Metamaterials are composed of periodic subwavelength metal/dielectric structures that resonantly couple to the electric and/or magnetic components of the incident electromagnetic fields, exhibiting ...properties that are not found in nature. This class of micro- and nano-structured artificial media have attracted great interest during the past 15 years and yielded ground-breaking electromagnetic and photonic phenomena. However, the high losses and strong dispersion associated with the resonant responses and the use of metallic structures, as well as the difficulty in fabricating the micro- and nanoscale 3D structures, have hindered practical applications of metamaterials. Planar metamaterials with subwavelength thickness, or metasurfaces, consisting of single-layer or few-layer stacks of planar structures, can be readily fabricated using lithography and nanoprinting methods, and the ultrathin thickness in the wave propagation direction can greatly suppress the undesirable losses. Metasurfaces enable a spatially varying optical response (e.g. scattering amplitude, phase, and polarization), mold optical wavefronts into shapes that can be designed at will, and facilitate the integration of functional materials to accomplish active control and greatly enhanced nonlinear response. This paper reviews recent progress in the physics of metasurfaces operating at wavelengths ranging from microwave to visible. We provide an overview of key metasurface concepts such as anomalous reflection and refraction, and introduce metasurfaces based on the Pancharatnam-Berry phase and Huygens' metasurfaces, as well as their use in wavefront shaping and beam forming applications, followed by a discussion of polarization conversion in few-layer metasurfaces and their related properties. An overview of dielectric metasurfaces reveals their ability to realize unique functionalities coupled with Mie resonances and their low ohmic losses. We also describe metasurfaces for wave guidance and radiation control, as well as active and nonlinear metasurfaces. Finally, we conclude by providing our opinions of opportunities and challenges in this rapidly developing research field.
Optically transparent metamaterial microwave absorbers (MMAs) developed so far unexceptionally encounter an intrinsic contradiction between extending the absorption bandwidth and improving optical ...transparency, hindering their practical applications. This work, in its experiment and calculation, demonstrates an MMA with both broadband microwave absorption and excellent optical transparency by standing‐up closed‐ring resonators (CRRs) in an indium tin oxide backed Plexiglas board. The as‐designed MMA shows a strong microwave absorption of 85% covering a wide frequency of 5.5–19.7 and 22.5–27.5 GHz up to a large incident angle of 70o due to the electric and magnetic resonances caused by the standing‐up arrangement of the CRRs, as well as the multiple reflection mechanism. Moreover, in sharp contrast to the widely adopted stacking multiple layers at the expense of greatly reduced optical transparency, it has an optical transmittance of around 82%, as calculated by a transfer matrix method. The standing‐up MMA proposed here provides an effective way to achieve broadband microwave absorption and high compatibility with optical transparency, enabling wide applications in window glass of stealth armament and electromagnetic compatible buildings/facilities.
An optically transparent metamaterial absorber, obtained by standing closed‐ring resonators in an indium tin oxide backed Plexiglas board, demonstrates both a bandwidth for 90% microwave absorption exceeding 14 GHz and an average optical transmittance of 82% due to the simultaneous excitement of electric and magnetic resonances, as well as the multiple reflections.
Reconfigurable intelligent surfaces (RIS) have been recently introduced to optical wireless communication (OWC) networks to resolve skip areas and improve the signal-to-noise ratio at the user's end. ...In OWC networks, RIS are based on mirrors or metasurfaces. Metasurfaces have evolved significantly over the last few years. As a result, coding, digital, programmable, and information metamaterials have been developed. The advantage of these materials is that they can enable digital signal processing (DSP) techniques. For the first time, this paper proposes the use of digital RIS (DRIS) in OWC systems. We discuss the concept of DRIS and the application of DSP methods to the physical material. In addition, we examine metamaterials for optical DRIS with liquid crystals serving as the front row material. Finally, we present a design example and discuss future research directions.
Auxetic mechanical metamaterials (AMMs), as an exciting paradigm of metamaterials, have attracted increasing attention due to their interesting mechanical properties (e.g. negative Poisson's ratio), ...as well as the emergence of advanced manufacturing technology (e.g. 3D printing). Although various reviews on AMMs, their structures, properties, and applications, have existed, it still lacks a comprehensive review in terms of manufacturing methods. Herein, the latest progress in AMMs is extensively reviewed, including AMMs’ structures, characteristics, manufacturing methods, and applications. In addition, the current challenges and future works of AMMs are concluded and discussed. This Review aims to serve as a collection of knowledge that supplies more comprehensive understanding and inspiration to support further developments of AMMs from the perspective of design and manufacturing.
Herein, the recent advancements in auxetic mechanical metamaterials (AMMs) are systematically reviewed, including AMMs’ structures, characteristics, manufacturing methods, and applications. Further, the current challenges and future works of AMMs are discussed in terms of the above aspects. This Review provides a collection of knowledge that promotes the further developments of AMMs.
•A graded metamaterial beam is proposed for realizing broadband vibration suppression.•The spectral element method (SEM) is used to model the graded metamaterial beam.•Several figures of merit are ...developed for a quantitative analysis.•Criteria towards the tuning of the frequency spacing between local resonators are derived.•A practical implementation of the proposed graded metamaterial beam is demonstrated.
This paper investigates a technique for broadband vibration suppression using a graded metamaterial beam. A series of local resonators with the same mass but different natural frequencies are attached to the beam. The difference between the natural frequencies of neighboring local resonators is defined as the frequency spacing. The spectral element method (SEM) is used to model the graded metamaterial beam, and is verified by the corresponding finite element model (FEM). Three figures of merit are defined to quantitatively evaluate the vibration suppression performance of the proposed metamaterial beam, in terms of the attenuation bandwidth and attenuation strength. Subsequently, a design strategy is proposed, and used to tune the frequency spacing to get a wide attenuation region. A parametric study is conducted to reveal the effects of the frequency spacing and damping ratio on the vibration suppression performance of the graded metamaterial beam: with increasing frequency spacing, the attenuation region first becomes wider, then multiple discrete attenuation regions appear; and with increasing damping ratio, the transmittance response becomes flatter. A piezoelectric metamaterial beam is used to implement the proposed design strategy. Using a synthetic shunt circuit, the ‘stiffness’ of the local resonator can be tuned using a piezoelectric transducer. The FEM simulation results agree well with the developed theory for the graded metamaterial beam: with tuning of the capacitance spacing (2.4 nF), the attenuation bandwidth can be increased by about 172.8% as compared to the conventional one shunted with identical capacitances.
Advances in low power design open the possibility to harvest ambient energies to power directly the electronics or recharge a secondary battery. The key parameter of an energy harvesting (EH) device ...is its efficiency, which strongly depends on the conversion medium. To address this issue, metamaterials, artificial materials and structures with exotic properties, have been introduced for EH in recent years. They possess unique properties not easily achieved using naturally occurring materials, such as negative stiffness, mass, Poisson's ratio, and refractive index. The goal of this paper is to review the fundamentals, recent progresses and future directions in the field of metamaterials-based enhanced energy harvesting. An introduction on EH followed by the classification of potential metamaterials for EH is presented. A number of theoretical and experimental studies on metamaterials-based EH are outlined, including phononic crystals, acoustic metamaterials, and electromagnetic metamaterials. Finally, we give an outlook on future directions of metamaterials-based energy harvesting research including but not limited to active metamaterials-based EH, metamaterials-based thermal EH, and metamaterials-based multifunctional EH capabilities.
Over the past 5 years, digital coding and programmable metamaterials have been developed rapidly since their first exhibition in 2014. The iconic feature of the digital coding metamaterial is using ...digital codes like “0” and “1” to represent the distinct electromagnetic (EM) responses. This seemingly trivial progress has successfully reform the design theory from the effective medium to coding patterns, bridging the physical world and digital information world. More interestingly, beyond the simple coding on the parameters or patterns, the digital coding metamaterials are more intend to introduce the concept of direct interactions and operations of digital information within EM fields, to realize information processing, transmission or recognition. To accurately exhibit the informational specialties, we classify the coding metamaterials, digital metamaterials and programmable metamaterials, as well as other information-operating metamaterials, as
information metamaterials
. In this review article, we firstly introduce the digital coding concept, working mechanism, and related design methods. Then, three important theories including the scattering pattern calculation, convolution operation, and entropy of digital coding metamaterials, are discussed in details. Finally we introduce several system-level works based on the information metamaterials, such as the new-architecture wireless communication systems and reprogrammable imaging systems, to show the powerful manipulation capabilities of information metamaterials. As the next generation of information metamaterials, two proof-of-concept smart metamaterials and their advanced architectures are discussed. In the summary, the development track of information metamaterials and future trends are presented.
Attenuating low-frequency sound remains a challenge, despite many advances in this field. Recently-developed acoustic metamaterials are characterized by unusual wave manipulation abilities that make ...them ideal candidates for efficient subwavelength sound control. In particular, labyrinthine acoustic metamaterials exhibit extremely high wave reflectivity, conical dispersion, and multiple artificial resonant modes originating from the specifically-designed topological architectures. These features enable broadband sound attenuation, negative refraction, acoustic cloaking and other peculiar effects. However, hybrid and/or tunable metamaterial performance implying enhanced wave reflection and simultaneous presence of conical dispersion at desired frequencies has not been reported so far. In this paper, we propose a new type of labyrinthine acoustic metamaterials (LAMMs) with hybrid dispersion characteristics by exploiting spider web-structured configurations. The developed design approach consists in adding a square surrounding frame to sectorial circular-shaped labyrinthine channels described in previous publications (e.g. (11)). Despite its simplicity, this approach provides tunability in the metamaterial functionality, such as the activation/elimination of subwavelength band gaps and negative group-velocity modes by increasing/decreasing the edge cavity dimensions. Since these cavities can be treated as extensions of variable-width internal channels, it becomes possible to exploit geometrical features, such as channel width, to shift the band gap position and size to desired frequencies. Time transient simulations demonstrate the effectiveness of the proposed metastructures for wave manipulation in terms of transmission or reflection coefficients, amplitude attenuation and time delay at subwavelength frequencies. The obtained results can be important for practical applications of LAMMs such as lightweight acoustic barriers with enhanced broadband wave-reflecting performances.
Plasmonic meta-atoms and metasurfaces Meinzer, Nina; Barnes, William L; Hooper, Ian R
Nature photonics,
12/2014, Letnik:
8, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Despite the extraordinary degree of interest in optical metamaterials in recent years, the hoped-for devices and applications have, in large part, yet to emerge. It is becoming clear that the first ...generation of metamaterial-based devices will most probably arise from their two-dimensional equivalents -- metasurfaces. In this Review, we describe recent progress in the area of metasurfaces formed from plasmonic meta-atoms. In particular, we approach the subject from the perspective of the fundamental excitations supported by the meta-atoms and the interactions between them. We also identify some areas ripe for future research and indicate likely avenues for future device development.
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