural metasurfaces for achieving multiplex grating-type structural colors with high comprehensive performance originating from the anomalous reflection dispersion in the visible band. Single trapezoidal metasurfaces with different x-direction periods can tune the angular dispersion regularly from 0.036 rad/nm to 0.224 rad/nm to generate various structural colors, and composite trapezoidal metasurfaces with three kinds of combinations can achieve multiplex sets of structural colors. The brightness can be controlled by adjusting the distance between the trapezoids in a pair accurately. The designed structural colors have higher saturation than traditional pigmentary colors, whose excitation purity can reach 1.00. The gamut is about 158.1% of the Adobe RGB standard. This research has application potential in ultrafine displays, information encryption, optical storage, and anti-counterfeit tagging.

A Multihop Strategy for the Planning of EM Skins in a Smart Electromagnetic Environment

This article deals with the electromagnetic (EM) planning of static and passive EM skins (EMSs) in complex urban scenarios to improve the EM coverage of the base-station (BTS) antenna by means of a set of multihop (MH) cascaded reflections. Toward this end, an innovative system-by-design (SbD)-based method is developed where wireless links of arbitrary “depth,” which are implemented through multiple anomalous cascaded reflections, are optimized. Representative numerical results, concerned with real-world scenarios, are analyzed to assess the capabilities and the potentialities of such an instance of the so- called smart EM environment (SEME).

Deterministic approach to design passive anomalous-diffraction metasurfaces with nearly 100% efficiency

Abstract Designing perfect anomalous reflectors is crucial for achieving many metasurface-based applications, but available design approaches for the cases of extremely large bending angles either require unrealistic gain–loss materials or rely on brute-force optimizations lacking physical guidance. Here, we propose a deterministic approach to design passive metasurfaces that can reflect impinging light to arbitrary nonspecular directions with almost 100% efficiencies. With both incident and out-going far-field waves given, we can retrieve the surface-impedance profile of the target metadevice by matching boundary conditions with all allowed near-field modes added self-consistently and then construct the metadevices deterministically based on passive meta-atoms exhibiting local responses. We design/fabricate two proof-of-concept microwave metadevices and experimentally demonstrate that the first one achieves anomalous reflection to a 70° angle with efficiency ∼98%, and the second one can generate multiple reflected beams with desired bending angles and power allocations. Our findings pave the way for realizing high-efficiency wave-control metadevices with desired functionalities.

Controls on shallow gas distribution, migration, and associated geohazards in the Yangtze subaqueous delta and the Hangzhou Bay

Shallow gas is generally extensively distributed in the Holocene muddy sediments and gas seepage has been increasingly reported to induce geohazards in coastal seas, but controls on gas distribution and migration remain elusive. This study explores gas distribution and migration in the Yangtze subaqueous delta and the Hangzhou Bay using high-resolution acoustic profiles and core data. Shallow gas is widely detected by the common presence of acoustic anomalous reflections including enhanced reflection, gas chimney, bright spot, acoustic blanking, and acoustic turbidity. The gas front depth is generally less than 17.5 m, and is meanly shallower in the Hangzhou Bay than in the Yangtze subaqueous delta because of relatively shallower water depth and coarser Holocene sediments in the Hangzhou Bay. Shallow gas is inferred to be a biogenic product, and its distribution is highly contingent on the Holocene stratal thickness and water depth. Active gas migration and seepages are evident, and recently increasing occurrences of gas seepage can be ascribed to global warming and seabed erosion due to sediment deficit. The findings warn us to pay more attention to the positive feedback loops of gas seepages with global warming and seabed erosion for the associated geohazard prediction and reduction, typically in the highly developed coastal regions.

Anomalous reflection with customized high-efficiency bandwidth.

Anomalous reflection from metasurfaces with 100% efficiency at optical frequencies was not achieved until an all-dielectric quasi-three-dimensional subwavelength structure was proposed. The desired nonlocal control of light waves is realized by designing phase responses of multilayer films at a single wavelength. However, a high-efficiency bandwidth is not controllable by designing only the phase response at a single wavelength. Here, we propose the use of a multilayer metasurface to achieve anomalous reflection with a customized high-efficiency bandwidth. The interference of the successive light waves scattered from the structure at multiple wavelengths is controlled by phase dispersion regulation of multilayer films. As a proof of concept, two sets of multilayer films with different phase dispersions were designed to realize broadband (∼110 nm) and narrowband (∼15 nm) anomalous reflections, both with an efficiency of over 80%. The results offer a general strategy to design high-efficiency anomalous reflection with arbitrary bandwidth and might stimulate various potential applications for metadevices.

Inverse design of broadband acoustic metasurfaces for reflective wavefront modulation through the topology optimization method

The design of broadband acoustic metasurfaces is an important research challenge. Topology optimization with a genetic algorithm (TOGA) is used in this paper to design a set of reflection acoustic metasurfaces with discrete phase shift characteristics. This method allows the design of selective single-frequency and broadband metasurfaces. First, nine metasurface units are designed with a total phase gradient of 2π at 3500 Hz. Simulations and experiments verify the anomalous reflection phenomenon of the metasurface in the reflected sound field and achieve wave focusing and self-bending functions by adjusting the position distribution of the units. Compared with single-frequency optimization studies, broadband acoustic metasurface units are designed with a linear phase dispersion in the range of 2000–5000 Hz, which achieves anomalous reflection with the same reflection angle and acoustic focusing phenomenon under broadband incident sound conditions. The ability of the algorithm to modulate the acoustic phase dispersion and the potential mechanism of generating different phase differences are further investigated. This method provides more accurate phase controllability for broadband acoustic metasurface optimization design and provides some ideas for the design of broadband structures in related fields.

Manipulating mid-infrared wavefront through reflective Ge3Sb2Te6 metasurfaces

Due to the increasing complexity of modern communication systems, the requirements for electromagnetic wave are becoming more and more rigorous. Traditional natural materials are not easy to integrate into tunable systems. Metasurface is a two-dimensional array, and it has a more significant advantage in electromagnetic control and attracts great attention. Here, Ge3Sb2Te6-based metasurfaces are presented to control electromagnetic wavefront by changing the state of Ge3Sb2Te6 in the mid-infrared range. Eight meta-atoms are designed to form linear phase distribution with phase difference of 45° at 74 THz. When Ge3Sb2Te6 is in the amorphous state, the designed meta-atoms have low loss and high reflection. Ge3Sb2Te6 block is designed into a specific structure in a certain way, which realizes deflection of electromagnetic wavefront and vortex beam with orbital angular momentum l = 1 or l = 2. By means of convolution, anomalous reflection is combined with orbital angular momentum to form an anomalously deflected vortex beam. When the state of Ge3Sb2Te6 is crystalline, amplitudes of meta-atoms decrease and linear phase distribution is destroyed. Reflected wave becomes almost mirror reflection wave. Our design may open a pathway to novel types of metasurfaces.

Anomalous Reflection From a Phase Gradient Metasurface With Arbitrary Incident Angle

A planar phase gradient metasurface (PGM) with phase gradients in two in-plane directions will introduce two additional wave vectors to the reflected wave vector. For small incident angles, close to the normal vector, the magnitude of the reflected wave vector is smaller than that of the incident wave vector and the direction of the anomalous reflected wave can be determined from the incident wave vector components and additional phase gradient components. The expanded generalized Snell’s law, which includes diffraction order modes, is combined with array theory to accurately predict the directions of the reflected waves from a planar PGM for incident angles where the magnitude of the reflected wave vector is larger than that of the incident wave vector. The predicted directions of the reflected waves from a planar PGM are compared with simulated RCS results obtained with CST Studio Suite and measured results obtained in a compact range.