Showing papers on "Transformation optics published in 2009"
TL;DR: An experimental realization of a cloak design that conceals a perturbation on a flat conducting plane, under which an object can be hidden, and results indicate that this type of cloak should scale well toward optical wavelengths.
Abstract: The possibility of cloaking an object from detection by electromagnetic waves has recently become a topic of considerable interest. The design of a cloak uses transformation optics, in which a conformal coordinate transformation is applied to Maxwell's equations to obtain a spatially distributed set of constitutive parameters that define the cloak. Here, we present an experimental realization of a cloak design that conceals a perturbation on a flat conducting plane, under which an object can be hidden. To match the complex spatial distribution of the required constitutive parameters, we constructed a metamaterial consisting of thousands of elements, the geometry of each element determined by an automated design process. The ground-plane cloak can be realized with the use of nonresonant metamaterial elements, resulting in a structure having a broad operational bandwidth (covering the range of 13 to 16 gigahertz in our experiment) and exhibiting extremely low loss. Our experimental results indicate that this type of cloak should scale well toward optical wavelengths.
1,405 citations
TL;DR: The optical 'carpet' cloak is designed using quasi-conformal mapping to conceal an object that is placed under a curved reflecting surface by imitating the reflection of a flat surface and enables broadband and low-loss invisibility at a wavelength range of 1,400-1,800 nm.
Abstract: Invisibility devices have captured the human imagination for many years. Recent theories have proposed schemes for cloaking devices using transformation optics and conformal mapping. Metamaterials, with spatially tailored properties, have provided the necessary medium by enabling precise control over the flow of electromagnetic waves. Using metamaterials, the first microwave cloaking has been achieved but the realization of cloaking at optical frequencies, a key step towards achieving actual invisibility, has remained elusive. Here, we report the first experimental demonstration of optical cloaking. The optical 'carpet' cloak is designed using quasi-conformal mapping to conceal an object that is placed under a curved reflecting surface by imitating the reflection of a flat surface. The cloak consists only of isotropic dielectric materials, which enables broadband and low-loss invisibility at a wavelength range of 1,400-1,800 nm.
1,318 citations
TL;DR: In this article, a dielectric optical cloak is designed using quasi-conformal mapping to conceal an object that is placed under a curved reflecting surface which imitates the reflection of a flat surface.
Abstract: Invisibility or cloaking has captured human's imagination for many years. With the recent advancement of metamaterials, several theoretical proposals show cloaking of objects is possible, however, so far there is a lack of an experimental demonstration at optical frequencies. Here, we report the first experimental realization of a dielectric optical cloak. The cloak is designed using quasi-conformal mapping to conceal an object that is placed under a curved reflecting surface which imitates the reflection of a flat surface. Our cloak consists only of isotropic dielectric materials which enables broadband and low-loss invisibility at a wavelength range of 1400-1800 nm.
955 citations
TL;DR: In this paper, the authors review the recent progress of Mie resonance-based metamaterials by providing a description of the underlying mechanisms to realize negative permeability, negative permittivity and double negative media.
752 citations
Book•
23 Nov 2009
TL;DR: In this paper, the authors provide an overview of optical cloaking with metamaterials and their applications in the field of transformation optics, including super resolution with meta-lenses, near-field superlens, and electric cloaking.
Abstract: Preface Chapter 1. Introduction What are metamaterials? Macroscopic effective parameters References Chapter 2. Optical Properties of Metal-Dielectric Composites Optical materials and electronic structures Optical properties of dielectric materials Optical properties of metals Metal-dielectric composites and mixing rules References Chapter 3. Experimental Techniques and Data Treatment Fabrication of two-dimensional optical metamaterials Approaching the third dimension Characterization of spectral properties Extraction of homogenized optical parameters References Chapter 4. Electric Metamaterials A brief overview of artificial dielectrics Optical properties of stratified metal-dielectric composites Periodic array of metallic wires Semicontinuous metal films References Chapter 5. Magnetic Metamaterials Negligible optical magnetism in nature Split-ring resonators Optical magnetic elements Magnetism in the visible spectrum Analytical model of magnetic nanostrips High-permittivity route to artificial magnetism References Chapter 6. Negative-Index Metamaterials A brief historical review Reversed phenomena in negative-index media Negative refraction in microwave frequencies The debut of optical negative-index materials General recipe for construction Alternative approaches References Chapter 7. Nonlinear Optics with Metamaterials Recent advances of nonlinear effects in metamaterials Second-harmonic generation and the Manley-Rowe relations in negative-index materials Optical parametric amplifications in negative-index materials References Chapter 8. Super Resolution with Meta-Lenses Perfect lens with subwavelength resolution Near-field superlens Tunable superlens using random composites Potential applications of the composite lens Far-field imaging with super-resolution References Chapter 9. Transformation Optics and Electromagnetic Cloak of Invisibility Invisibility and transformation optics: an overview Cloaking by coordinate transformation Towards experimental demonstrations Non-magnetic optical cloak Cloaking with high-order transformations Designs for high-order optical cloaking Alternative approaches for optical cloaking Concluding remarks on transformation optics References Index
705 citations
TL;DR: It is demonstrated theoretically that electromagnetically induced transparency can be achieved in metamaterials, in which electromagnetic radiation is interacting resonantly with mesoscopic oscillators rather than with atoms, and these results are confirmed by accurate simulations of the electromagnetic field propagation in the meetamaterial.
Abstract: We demonstrate theoretically that electromagnetically induced transparency can be achieved in metamaterials, in which electromagnetic radiation is interacting resonantly with mesoscopic oscillators rather than with atoms. We describe novel metamaterial designs that can support a full dark resonant state upon interaction with an electromagnetic beam and we present results of its frequency-dependent effective permeability and permittivity. These results, showing a transparency window with extremely low absorption and strong dispersion, are confirmed by accurate simulations of the electromagnetic field propagation in the metamaterial.
620 citations
TL;DR: In this paper, an Ag split ring resonator (SRR) is patterned with e-beam lithography onto planar VO_2 and etched via reactive ion etching to yield Ag/VO_2 hybrid SRRs.
Abstract: Engineering metamaterials with tunable resonances from mid-infrared to near-infrared wavelengths could have far-reaching consequences for chip based optical devices, active filters, modulators, and sensors. Utilizing the metal-insulator phase transition in vanadium oxide (VO_2), we demonstrate frequency-tunable metamaterials in the near-IR range, from 1.5 - 5 microns. Arrays of Ag split ring resonators (SRRs) are patterned with e-beam lithography onto planar VO_2 and etched via reactive ion etching to yield Ag/VO_2 hybrid SRRs. FTIR reflection data and FDTD simulation results show the resonant peak position red shifts upon heating above the phase transition temperature. We also show that, by including coupling elements in the design of these hybrid Ag/VO_2 bi-layer structures, we can achieve resonant peak position tuning of up to 110 nm.
511 citations
TL;DR: Here it is shown that transformation optics of a curved, non-Euclidean space (such as the surface of a virtual sphere) relax these requirements and can lead to invisibility in a broad band of the spectrum.
Abstract: Invisibility and negative refraction are both applications of transformation optics where the material of a device performs a coordinate transformation for electromagnetic fields. The device creates the illusion that light propagates through empty flat space, whereas in physical space, light is bent around a hidden interior or seems to run backward in space or time. All of the previous proposals for invisibility require materials with extreme properties. Here we show that transformation optics of a curved, non-Euclidean space (such as the surface of a virtual sphere) relax these requirements and can lead to invisibility in a broad band of the spectrum.
468 citations
Book•
16 Nov 2009
TL;DR: Theory, design, and applications of metamaterials go beyond left-handed materials (LHM) or negative index materials (NIM) and focus on recent research activity as mentioned in this paper.
Abstract: Metamaterials:Theory, Design, and Applications goes beyond left-handed materials (LHM) or negative index materials (NIM) and focuses on recent research activity. Included here is an introduction to optical transformation theory, revealing invisible cloaks, EM concentrators, beam splitters, and new-type antennas, a presentation of general theory on artificial metamaterials composed of periodic structures, coverage of a new rapid design method for inhomogeneous metamaterials, which makes it easier to design a cloak, and new developments including but not limited to experimental verification of invisible cloaks, FDTD simulations of invisible cloaks, the microwave and RF applications of metamaterials, sub-wavelength imaging using anisotropic metamaterials, dynamical metamaterial systems, photonic metamaterials, and magnetic plasmon effects of metamaterials.
342 citations
TL;DR: In this paper, the authors link the newly emerged field of artificial optical materials to that of celestial mechanics, thus opening the way to investigate light phenomena reminiscent of orbital motion, strange attractors and chaos, in a controlled laboratory environment.
Abstract: Einstein’s general theory of relativity establishes equality between matter–energy density and the curvature of spacetime. As a result, light and matter follow natural paths in the inherent spacetime and may experience bending and trapping in a specific region of space. So far, the interaction of light and matter with curved spacetime has been predominantly studied theoretically and through astronomical observations. Here, we propose to link the newly emerged field of artificial optical materials to that of celestial mechanics, thus opening the way to investigate light phenomena reminiscent of orbital motion, strange attractors and chaos, in a controlled laboratory environment. The optical–mechanical analogy enables direct studies of critical light/matter behaviour around massive celestial bodies and, on the other hand, points towards the design of novel optical cavities and photon traps for application in microscopic devices and lasers systems. Black holes are difficult to study experimentally, owing to their distance from us and indeed their very nature. A theoretical study suggests that optical metamaterials that exhibit behaviour that is reminiscent of that of black holes, could enable us to learn more about these and other astrophysical objects.
340 citations
Book•
05 Oct 2009
TL;DR: In this paper, C.R. Simovski and S.A. Sihvola proposed a method for modeling and modeling of metamaterials, based on the method of moments for artificial materials.
Abstract: Part I: General Concepts Historical Notes on Metamaterials, C.R. Simovski and S.A. Tretyakov Material Parameters and Field Energy in Reciprocal Composite Media, C.R. Simovski and S.A. Tretyakov Symmetry Principles and Group-Theoretical Methods in Electromagnetics of Complex Media, V. Dmitriev Differential Forms and Electromagnetic Materials, I. V. Lindell Part II: Modeling Principles of Metamaterials Fundamentals of Method of Moments for Artificial Materials, C. Craeye, X. Radu, F. Capolino, and A. G. Schuchinsky FDTD Method for Periodic Structures, J. Chen, F. Yang, and R. Qiang Polarizability of Simple-Shaped Particles, A. Sihvola Single Dipole Approximation for Modeling Collections of Nanoscatterers, S. Steshenko and F. Capolino Mixing Rules, A. Sihvola Nonlocal Homogenization Theory of Structured Materials, M. G. Silveirinha On the Extraction of LocalMaterial Parameters of Meta-Materials from Experimental or Simulated Data, C. R. Simovski Field Representations in Periodic Artificial Materials Excited by a Source, F. Capolino, D. R. Jackson, and D. R. Wilton Modal Properties of Layered Metamaterials, P. Baccarelli, P. Burghignoli, A. Galli, P. Lampariello, G. Lovat, S. Paulotto, and G. Valerio Part III: Artificial Magnetics and Dielectrics, Negative Index Media RF Metamaterials, M. C. K. Wiltshire Wire Media, I. S. Nefedov and A. J. Viitanen Split Ring Resonators and Related Topologies, R. Marques and F. Martin Designing One-, Two-, and Three-Dimensional Left-Handed Materials, M. Kafesaki, Th. Koschny, C. M. Soukoulis, and E. N. Economou Composite Metamaterials, Negative Refraction and Focusing, E. Ozbay and K. Aydin Metamaterials Based on Pairs of Tightly Coupled Scatterers, A. Vallecchi and F. Capolino Theory and Design of Metamorphic Materials, C. A. Kyriazidou,H. F. Contopanagos, and N. G. Alexopoulos Isotropic Double Negative Materials, I. Vendik, O. G. Vendik, and M. Odit Network Topology Derived Metamaterials: Scalar and Vectorial 3-D Configurations and Their Fabrication, P. Russer and M. Zedler Negative Refraction in IR and Visible Domains, A. Alu and N. Engheta Part IV: Artificial Chiral, Bianisotropic Media, and Quasicrystals A Review of Chiral and Bianisotropic Composite Materials Providing Backward Waves and Negative Refractive Indices, C.-W. Qiu, S. Zouhdi, and A. Sihvola Negative Refraction and Perfect Lenses Using Chiral and Bianisotropic Materials, S.A. Tretyakov Bianisotropic Materials and PEMC, A. Sihvola and I. V. Lindell Photonic Quasicrystals: Basics and Examples, A. Della Villa, V. Galdi, F. Capolino, S. Enoch, and G. Tayeb Part V: Transmission-Line-Based Metamaterials Fundamentals of Transmission-LineMetamaterials, A. K. Iyer and G. V. Eleftheriades Corrugated RectangularWaveguides: Composite Right/Left-Handed Metaguides, I. A. Eshrah, A. A. Kishk, A. B. Yakovlev, and A. W. Glisson Part VI: Artificial Surfaces Frequency Selective Surface and Electromagnetic Bandgap Theory Basics, J. C. Vardaxoglou, R. Lee, and A. Chauraya High-Impedance Surfaces, G. Goussetis, A. P. Feresidis, A. B. Yakovlev, and C. R. Simovski Part VII: Tunable and Nonlinear Metamaterials Tunable Surfaces: Modeling and Realizations, C. Panagamuwa and Y. Vardaxoglou Ferroelectrics as Constituents of Tunable Metamaterials, O. G. Vendik and S. P. Zubko Spin Waves in Multilayered and Patterned Magnetic Structures, N. Grigorieva, B. Kalinikos, M. Kostylev, and A. Stashkevich Nonlinear Metamaterials, M. Lapine and M. Gorkunov Magnetoinductive Waves I: Theory, O. Sydoruk, O. Zhuromskyy, A. Radkovskaya, E. Shamonina, and L. Solymar
TL;DR: In this article, the geometry of light and the concepts of transformation optics are described and connections between geometry and electromagnetism in media that is as consistent and elementary as possible.
Abstract: Publisher Summary This chapter describes the geometry of light and the concepts of transformation optics. Transformation optics is beginning to transform optics. The chapter introduces connections between geometry and electromagnetism in media that is as consistent and elementary as possible. This chapter analyzes four examples of transformation media—cloaking devices, perfect lenses, vortices, and horizons; these four cases illustrate characteristic non-trivial topologies, each one with different physics, and they have been experimentally verified. This chapter focuses on the main ideas and some connections between optics, in particular, transformation optics, and other areas of physics and mathematics. It also addresses the classical optics of transformation media.
TL;DR: In this article, the wave propagation properties of chiral metamaterials were studied and negative refraction was demonstrated in 3D isotropic chirality, with neither negative nor negative μ negative required.
Abstract: Electromagnetic metamaterials are composed of periodically arranged artificial structures. They show peculiar properties, such as negative refraction and super-lensing, which are not seen in natural materials. The conventional metamaterials require both negativeand negative μ to achieve negative refraction. Chiral metamaterial is a new class of metamaterials offering a simpler route to negative refraction. In this paper, we briefly review the history of metamaterials and the developments on chiral metamaterials. We study the wave propagation properties in chiral metamaterials and show that negative refraction can be realized in chiral metamaterials with a strong chirality, with neithernor μ negative required. We have developed a retrieval procedure, adopting a uniaxial bi-isotropic model to calculate the effective parameters such as n±, κ, � and μ of the chiral metamaterials. Our work on the design, numerical calculations and experimental measurements of chiral metamaterials is introduced. Strong chiral behaviors such as optical activity and circular dichroism are observed and negative refraction is obtained for circularly polarized waves in these chiral metamaterials. We show that 3D isotropic chiral metamaterials can eventually be realized.
TL;DR: Recent theoretical and experimental progress on making objects invisible to detection by electromagnetic waves is described and ideas for devices that would once have seemed fanciful may now be at least approximately implemented physically using a new class of artificially structured materials called metamaterials.
Abstract: We describe recent theoretical and experimental progress on making objects invisible to detection by electromagnetic waves. Ideas for devices that would once have seemed fanciful may now be at least approximately implemented physically using a new class of artificially structured materials called metamaterials. Maxwell's equations have transformation laws that allow for the design of electromagnetic material parameters that steer light around a hidden region, returning it to its original path on the far side. Not only would observers be unaware of the contents of the hidden region, they would not even be aware that something was being hidden. An object contained in the hidden region, which would have no shadow, is said to be cloaked. Proposals for, and even experimental implementations of, such cloaking devices have received the most attention, but other designs having striking effects on wave propagation are possible. All of these designs are initially based on the transformation laws of the equations that govern wave propagation but, due to the singular parameters that give rise to the desired effects, care needs to be taken in formulating and analyzing physically meaningful solutions. We recount the recent history of the subject and discuss some of the mathematical and physical issues involved.
TL;DR: In this article, a theory of the homogenization of a certain class of metamaterials is stated, and a more widespread method of determining the material parameters of met amaterials based on the extraction of the refractive index and the characteristic impedance from the scattering matrix of the plate of the metammaterial is discussed.
Abstract: A theory of the homogenization of a certain class of metamaterials is stated. These metamaterials are volume lattices of electric and magnetic dipoles that are resonant with frequencies that are considerably lower than that of the first Bragg resonance of the lattice. It was shown that, for plates of a metamaterial, which are described by bulk material parameters, transition layers play an important role, and the known Drude notion of transition layers is significantly revised. The paper also discusses a more widespread method of determining the material parameters of metamaterials based on the extraction of the refractive index and the characteristic impedance from the scattering matrix of the plate of the metamaterial. The physical meaning of the material parameters obtained in this way is clarified, and the concept of Bloch lattices related to it is discussed. It is shown that the bulk material parameters and the parameters of transition layers can also be extracted from components of the scattering matrix of plates.
TL;DR: An omnidirectional retroreflector is demonstrated, a device for faithfully reflecting images and for creating high visibility from all directions, that would normally require a dielectric singularity, an infinity in the refractive index in a real metamaterial.
Abstract: Transformation optics is a concept used in some metamaterials to guide light on a predetermined path. In this approach, the materials implement coordinate transformations on electromagnetic waves to create the illusion that the waves are propagating through a virtual space. Transforming space by appropriately designed materials makes devices possible that have been deemed impossible. In particular, transformation optics has led to the demonstration of invisibility cloaking for microwaves, surface plasmons and infrared light. Here, on the basis of transformation optics, we implement a microwave device that would normally require a dielectric singularity, an infinity in the refractive index. To fabricate such a device, we transmute a dielectric singularity in virtual space into a mere topological defect in a real metamaterial. In particular, we demonstrate an omnidirectional retroreflector, a device for faithfully reflecting images and for creating high visibility from all directions. Our method is robust, potentially broadband and could also be applied to visible light using similar techniques.
TL;DR: In this paper, a planar design of a metamaterial exhibiting electromagnetically induced transparency was presented, which is amenable to experimental verification in the microwave frequency band, based on the coupling of a split-ring resonator with a cut-wire in the same plane.
Abstract: We present a planar design of a metamaterial exhibiting electromagnetically induced transparency that is amenable to experimental verification in the microwave frequency band. The design is based on the coupling of a split-ring resonator with a cut-wire in the same plane. We investigate the sensitivity of the parameters of the transmission window on the coupling strength and on the circuit elements of the individual resonators, and we interpret the results in terms of two linearly coupled Lorentzian resonators. Our metamaterial designs combine low losses with the extremely small group velocity associated with the resonant response in the transmission window, rendering them suitable for slow light applications at room temperature.
TL;DR: In this article, the authors demonstrate experimentally and numerically that nonplanar chiral metamaterials give giant optical activity, circular dichroism, and negative refractive index.
Abstract: We demonstrate experimentally and numerically that nonplanar chiral metamaterials give giant optical activity, circular dichroism, and negative refractive index. The transmission, reflection, and the retrieval results of the experiments agree pretty well with the simulations. This is an important step toward the design and fabrication of three-dimensional isotropic chiral metamaterials.
TL;DR: Using transformation optics a frequency-selective superabsorber can be constructed that consists of an absorbing core material coated with a shell of isotropic double negative metamaterial that serves to amplify the evanescent tail of the high-order cylindrical waves.
Abstract: Using transformation optics a frequency-selective superabsorber can be constructed that consists of an absorbing core material coated with a shell of isotropic double negative metamaterial. For a fixed volume its absorption cross section can be made arbitrarily large at one frequency. The double-negative shell serves to amplify the evanescent tail of the high-order cylindrical waves, which induces strong scattering and absorption. Our conclusion is supported by both analytical Mie theory and numerical finite-element simulation. Interesting applications of such a device are discussed.
TL;DR: Though transformation optical media are generally anisotropic, with both electric and magnetic response, it is possible to arrive at a dielectric-only transformation optical distribution for a lens interacting with transverse-magnetic (TM) polarized light.
Abstract: Transformation optics is widely associated with the design of unconventional electromagnetic devices, such as electromagnetic cloaks or concentrators. However, a wide range of conventional optical devices with potentially advantageous properties can be designed by the transformation optical approach. For example, a coordinate transformation can be introduced that compresses a region of space, resulting in an overall decrease in the thickness of an optical instrument such as a lens. The optical properties of a transformed lens, such as Fresnel reflection or aberration profile, are equivalent to those of the original lens, while the transformed lens and the bounding transformation optical material are thinner than the original lens. This approach to flattening the profile of a lens represents an advantage over the use of a higher dielectric material because it does not introduce greater Fresnel reflections or require a redesign of the basic optic. Though transformation optical media are generally anisotropic, with both electric and magnetic response, it is possible to arrive at a dielectric-only transformation optical distribution for a lens interacting with transverse-magnetic (TM) polarized light. The dielectric-only distribution can be implemented using broad-band, low-loss metamaterials. Lens designs for both a full transformation and a dielectric-only implementation are discussed and confirmed via finite-element simulations.
TL;DR: The permittivity and permeability tensors in the transformed space are found to correlate with the deformation field of the material and can be easily extended to design other transformation materials for electromagnetic and acoustic wave phenomena.
Abstract: In transformation optics, the space transformation is viewed as the deformation of a material. The permittivity and permeability tensors in the transformed space are found to correlate with the deformation field of the material. By solving the Laplace’s equation, which describes how the material will deform during a transformation, we can design electromagnetic cloaks with arbitrary shapes if the boundary conditions of the cloak are considered. As examples, the material parameters of the spherical and elliptical cylindrical cloaks are derived based on the analytical solutions of the Laplace’s equation. For cloaks with irregular shapes, the material parameters of the transformation medium are determined numerically by solving the Laplace’s equation. Full-wave simulations based on the Maxwell’s equations validate the designed cloaks. The proposed method can be easily extended to design other transformation materials for electromagnetic and acoustic wave phenomena.
TL;DR: This method combines the novel effects of TO with the practicality of all-dielectric construction to create reflection less, inherently isotropic, and broadband photonic devices that are capable of guiding light in almost arbitrary fashion over an unprecedented range of frequencies.
Abstract: The past decade has seen a revolution in electromagnetics due to the development of metamaterials. These artificial composites have been fashioned to exhibit exotic effects such as a negative index of refraction. However, the full potential of metamaterial devices has only been hinted at. By combining metamaterials with transformation optics (TO), researchers have demonstrated an invisibility cloak. Subsequently, quasi-conformal mapping was used to create a device that exhibited a broadband cloaking effect. Here we extend this latter approach to a strictly conformal mapping to create reflection less, inherently isotropic, and broadband photonic devices. Our method combines the novel effects of TO with the practicality of all-dielectric construction. We show that our structures are capable of guiding light in an almost arbitrary fashion over an unprecedented range of frequencies.
TL;DR: In this article, the authors demonstrate experimentally and theoretically dielectric metamaterials exhibiting a tunable range of negative effective permeability in the terahertz spectral region 0.2 -0.36 THz.
Abstract: We demonstrate experimentally and theoretically dielectric metamaterials exhibiting a tunable range of negative effective permeability in the terahertz spectral region 0.2–0.36 THz. Our structures consist of an array of intrinsically nonmagnetic rods made of an incipient ferroelectric SrTiO3 which shows a high tunable permittivity. The magnetic response and its tuning are achieved by a temperature control of the permittivity of SrTiO3, which defines the resonant confinement of the electromagnetic field within the rods.
TL;DR: This work implemented a new invisibility cloak using an array of silicon nanorods fabricated by electron-beam lithography, and directly visualized the cloaking effect by monitoring the light propagation inside the device using the near-field optical microscopy.
Abstract: A new invisibility cloak was recently proposed for hiding objects in front of a highly reflecting mirror. This cloak requires only modest values of optical constants with minimal anisotropy and thus can be implemented by using non-resonant dielectric materials, making it an ideal system for optical frequency operation. We implemented the cloak using an array of silicon nanorods fabricated by electron-beam lithography. We then directly visualized the cloaking effect by monitoring the light propagation inside the device using the near-field optical microscopy.
TL;DR: The first experimental demonstration of broadband and low-loss directive free-space cloak and compact-sized carpet cloak realized using non-resonant metamaterials in the microwave frequency represents a major step towards the real applications of invisibility cloaks.
Abstract: Recently, invisible cloaks have attracted much attention due to their exciting property of invisibility, which are based on a solid theory of transformation optics and quasi-conformal mapping. Two kinds of cloaks have been proposed: free-space cloaks, which can render objects in free space invisible to incident radiation, and carpet cloaks (or ground-plane cloaks), which can hide objects under the conducting ground. The first free-space and carpet cloaks were realized in the microwave frequencies using metamaterials. The free-space cloak was composed of resonant metamaterials, and hence had restriction of narrow bandwidth and high loss; the carpet cloak was made of non-resonant metamaterials, which have broad bandwidth and low loss. However, the carpet cloak has a severe restriction of large size compared to the cloaked object. The above restrictions become the bottlenecks to the real applications of free-space and carpet cloaks. Here we report the first experimental demonstration of broadband and low-loss directive free-space cloak and compact-sized carpet cloak based on a recent theoretical study. Both cloaks are realized using non-resonant metamaterials in the microwave frequency, and good invisibility properties have been observed in experiments. This approach represents a major step towards the real applications of invisibility cloaks.
TL;DR: In this paper, a model of an infrared metamaterial absorber composed of metal dendritic resonators, dielectric substrate, and continuous metal film is presented, and numerical simulation confirms an absorptivity of 98.6% at the infrared wavelength of 2.79 μm.
Abstract: We present a model of an infrared metamaterial absorber composed of metal dendritic resonators, dielectric substrate, and continuous metal film. Numerical simulation confirms an absorptivity of 98.6% at the infrared wavelength of 2.79 μm. The proposed metamaterial absorber has an excellence of two-dimensional isotropy, and it could be fabricated with a chemical double-template technique. Our simulation shows it could be operated for a wide range of incident angles. The optical metamaterial absorber proposed in this paper has potential applications such as in infrared imaging devices, thermal bolometers, and wavelength-selective radiators.
TL;DR: The inverse Laplace's equation with sliding boundary condition is proposed for quasi-isotropic transformation material design and is very simple compared with other quasi-conformal methods based on grid generation tools.
Abstract: The deformation method of transformation optics has been demonstrated to be a useful tool, especially in designing arbitrary and nonsingular transformation materials. Recently, there are emerging demands for isotropic material parameters, arising from the broadband requirement of the designed devices. In this work, the deformation method is further developed to design quasi-isotropic/isotropic transformation materials. The variational functional of the inverse Laplace's equation is investigated and found to involve the smooth and quasi-conformal nature of coordinate transformation. Together with the sliding boundary conditions, the inverse Laplace's equation can be utilized to give transformations which are conformal or quasi-conformal, depending on functionalities of interest. Examples of designing an arbitrary carpet cloak and a waveguide with arbitrary cross sections are given to validate the proposed idea. Compared with other quasi-conformal methods based on grid generation tools, the proposed method unifies the design and validation of transformation devices, and thus is much convenient.
TL;DR: Utilizing non-resonant metamaterial elements, it is demonstrated that complex gradient index optics can be constructed exhibiting low material losses and large frequency bandwidth.
Abstract: Utilizing non-resonant metamaterial elements, we demonstrate that complex gradient index optics can be constructed exhibiting low material losses and large frequency bandwidth. Although the range of structures is limited to those having only electric response, with an electric permittivity always equal to or greater than unity, there are still numerous metamaterial design possibilities enabled by leveraging the non-resonant elements. For example, a gradient, impedance matching layer can be added that drastically reduces the return loss of the optical elements due to reflection. In microwave experiments, we demonstrate the broadband design concepts with a gradient index lens and a beam-steering element, both of which are confirmed to operate over the entire X-band (roughly 8-12 GHz) frequency spectrum.
TL;DR: Two-dimensional far-zone focusing lenses are designed using the coordinate transformation approach that feature minimized reflections from the lens boundaries that are verified using a full-wave finite-element analysis and compared with previously reported transformation optical lenses.
Abstract: Two-dimensional far-zone focusing lenses are designed using the coordinate transformation approach that feature minimized reflections from the lens boundaries. A flat lens of trapezoidal cross section completely converts incident waves with cylindrical wavefronts into transmitted waves with planar wavefronts. A rectangular lens with reduced non-magnetic material parameters that incorporates a nonlinear coordinate transformation features a significantly reduced amount of reflections compared with the non-magnetic lens based on a linear transformation. The improved reflection performance of each new lens design is verified using a full-wave finite-element analysis and compared with previously reported transformation optical lenses.
TL;DR: In this article, the authors derived the permeability and permittivity tensors of a metamaterial able to transform an isotropically radiating source into a compact ultradirective antenna in the microwave domain.
Abstract: Spatial coordinate transformation is used as a reliable tool to control electromagnetic fields. In this paper, we derive the permeability and permittivity tensors of a metamaterial able to transform an isotropically radiating source into a compact ultradirective antenna in the microwave domain. We show that the directivity of this antenna is competitive with regard to conventional directive antennas horn and reflector antennas, besides its dimensions are smaller. Numerical simulations using finite element method are performed to illustrate these properties. A reduction in the electromagnetic material parameters is also proposed for an easy fabrication of this antenna from existing materials. Following that, the design of the proposed antenna using a layered metamaterial is presented. The different layers are all composed of homogeneous and uniaxial anisotropic metamaterials, which can be obtained from simple metal-dielectric structures. When the radiating source is embedded in the layered metamaterial, a highly directive beam is radiated from the antenna