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Bridging the terahertz gap requires synergism between the microwave and photonic communities. Advances in each of these two communities are often complementary but sometimes overlooked. One example is the manipulation of waves, known as anomalous diffraction via the use of metamaterials. This is achieved by controlling the surface impedance of each pixel at the interface of two different materials or alternately the phase and magnitude of the wave diffracted off the pixel. In this paper, a review of developments in wave manipulation from microwave to optical frequencies is presented, together with our new results in the terahertz regime. Generation of phase curves for pixel design requires a priori information on material properties at terahertz frequencies. Fabrication of terahertz devices entails micromachining in the clean room while their experimental validation demands both amplitude and phase information. Through judicial selection of practices in microwave and photonic communities, we can further the exploration of wave phenomena at terahertz frequencies.

A modification of effective medium theory for two-component nonmagnetic metal---dielectric metamaterials is developed for use in the microwave frequency range. The metamaterial is represented as an unbounded isotropic dielectric host material with periodically embedded nonmagnetic metallic inclusions of cylindrical or spherical shape. The effective electromagnetic response of the metamaterial is represented by the tensor of the effective relative permittivity and tensor of the effective relative permeability. The losses of the metamaterial are also evaluated in this study. A physical interpretation for the nature of the effective properties of such metamaterials is given. Analytical models of the proposed effective medium theory are benchmarked against numerical simulations using commercial electromagnetic software. Two compact microwave rectangular dual-band patch antennas on such metamaterial substrates are designed in this study.

‘Nonlinear invisibility cloak’ using metamaterial is presented in this paper. To comprehend the said, the notion of point source, cylindrical source, perfect metamaterials and reduced metamaterials are taken for cloaking application. Transformation optics to the metamaterial envisages an interesting variation of both clocking shape and cloaking area with respect to aspect ratio. Simulation results revealed that both cloaking area and cloaking configuration are changed nonlinearly in case of (point source, exact metamaterial), (point source, reduced metamaterial), (cylindrical source, exact metamaterial) and (cylindrical source, reduced metamaterial).

Extensive research in the electromagnetics area has been conducted recently with the goal of developing novel artificial metamaterials-or left-handed (LH) materials-at microwave frequencies. The idea of negative magnetic permeability and negative electric permittivity as electromagnetic properties for LH materials was initially theorized by Veselago in 1968 [1]. LH materials are not found in nature, so engineers must modify a structure's geometry to achieve LH behavior.

Absorbers play an important role in protecting sensitive electronic devices from electromagnetic interference by absorbing the energy of incoming waves and reducing unnecessary reflection or transmission. In this paper we introduce new types of absorbers based on periodic structures, or the so-called metamaterials, which give us additional degrees of freedom to design the absorbing performance of absorbers with reduced thicknesses. Specifically, we demonstrate two types of metamaterial absorbers: one allowing us to customize absorption and other scattering parameters at selected frequencies; another absorbing only high-power microwaves and transmitting small signals even at the same frequency to maintain wireless communications. These metamaterial absorbers are expected to facilitate solving modern, complex EM interference issues where different-interdependent requirements exist.

Applications of metamaterials have been limited by parasitic resistive losses. We present the design and measurement of split ring resonators with embedded active field effect transistor circuits comprising a magnetic metamaterial. We show that the imaginary part of the effective permeability changes sign within the bandwidth of the negative differential resistance region, creating a stable gain medium. We present experimental reflection and transmission measurements showing a sign change in the permeability loss term and two applications of such a metamaterial. use as a mu-negative near field parasitic element for small magnetic antennas and as an amplifying material in free space. We show the active metamaterial can provide property enhancement compared with related passive structures in both applications, providing a path to overcoming parasitic loss in previously demonstrated metamaterial structures.

Three-dimensional structure terahertz metamaterial absorbers with the properties of ultrabroadband and polarization-insensitive absorption were proposed. Different from the recent designs of the multilayer horizontal configurations, our design consists of the uniaxial anisotropic gold nanowire arrays that are filled in the frustum pyramid dielectric medium. The principle for the ultrabroadband absorption originates from the overlapping of the different but very closely positioned electromagnetic resonances. Each resonance frequency follows the equation of the odd multiple of the quarter wavelengths, which can be flexibly controlled by varying the height of the corresponding gold nanowires. In addition to the great prospect for the potential applications in terahertz, our design could also be easily extended to the other frequency regimes for a host of applications such as electromagnetic stealth, infrared detection, imaging, and solar cell.

In this work, we investigate wave propagation through a zero index meta-material (ZIM) waveguide embedded with triangular dielectric defects. We provide a theoretical guidance on how to achieve total reflection and total transmission (i.e., cloaking) by adjusting the defect sizes and/or permittivities of the defects. Our work provides a systematical way in manipulating wave propagation through ZIM in addition to the widely studied dielectric defects with cylindrical and rectangular geometries.

Recently, metamaterials with near-zero refractive index have attracted much attention. Light inside these materials experiences no spatial phase change and extremely large phase velocity, makes these peculiar systems applicable for realizing directional emission, tunneling waveguides, large-area single-mode devices and electromagnetic cloaks. In addition, epsilon-near-zero (ENZ) metamaterials can also enhance light transmission through a subwavelength aperture. Impedance-matched all-dielectric zero-index metamaterials which exhibit Dirac cone dispersions at center of the Brillouin zone, have been experimentally demonstrated at microwave regime and optical frequencies for transverse-magnetic (TM) polarization of light. More recently, it has been also proved that these systems can be realized in a miniaturized in-plane geometry useful for integrated photonic applications, i.e. these metamaterials can be integrated with other optical elements, including waveguides, resonators and interferometers. In this work, using a zero-index metamaterial at the inner and outer sides of a subwavelength aperture, we numerically and experimental study light transmission through and its extraction from the aperture. The metamaterial consists of a combination of two double-layer arrays of scatterers with dissimilar subwavelength dimensions. The metamaterial exhibits zero-index optical response in microwave region. Our numerical investigation shows that the presence of the metamaterial at the inner side of the aperture leads to a considerable increase in the transmission of light through the subwavelength aperture. This enhancement is related to the amplification of the amplitude of the electromagnetic field inside the metamaterial which drastically increases the coupling between free space and the slit. By obtaining the electric field profile of the light passing through the considered NZI/aperture/NZI system at this frequency we found out that in addition to the enhanced transmission there is an excellent beaming of the extracted light from the structure. We have theoretically and experimentally shown that using a zero-index metamaterial at the inner and outer sides of a metallic subwavelength slit can considerably enhance the transmission of light through the aperture and beam its extraction, respectively. This work has been supported by TUBITAK under Project No 114E505. The author H.C. also acknowledges partial support from the Turkish Academy of Sciences.

Transformation optics makes use of coordinate transformations to explore the possibilities offered by artificially structured metamaterials for the manipulation of a wide variety of electromagnetic phenomena. Since a decade, transformation optics has consistently extended its scope. Initially, coordinate transformations were only applied to the transformation of light in the simplest of optical setups, i.e., empty space [1,2]. In particular, straight light trajectories were being transformed into curved ones, e.g., avoiding a specific region in space (invisibility devices), bending over a specific angle (benders and splitters), and focussing to a particular point (lenses). Today, research efforts go beyond the transformation of empty space, allowing metamaterials to further enhance our control on electromagnetic phenomena other than light propagation. In this contribution, I will review our work on transformation optics to manipulate guided modes along and optical forces between metamaterial waveguides [3,4], the emission of Cerenkov radiation due to fast charged particles [5,6], and the Goos-Hanchen shift at metamaterial surfaces [7].

Main relations of microwave RLC-circuit effective medium theory of two-component metamaterials are presented in this paper. The metamaterials are infinite isotropic dielectric host media with periodically embedded non-magnetic metallic wires of circular cross section or non-magnetic metallic spheres. The microwave approximations for the effective linear lumped parameters of equivalent RLC-circuits are obtained for the unit cell of each metamaterial. The validation of the effective linear lumped parameters is made using the test numerical simulation.

In this paper, metamaterials are regarded as a kind of specific medium. The application of three-dimensional electromagnetic field finite element mesh generation methods makes a finite element analysis and calculates the integral to metamaterials and its surrounding spatial structures so as to solve the spatial distribution of meta-materials and its surrounding electromagnetic parameter B and H under a certain frequency. In this way, the spatial distribution of the magnetic pole field in the metamaterials is obtained. Then, the process of making an integral treatment of it would give rise to the equivalent magnetic polarizability of the metamaterials.

We theoretically studied how to directly engineer the constitutive parameters of metamaterials for perfect absorbers of electromagnetic waves. As an example, we numerically investigated the necessary refractive index n and extinction coefficient k and the relative permittivity ε and permeability μ of a metamaterial anti-reflection layer, which could cancel the reflection from a hydrogenated amorphous silicon (α-Si:H) thin film on a metal substrate, within the visible wavelength range from 300 to 800 nm. We found that the metamaterial anti-reflection layer should have a negative refractive index (n 0) for long-wavelength visible light. The relative permittivity ε and permeability μ could be fitted by the Lorentz model, which exhibited electric and magnetic resonances, respectively.

Metamaterials have aroused tremendous interests in recent years owing to their peculiar electromagnetic (EM) properties and fascinating potential applications, e.g., invisibility cloak, perfect lens, etc.

An electromagnetic cloaking device made with composite materials and operating in the range of near-infrared light is presented. The invisibility cloak is designed with transformation optics and consists of 15 concentric rings of different anisotropic two-phase metal-dielectric composites. The anisotropic material parameters of the nanocomposites are expressed with the Maxwell-Garnett mixing rule. The finite element simulation of the concealment produced by the multilayer nanocomposite is discussed. The geometry of the inclusions and the material parameters of the composites are determined with differential evolution-based optimization.

In this letter, we present a nonlinear metamaterial capable of transitioning between a broadband reflective and broadband nonreflective state depending on the incident power level. Below the activation voltage, broadband reflectivity is created by forbidding propagation through the metamaterial as a result of the effective permittivity and permeability having different signs. Above the activation voltage, reflection is suppressed by matching the effective permittivity and permeability. Full-wave simulations are performed to analyze the electromagnetic characteristics of the structure, with experimental results presented at S-band frequencies in a WR-284 waveguide. These measurements demonstrate a 10 dB reduction in reflected amplitude over an 18% bandwidth, a 3-dB reduction over a greater than 30% bandwidth, and a maximum difference in reflection of nearly 42 dB.

The approximate cloaking is investigated for time-harmonic Maxwell's equations via the approach of transformation optics. The problem is reduced to certain boundary effect estimates due to an inhomogeneous electromagnetic inclusion with an asymptotically small support but an arbitrary content enclosed by a thin high-conducting layer. Sharp estimates are established in terms of the asymptotic parameter, which are independent of the material tensors of the small electromagnetic inclusion. The result implies that the “blow-up-a-small-region” construction via the transformation optics approach yields a near-cloak for the electromagnetic waves. A novelty lies in the fact that the geometry of the cloaking construction of this work can be very general. Moreover, by incorporating the conducting layer developed in the present paper right between the cloaked region and the cloaking region, arbitrary electromagnetic contents can be nearly cloaked. Our mathematical technique extends the general one developed in [H. Y...

Remarkable progress has been made over the past decade in controlling light propagation and absorption in compact devices using nanophotonic structures and metamaterials. From sensing and modulation, to on-chip communication and light trapping for solar cells, new device applications and opportunities motivate the need for a rigorous understanding of the modal properties of metamaterials over a broad range of frequencies. In this review, we provide an overview of a metamaterial band theory we have developed that rigorously models the behavior of metamaterials made of dispersive materials such as metals. The theory extends traditional photonic band theory for periodic dielectric structures by coupling the mechanical motion of electrons in the metal directly to Maxwell’s equations. The solution for the band structures of metamaterials is then reduced to a standard matrix eigenvalue problem that nevertheless fully takes into account the dispersive properties of the constituent materials. As an application of the metamaterial band theory, we show that one can develop a perturbation formalism based on this theory to physically explain and predict the effect of dielectric refractive index modulation or metallic plasma frequency variation in metamaterials. Furthermore, the metamaterial band theory also provides an intuitive physical picture of the source of modal material loss, as well as a rigorous upper bound on the modal material loss rate of any plasmonic, metamaterial structure. This in turn places fundamental limits on the broadband operation of such devices for applications such as photodetection and absorption.

Microwave metamaterials show promise in numerous low-power applications, ranging from strip lines to antennas. In general, metamaterials allow microwave designers to obtain electromagnetic characteristics not typically available in nature, leading to new behavior as well as reductions in the size of typical devices. High-power microwave (HPM) sources were efficient in the conventional microwave source community. We consider a specific use of metamaterials as a method to reduce the size of waveguide used for power transmission, particularly, a configuration in which an array of split-ring resonators (SRRs), forming a “mu-negative” structure, allows transmission of power in a waveguide well below the cutoff frequency. This configuration would not be used in an actual HPM device, but explores the methods and considerations that might be required for developing a metamaterial structure for either making HPM sources more compact or developing new types of interaction at these high powers. For any HPM application, a microwave structure must be able to sustain high electric and magnetic fields, as well as high peak and possibly average power. The challenge for metamaterials consists of devising the subwavelength structures (a defining characteristic of metamaterials) that can sustain such fields. In particular, one must understand the sensitivity of any metamaterial system to changes in the individual elements, which in high power pertains mainly to the loss of an individual resonator element. As such a sample system, we explore the physical operating characteristics of the waveguide system loaded with an array of SRRs, particularly the role of defects on its properties. Such defects would form an important feature in any high-power application in which subwavelength structures can be damaged by high field stresses.

We achieve strong local-field enhancement within a novel inhomogeneous metamaterial whose graded refractive index is realized using Dirac-cone metamaterials. This transition metamaterial provides a powerful tool for sensing, nonlinear optics, and quantum optics.

In this paper,the electromagnetic responses and potential applications of THz metamaterials are reviewed through the focus on fabrication,unit structure design,and material selection,respectively.It describes different kinds of fabrication technologies for obtaining metamaterials with special electromagnetic responses such as magnetic resonance and reconfigurable tunability,which is helpful for further understanding of electromagnetic resonances in metamaterials.The paper analyzes the electromagnetic response characteristics in detail and points out that the unit structure design can be used to obtain desired electromagnetic characteristics,such as anisotropy,bianisotropy,polarization modulation,multiband response,broadband response,asymmetric transmission,optical activity,and perfect absorption,etc.The dependence of electromagnetic responses upon surrounding dielectrics can be used not only to control resonant frequency by a proper substrate selection,but also for sensing applications.Furthermore,the introduction of functional materials with controllable dielectric properties by external optical field,electrical field,magnetic field and temperature has the potential to achieve tunable metamaterials,which is highly desirable for THz functional devices.Finally,the opportunities and challenges for further developments of THz metamaterials are briefly introduced.

A self-assembled metamaterial exhibiting a positive near-zero index of refraction at visible wavelengths is demonstrated. The metamaterial consists of thiolene-functionalized gold nanospheres self-assembled into macroscopic, crosslinked, monolayers. By measuring the real and imaginary parts of the phase shift of light transmitted through the self-assembled films the effective index of refraction is determined as a function of wavelength. These findings may pave a way to simply and efficiently self-assemble and optically characterize multifunctional, multilayer nanoparticle–ligand metamaterials.

A metamaterial is a composite material that has attracted the attention of researchers since the late 1990s-early 2000s. This material contains an artificial periodic structure, which modifies its permittivity and permeability and, thereby, makes it possible to control the dispersion, refraction, and reflection of electromagnetic waves in the metamaterial. Analytical and experimental studies of the properties of metamaterials, as well as their applications, cover a wide frequency range from radio waves to the visible range. In recent years, considerable progress has been made toward the application of these materials in the microwave range (1–100 GHz). Works on development and application of metamaterials in the microwave range published over the last 8–10 years are reviewed. Artificial transmission lines as 1D metamaterials are discussed. Resonators, filters, and phase shifters based on the “metamaterial philosophy” are considered. Special attention is given to the application of metamaterials in the antenna technology.

Advances in metamaterials and metasurfaces have enabled unprecedented control of light-matter interactions. Metamaterial constituents support high-frequency electric and magnetic dipoles, which can be used as building blocks for new materials capable of negative refraction, electromagnetic cloaking, strong visible-frequency circular dichroism, and enhanced magnetic or chiral transitions in ions and molecules. However, most metamaterials to date have been limited to solid-state, static, narrow-band, and/or small-area structures. Here, we introduce the design, fabrication, and three-dimensional nano-optical characterization of large-area, dynamically-tunable metamaterials and gram-scale metafluids. First, we use transformation optics to design a broadband metamaterial constituent - a metallo-dielectric nanocrescent - characterized by degenerate electric and magnetic dipoles. A periodic array of nanocrescents exhibits large positive and negative refractive indices at optical frequencies, confirmed through simulations of plane wave refraction through a metamaterial prism. Simulations also reveal that the metamaterial optical properties are largely insensitive to the wavelength, orientation and polarization of incident light. Then, we introduce a new tomographic technique, cathodoluminescence (CL) spectroscopic tomography, to probe light-matter interactions in individual nanocrescents with nanometer-scale resolution. Two-dimensional CL maps of the three-dimensional nanostructure are obtained at various orientations, while a filtered back projection is used to reconstruct the CL intensity at each wavelength. The resulting tomograms allow us to locate regions of efficient cathodoluminescence in three dimensions across visible and near-infrared wavelengths, with contributions from material luminescence and radiative decay of electromagnetic eigenmodes. Finally, we demonstrate the fabrication of dynamically tunable large-area metamaterials and gram-scale metafluids, using a combination of colloidal synthesis, protein-directed assembly, self-assembly, etching, and stamping. The electric and magnetic response of the bulk metamaterial and metafluid are directly probed with optical scattering and spectroscopy. Using chemical swelling, these metamaterials exhibit reversible, unity-order refractive index changes that may provide a foundation for new adaptive optical materials in sensing, solar, and display applications.

Transformation optics provides a geometry-based tool to create new components taking advantage of artificial metamaterials with optical properties that are not available in nature. Unfortunately, although guided electromagnetic waves are crucial for optical circuitry, transformation optics is not yet compatible with two-dimensional slab waveguides. Indeed, after determining the propagation of confined waves along the waveguide with a two-dimensional coordinate transformation, the conventional application of transformation optics results in metamaterials whose properties are insensitive to the coordinate perpendicular to the waveguide, leading to bulky, and therefore impractical, designs. In this contribution, we formulate an alternative framework that leads to feasible coordinate-based designs of two-dimensional waveguides. To this end, we characterize a guided transverse-magnetic light mode by relevant electromagnetic equations: a Helmholtz equation to account for wave propagation and a dispersion relation to impose a continuous light profile at the interface. By considering how two-dimensional conformal transformations transform these equations, we are able to materialize the coordinate-designed flows with a nonmagnetic metamaterial core of varying thickness, obtaining a two-dimensional device. We numerically demonstrate the effectiveness and versatility of our equivalence relations with three crucial functionalities, a beam bender, a beam splitter and a conformal lens, on a qualitative and quantitative level, by respectively comparing the electromagnetic fields inside and the transmission of our two-dimensional metamaterial devices to that of their three-dimensional counterparts at telecom wavelengths. As a result, we envision that one coordinate-based multifunctional waveguide component may seamlessly split and bend light beams on the landscape of an optical chip. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

While typically designed to manipulate classical light, metamaterials have many potential applications for quantum optics as well. We argue why a quantum optical effective-medium theory is needed. We present such a theory for layered metamaterials that is valid for light propagation in all spatial directions, thereby generalizing earlier work for one-dimensional propagation. In contrast to classical effective-medium theory there is an additional effective parameter that describes quantum noise. Our results for metamaterials are based on a rather general Lagrangian theory for the quantum electrodynamics of media with both loss and gain. In the second part of this paper, we present a new application of transformation optics whereby local spontaneous-emission rates of quantum emitters can be designed. This follows from an analysis how electromagnetic Green functions trans- form under coordinate transformations. Spontaneous-emission rates can be either enhanced or suppressed using invisibility cloaks or gradient index lenses. Furthermore, the anisotropic material profile of the cloak enables the directional control of spontaneous emission. MOE (Min. of Education, S’pore) Published version

A real-space gauge field provides an alternative way in bending light by shifting the local dispersion surfaces instead of changing their shapes or sizes in conventional gradient index media. Here, we show that such gauge field can be realized by anisotropic metamaterials. A metamaterial structure with balanced electric and magnetic responses is designed to materialize such gauge field. By combining with transformation optics, it allows us to design spin-dependent optical devices. A unidirectional retroreflector is demonstrated as an example.

In this talk, we present two experimental works on transformation optics and metamaterials in microwave frequency and electrostatics. The first is an experimental verification to an all-dielectric semi-spherical lens in the microwave regime, which exhibits extraordinary functions in shaping three-dimensional (3D) wave-propagation paths. On one hand, it was heuristically found that when radiation sources are placed in the central region, the lens behaves as a magnifying device, which resolves the sources in subwavelength scale. On the other hand, when impinging on the same semi-spherical lens from outside, the electromagnetic waves will be guided spirally inwards and absorbed efficiently by a normal absorber on the bottom surface. The 3D lens is composed of isotropic non-resonant metamaterials, which is fabricated by judiciously drilling inhomogeneous air holes in multi-layered dielectric plates. In electrostatics, the transformation optics will degenerate to transformation electrostatics. We present the concept of multi-functional transformation-dc devices, in which the functions of dc metamaterials can be remotely altered by illuminating visible light. We design, fabricate and test the anisotropic and inhomogeneous dc metamaterials using resistor network with light-sensitive semiconductor resistors embedded. When the illuminated light turns off, the dc device acts as an invisibility cloak; when we adjust the light power, the dc device exhibits various electrostatic illusions correspondingly. If the light-induced dc illusion effect is activated, the electrostatic behavior of the original object is perceived as multiple equivalent objects with different predesigned geometries. The experimental results of the functional device are in good agreement with the numerical simulations, which makes it possible to control the sophisticated passive transformation-dc devices using external light illuminations.

Conventional metamaterials are characterized by effective permittivity and permeability with continuous values. In analogy to the digital circuit that has only two distinct states ‘on’ and ‘off’, we proposed the concept of coding metamaterials, which is realized by distributing coding particles ‘0’ and ‘1’ with opposite reflection phases on a metasurface with a certain coding sequence. In this talk, we will introduce the concept of coding metamaterial, broadband diffusion of terahertz waves realized by the coding metamaterials, polarization-controlled anisotropic coding metamaterials, generation of single-beam THz radiations with arbitrary direction, and the information entropy of coding metasurfaces.

This paper presents a double split-ring resonators array fabricated on parylene-C substrates. We designed four structures with different angles of the outer and inner split-ring resonators to achieve tunability of the metamaterial and investigated the effect of polarization direction of terahertz waves on the transmission of metamaterials. Finite-difference time-domain (FDTD) numerical simulations were conducted to calculate the transmission spectra and the electromagnetic field as well as surface current distributions. In general, our simulation results agree with the measurements to some extent.

Electromagnetic metamaterials (MMs) consisting of highly conducting sub-wavelength metallic resonators enable many unusual electromagnetic properties at user defined frequencies which are not permissible with the naturally occurring materials [1, 2]. Generally the electromagnetic properties of metamaterials are controlled by the design variation of the MM unit cell, often termed as meta-molecule, consisting of single or multiple metallic split ring resonators (SRRs). These metallic resonators are quite often termed as meta-atoms too. The near field electromagnetic coupling between these meta-atoms exhibits an important role in modulating the fundamental resonances of the metamaterials [3–5].

Metamaterials are artificial materials formed by highly subwavelength inclusions embedded in a host medium, which yield homogenized permittivity and permeability values. They offer electromagnetic unusual responses not generally available in nature. The aim of this paper is to provide a historical overview of electromagnetic (EM) metamaterials throughout last century, with the main focus on microwave and antennas applications.

We review the connection between transmission-line metamaterials (TL-MTMs) and the transmission-line matrix (TLM) method for solving Maxwell's equations numerically. We show historically how the two disciplines evolved and how they are intimately related to each other We use the TLM method to reveal and explain the physics of the negative index property characterizing certain classes of transmission-line metamaterials as well as to inspire new research avenues in TL-MTMs.

In this paper, we experimentally validate the effects of different structures of metamaterial on efficiency enhancement in a four-coil magnetic resonant wireless power transfer system operating at 6.78MHz. First, we propose a concise design of magnetic metamaterials. A 6×6 planar array metamaterial slab is simulated to investigate its effect on power transmission between transmitter and receiver. The proposed metamaterials are fabricated for their application in the wireless power transfer system. Transmission and reflection coefficients of the system with 1-dimentional (including 1-slab and 2-slab), 2-dimentional, and 3-dimentional metamaterials at different positions are measured to investigate their influence on power transmission and to optimize the position of metamaterials in each case. Finally, the platform with metamaterials is utilized to light a 15W bulb to explicitly demonstrate the efficiency enhancement.

In this paper, an efficient magnetic resonance-based wireless power transfer (MRWPT) system with metamaterials is proposed. The negative permeability (MNG) metamaterials for this system with low-megahertz frequency is designed, which can be adjusted to work well at a variable receiving angle ranging from 0° to 45° along z-direction. The S-parameters, resonant frequency and permeability of metamaterials are computed for analysis. The transmission efficiency of the multiple-receiver MRWPT system in free space is compared to that in the presence of metamaterials placed in front of transmission and receive coils. The measured results show that the performance of the proposed metamaterials is perfect in improving the efficiency with incident electromagnetic waves from various directions.

The advent of metamaterials with tailorable frequency dispersion ensured the emergence of transformation optics with proposed applications that include cloaking devices, superconcentrators, superabsorbers, beam shapers and benders, field and polarization rotators, etc. A crucial property of interest for transformation optics is the possibility to custom design the spatial dependence of optical properties, i.e. to attain a gradient of effective refractive index. The cylindrical geometry has been one of the prototypal proposed forms and actually the first theoretical and experimental cloaking devices had radial symmetry. In this contribution we present an exact analytical approach to the solution of Helmholtz’ equations applied to radial propagation of electromagnetic waves through a cylinder containing negative and positive refractive index parts. A hyperbolic tangent gradient of refractive index is assumed. Our approach is inspired by the correspondence between transformation optics and quantum mechanics. A remarkably simple exact analytical solution is derived that takes into account realistic losses in negative-positive refractive index material composites.

Almost a decade ago, transformation optics established a geometrical perspective to describe the interaction of light with structured matter, enhancing our understanding and control of light. However, despite their huge technological relevance in applications such as optical circuitry, optical detection, and actuation, guided electromagnetic waves along dielectric waveguides have not yet benefited from the flexibility and conceptual simplicity of transformation optics. Indeed, transformation optics inherently imposes metamaterials not only inside the waveguide's core but also in the surrounding substrate and cladding. Here we restore the two-dimensional nature of guided electromagnetic waves by introducing a thickness variation on an anisotropic dielectric core according to alternative two-dimensional equivalence relations. Our waveguides require metamaterials only inside the core with the additional advantage that the metamaterials need not be magnetic and, hence, our purely dielectric waveguides are low loss. We verify the versatility of our theory with full wave simulations of three crucial functionalities: beam bending, beam splitting, and lensing. Our method opens up the toolbox of transformation optics to a plethora of waveguide-based devices.

Metamaterials with tunable negative permeability are proposed and investigated theoretically in this paper. First, the model of the dielectric bilayer sphere embedded in the dielectric substrate is put forward. Second, expressions of the electromagnetic fields in the model are derived based on the Mie scattering theory, and the general formula for the effective permeability of the model is deduced via the Maxwell-Garnett theory, which is further verified through the simulation results. Finally, the tunable bandwidth of the negative permeability of the metamaterials changing with the geometrical parameters is investigated based on the full-wave simulations, and the relative mechanisms are also discussed. It is believed that the results would be helpful for the practical applications of the metamaterials, and the metamaterials with tunable negative permeability proposed in the paper would facilitate the constructions of the left-handed materials in some degree.

The properties and applications of different types of ceramic all-dielectric metamaterials are presented. Metamaterials composed of arrays of identical ceramic resonators are shown to provide for negative refraction, enhanced transmission, and backward wave propagation. It is also demonstrated that arrays of dielectric elements can be used as non-resonant metamaterials to form a gradient index medium. Employment of such media in antenna substrates is shown perspective for antenna miniaturization without deteriorating antenna parameters. The development of a microwave transmission cloak composed of identical low-loss ceramic resonators to conceal object with the dimensions far exceeding the wavelength of incident radiation is also described.

Based on the quantization scheme of the radiation fields in the dispersive and absorptive magnetic media, the normally ordered correlation functions of the outgoing field through a metamaterial plate are obtained. Then the relative photon-number densities of the transmitted field, the reflected field and the absorbed field are gotten through the correlation functions. Furthermore, the contributions of the relative permittivity and permeability of the metamaterials to the transmission are analyzed. Our results show that the permittivity and permeability reinforce the transmission for frequencies that are big compared with the magnetic resonance frequency.

Highly efficient and versatile computational electromagnetic analysis of 3-D transformation-based metamaterial cloaking structures based on a hybridization of a higher order finite element method for discretization of the cloaking region and a higher order method of moments for numerical termination of the computational domain is proposed and demonstrated. The technique allows for an effective modeling of the continuously inhomogeneous anisotropic cloaking region, for cloaks based on both linear and nonlinear coordinate transformations, using a very small number of large curved finite elements with continuous spatial variations of permittivity and permeability tensors and high-order p-refined field approximations throughout their volumes, with a very small total number of unknowns. In analysis, there is no need for a discretization of the permittivity and permeability profiles of the cloak, namely for piecewise homogeneous (layered) approximate models, with material tensors replaced by appropriate piecewise constant approximations. Numerical results show a very significant reduction (three to five orders of magnitude for the simplest possible 6-element model and five to seven orders of magnitude for an h-refined 24-element model) in the scattering cross section of a perfectly conducting sphere with a metamaterial cloak, in a broad range of wavelengths. Given the introduced explicit approximations in modeling of the spherical geometry and continuous material tensor profiles (both by fourth-order Lagrange interpolating functions), and inherent numerical approximations involved in the finite element and moment method techniques and codes, the cloaking effects are shown to be predicted rather accurately by the full-wave numerical analysis method.

Stealth technology in terms of absorption of electromagnetic waves is a most valuable research area for military purposes. Development of radar absorbing materials (RAM) had been actively researched for a quite long time. In the RAM design, weight, thickness, absorptivity, environmental resistance and mechanical strength are the key factors and therefore development of RAM with low density and high strength is a challenging task. As an alternative, research interest has shifted towards radar absorbing structures (RAS) and metamaterial is one of the lucrative options for the development of RAS. Metamaterials are a new class of ordered composites that exhibit exceptional electromagnetic properties not readily observed in nature. Built from microstructure that is small compared to wavelength of operation, metamaterials can be designed with effective permittivity and permeability values that can be large or small or even negative at any selected frequency. In this review paper, we first place the stealth technology in brief and then concept of metamaterials in context of conventional materials. We then discuss reflection theory of metamaterials from stealth point of view. Next section deals with recent progress towards its application as electromagnetic absorbers and future prospects especially in higher frequency region. Defence Science Journal, 2012, 62(4), pp.261-268 , DOI:http://dx.doi.org/10.14429/dsj.62.1514

In this article, we present a new theory to explain the phenomenon of negative refraction in bulk metamaterials. Unlike earlier theories, it does not rely on the existence of a single mode of propagation in materials with negative constitutive parameters. It is based on the interaction and phase reversal effects caused by the existence of two simultaneous electromagnetic (EM) modes in uniform inhomogeneous metamaterial structures. The theory is general in the sense that it may be applied with equal validity to quasilumped circuit-based microwave metamaterials and to optical negative refraction in bulk nanowire metamaterials. Validity of the theory is demonstrated with EM simulations of microwave and optical metamaterials.

The growing and rapid interest in new artificial metamaterials, whose properties differ from the normal materials has motivated further investigations. The metamaterials have simultaneously negative permittivity and permeability. In this work, we have demonstrated theoretically the existence and behavior of the TE guided waves in a ferromagnetic/metamaterial/antiferromagnetic waveguide structure. The dispersion characteristics are performed for different kinds of metamaterials. The existence and the type of the solutions to the guided waves with respect to different physical parameters are also investigated and discussed. It has been shown that the metamaterials can lead to different, new unusual properties.

The distribution of the electromagnetic field in a waveguide or slit is generally dependent on its shape and size. In this paper, we develop a general method to arbitrarily control the electromagnetic field through metamaterials, of which permittivity and/or permeability can be designed to continuously change from negative to positive values. With this method, the field distribution in a two-dimensional arbitrarily shaped waveguide or slit is totally dependent on the electromagnetic properties of metamaterials filled inside, but not on its shape or size. Permittivity and permeability of the metamaterials are derived, and transmission properties in the waveguide and slit are validated by numerical simulation. Results show that the field distribution inside the waveguide and slit can be easily controlled by the metamaterials. It provides a feasible way to control the electromagnetic field distribution.

The major issue regarding magnetic response in nature—“negative values for the permeability μ of material parameters, especially in terahertz or optical region” makes the electromagnetic properties of natural materials asymmetric. Recently, research in metamaterials has grown in significance because these artificial materials can demonstrate special and, indeed, extraordinary electromagnetic phenomena such as the inverse of Snell’s law and novel applications. A critical topic in metamaterials is the artificial negative magnetic response, which can be designed in the higher frequency regime (from microwave to optical range). Artificial magnetism illustrates new physics and new applications, which have been demonstrated over the past few years. In this review, we present recent developments in research on artificial magnetic metamaterials including split-ring resonator structures, sandwich structures, and high permittivity-based dielectric composites. Engineering applications such as invisibility cloaking, negative refractive index medium, and slowing light fall into this category. We also discuss the possibility that metamaterials can be suitable for realizing new and exotic electromagnetic properties.

This paper proposes the study and implementation of metamaterials in electromagnetic non-destructive examination; these materials can serve as electromagnetic flux concentrators in the radio frequency range. Thus, the use of new types of metamaterials, namely conical Swiss roll, is proposed. Here, we present a method of extracting the necessary parameters (effective magnetic permeability and the frequency) from the data obtained by measuring network parameters. Due to the fact that conical Swiss rolls can serve as radio frequency flux concentrators, they can be used in the fabrication of electromagnetic lenses, being designed on the basis of Fourier optic principles. As a direct application, carbon fibre reinforced plastic (CFRP) plates with and without delaminations, created by impacts with low energy, were examined by means of electromagnetic transducers with a metamaterial lens. The characteristics of a carbon fibre woven structure become visible and the delaminations are clearly emphasised.