Showing papers on "Metamaterial published in 2008"
TL;DR: This work fabricate, characterize, and analyze a MM absorber with a slightly lower predicted A(omega) of 96%.
Abstract: We present the design for an absorbing metamaterial (MM) with near unity absorbance A(omega). Our structure consists of two MM resonators that couple separately to electric and magnetic fields so as to absorb all incident radiation within a single unit cell layer. We fabricate, characterize, and analyze a MM absorber with a slightly lower predicted A(omega) of 96%. Unlike conventional absorbers, our MM consists solely of metallic elements. The substrate can therefore be optimized for other parameters of interest. We experimentally demonstrate a peak A(omega) greater than 88% at 11.5 GHz.
5,550 citations
TL;DR: A plasmonic "molecule" consisting of a radiative element coupled with a subradiant (dark) element is theoretically investigated and shows electromagnetic response that closely resembles the electromagnetically induced transparency in an atomic system.
Abstract: A plasmonic "molecule" consisting of a radiative element coupled with a subradiant (dark) element is theoretically investigated. The plasmonic molecule shows electromagnetic response that closely resembles the electromagnetically induced transparency in an atomic system. Because of its subwavelength dimension, this electromagnetically induced transparency-like molecule can be used as a building block to construct a "slow light" plasmonic metamaterial.
2,088 citations
TL;DR: Bulk optical metamaterials open up prospects for studies of 3D optical effects and applications associated with NIMs and zero-index materials such as reversed Doppler effect, superlenses, optical tunnelling devices, compact resonators and highly directional sources.
Abstract: Metamaterials are artificially engineered structures that have properties, such as a negative refractive index, not attainable with naturally occurring materials. Negative-index metamaterials (NIMs) were first demonstrated for microwave frequencies, but it has been challenging to design NIMs for optical frequencies and they have so far been limited to optically thin samples because of significant fabrication challenges and strong energy dissipation in metals. Such thin structures are analogous to a monolayer of atoms, making it difficult to assign bulk properties such as the index of refraction. Negative refraction of surface plasmons was recently demonstrated but was confined to a two-dimensional waveguide. Three-dimensional (3D) optical metamaterials have come into focus recently, including the realization of negative refraction by using layered semiconductor metamaterials and a 3D magnetic metamaterial in the infrared frequencies; however, neither of these had a negative index of refraction. Here we report a 3D optical metamaterial having negative refractive index with a very high figure of merit of 3.5 (that is, low loss). This metamaterial is made of cascaded 'fishnet' structures, with a negative index existing over a broad spectral range. Moreover, it can readily be probed from free space, making it functional for optical devices. We construct a prism made of this optical NIM to demonstrate negative refractive index at optical frequencies, resulting unambiguously from the negative phase evolution of the wave propagating inside the metamaterial. Bulk optical metamaterials open up prospects for studies of 3D optical effects and applications associated with NIMs and zero-index materials such as reversed Doppler effect, superlenses, optical tunnelling devices, compact resonators and highly directional sources.
2,025 citations
TL;DR: A metamaterial that acts as a strongly resonant absorber at terahertz frequencies using a bilayer unit cell which allows for maximization of the absorption through independent tuning of the electrical permittivity and magnetic permeability is presented.
Abstract: We present a metamaterial that acts as a strongly resonant absorber at terahertz frequencies. Our design consists of a bilayer unit cell which allows for maximization of the absorption through independent tuning of the electrical permittivity and magnetic permeability. An experimental absorptivity of 70% at 1.3 terahertz is demonstrated. We utilize only a single unit cell in the propagation direction, thus achieving an absorption coefficient α=2000 cm-1. These metamaterials are promising candidates as absorbing elements for thermally based THz imaging, due to their relatively low volume, low density, and narrow band response.
1,247 citations
TL;DR: Bulk metamaterials made of nanowires that show negative refraction for all incident angles in the visible region are reported, resulting in a low-loss and a broad-band propagation at visible frequencies.
Abstract: Negative refraction in metamaterials has generated great excitement in the scientific community. Although negative refraction has been realized in microwave and infrared by using metamaterials and by using two-dimensional waveguide structures, creation of a bulk metamaterial showing negative refraction at visible frequency has not been successful, mainly because of the significant resonance losses and fabrication difficulties. We report bulk metamaterials made of nanowires that show such negative refraction for all incident angles in the visible region. Moreover, the negative refraction occurs far from any resonance, resulting in a low-loss and a broad-band propagation at visible frequencies. These remarkable properties can substantially affect applications such as imaging, three-dimensional light manipulation, and optical communication.
843 citations
TL;DR: In this article, the authors present the experimental realization and theoretical understanding of a membrane-type acoustic metamaterial with very simple construct, capable of breaking the mass density law of sound attenuation in the 100-1000 Hz regime by a significant margin.
Abstract: We present the experimental realization and theoretical understanding of a membrane-type acoustic metamaterial with very simple construct, capable of breaking the mass density law of sound attenuation in the 100--1000 Hz regime by a significant margin ($\ensuremath{\sim}200$ times). Owing to the membrane's weak elastic moduli, there can be low-frequency oscillation patterns even in a small elastic film with fixed boundaries defined by a rigid grid. The vibrational eigenfrequencies can be tuned by placing a small mass at the center of the membrane sample. Near-total reflection is achieved at a frequency between two eigenmodes where the in-plane average of normal displacement is zero. By using finite element simulations, negative dynamic mass is explicitly demonstrated at frequencies around the total reflection frequency. Excellent agreement between theory and experiment is obtained.
810 citations
04 May 2008
TL;DR: In this paper, the interaction between adjacent stacked layers using the method of plasmon hybridization was investigated, and the optical properties of stacked metamaterials with increasing layer numbers were analyzed.
Abstract: We experimentally demonstrate the implementation of three-dimensional optical metamaterials. We investigate the interaction between adjacent stacked layers using the method of plasmon hybridization and analyze the optical properties of stacked metamaterials with increasing layer numbers.
804 citations
TL;DR: In this paper, the authors demonstrate frequency-agile terahertz metamaterials operating in the far-infrared by incorporating semiconductors in critical regions of metallic split-ring resonators.
Abstract: Metamaterials exhibit numerous novel effects1,2,3,4,5 and operate over a large portion of the electromagnetic spectrum6,7,8,9,10. Metamaterial devices based on these effects include gradient-index lenses11,12, modulators for terahertz radiation13,14,15 and compact waveguides16. The resonant nature of metamaterials results in frequency dispersion and narrow bandwidth operation where the centre frequency is fixed by the geometry and dimensions of the elements comprising the metamaterial composite. The creation of frequency-agile metamaterials would extend the spectral range over which devices function and, further, enable the manufacture of new devices such as dynamically tunable notch filters. Here, we demonstrate such frequency-agile metamaterials operating in the far-infrared by incorporating semiconductors in critical regions of metallic split-ring resonators. For this first-generation device, external optical control results in tuning of the metamaterial resonance frequency by ∼20%. Our approach is integrable with current semiconductor technologies and can be implemented in other regions of the electromagnetic spectrum. Metamaterials that possess frequency tunability enable new device functions. By external optical control through the incorporation of semiconductors in metallic split-ring resonators, the researchers provide an elegant solution to frequency-agile terahertz metamaterials.
787 citations
TL;DR: It is shown that pulses propagating through such metamaterials experience considerable delay, and the thickness of the structure along the direction of wave propagation is much smaller than the wavelength, which allows successive stacking of multiple meetamaterial slabs leading to increased transmission and bandwidth.
Abstract: We demonstrate a classical analog of electromagnetically induced transparency in a planar metamaterial. We show that pulses propagating through such metamaterials experience considerable delay. The thickness of the structure along the direction of wave propagation is much smaller than the wavelength, which allows successive stacking of multiple metamaterial slabs leading to increased transmission and bandwidth.
775 citations
TL;DR: In this article, a square electromagnetic cloak and an omni-directional electromagnetic field concentrator are described and the functionality of the devices is numerically confirmed by two-dimensional finite element simulations.
Abstract: The technique of applying form-invariant, spatial coordinate transformations of Maxwell’s equations can facilitate the design of structures with unique electromagnetic or optical functionality. Here, we illustrate the transformation-optical approach in the designs of a square electromagnetic cloak and an omni-directional electromagnetic field concentrator. The transformation equations are described and the functionality of the devices is numerically confirmed by two-dimensional finite element simulations. The two devices presented demonstrate that the transformation optic approach leads to the specification of complex, anisotropic and inhomogeneous materials with well directed and distinct electromagnetic behavior.
770 citations
19 Oct 2008
TL;DR: In this paper, the authors demonstrate THz metamaterials exhibiting either amplitude control via carrier injection or depletion in the active semiconductor substrate or frequency control via photoexcitation of carriers into active semiconducting materials incorporated into the sub-wavelength metammaterial structure.
Abstract: We demonstrate THz metamaterials exhibiting either amplitude control, via carrier injection or depletion in the active semiconductor substrate or frequency control, via photoexcitation of carriers into active semiconducting materials incorporated into the sub-wavelength metamaterial structure.
TL;DR: This recently developed theory of energy squeezing and tunneling is experimentally verified through an ultranarrow waveguide channel that mimics zero-permittivity properties, showing an almost uniform phase along the narrow channel and weak dependence over its geometry.
Abstract: Utilizing a microwave setup, we experimentally verify our recently developed theory of energy squeezing and tunneling [Phys. Rev. Lett. 97, 157403 (2006)] through an ultranarrow waveguide channel that mimics zero-permittivity properties. Exploiting the infinite phase velocity supported by a waveguide transition section at cutoff, we test our theory of tunneling in this zero-permittivity region without use of resonant inclusions. This ``supercoupling'' is shown to have unique anomalous properties: an almost uniform phase along the narrow channel and weak dependence over its geometry.
TL;DR: In this article, a planar narrow-diversion coherent source of electromagnetic radiation that is fuelled by plasmonic oscillations is proposed. But the spaser concept is not considered in this paper.
Abstract: In 2003 Bergman and Stockman introduced the spaser, a quantum amplifier of surface plasmons by stimulated emission of radiation. They argued that, by exploiting a metal/dielectric composite medium, it should be possible to construct a nano-device, where a strong coherent field is built up in a spatial region much smaller than the wavelength. It was suggested that V-shaped metallic inclusions, combined with a collection of semiconductor quantum dots could lead to a realization of the spaser. Here we introduce a further development of the spaser concept. We show that by combining the metamaterial and spaser ideas one can create a planar narrow-diversion coherent source of electromagnetic radiation that is fuelled by plasmonic oscillations. We argue that two-dimensional arrays of a certain class of plasmonic resonators supporting high-Q current excitations belong to a new category of coherent metamaterials that provide an intriguing opportunity to create a spatially and temporally coherent laser source, the Lasing Spaser.
TL;DR: In this article, the authors report direct measurements of the propagation and confinement of terahertz electromagnetic surface modes tightly bound to flat plasmonic metamaterials that consist of metal surfaces decorated with two-dimensional arrays of subwavelength-periodicity pits.
Abstract: Metamaterials are artificial materials with subwavelength structure1 that enable the translation of magnetic2 and electric responses3 into spectral regions not accessible through naturally occurring materials. Here, we report direct measurements of the propagation and confinement of terahertz electromagnetic surface modes tightly bound to flat plasmonic metamaterials that consist of metal surfaces decorated with two-dimensional arrays of subwavelength-periodicity pits. These modes are surface plasmon polaritons with an effective plasma frequency controlled entirely by the surface geometry4. The mode spectrum and penetration depth into air demonstrate strong wavelength-scale energy confinement to the surface below the electromagnetic band edge; this is in stark contrast to the very weak confinement found at flat metal surfaces in this spectral regime. The results are in good agreement with analytical and numerical models of surface plasmon polaritons propagating on structured perfect-conductor surfaces, and imply that plasmonic metamaterials could help miniaturize optical components or lead to improved chemical or biochemical sensors.
TL;DR: The limiting effects of varying the thickness of a dielectric overlayer on planar double split-ring resonator (SRR) arrays are studied by terahertz time-domain spectroscopy and the bounds of resonance shifting are discussed.
Abstract: The limiting effects of varying the thickness of a dielectric overlayer on planar double split-ring resonator (SRR) arrays are studied by terahertz time-domain spectroscopy. Uniform dielectric overlayers from 100 nm to 16 µm thick are deposited onto fixed SRR arrays in order to shift the resonance frequency of the electric response. We discuss the bounds of resonance shifting and emphasize the resulting limitations for SRR-based sensing. These results are presented in the context of typical biosensing situations and are compared to previous work and other existing sensing platforms.
TL;DR: An experimental demonstration of microwave tunneling between two planar waveguides separated by a thin ENZ channel is presented, in agreement with theory and numerical simulations.
Abstract: Silveirinha and Engheta have recently proposed that electromagnetic waves can tunnel through a material with an electric permittivity ($ϵ$) near zero (ENZ). An ENZ material of arbitrary geometry can thus serve as a perfect coupler between incoming and outgoing waveguides with identical cross-sectional area, so long as one dimension of the ENZ is electrically small. In this Letter we present an experimental demonstration of microwave tunneling between two planar waveguides separated by a thin ENZ channel. The ENZ channel consists of a planar waveguide in which complementary split ring resonators are patterned on the lower surface. A tunneling passband is found in transmission measurements, while a two-dimensional spatial map of the electric field distribution reveals a uniform phase variation across the channel---both measurements in agreement with theory and numerical simulations.
Patent•
17 Mar 2008
TL;DR: In this article, the authors present an approach for using composite left and right handed (CRLH) metamaterial (MTM) structure antenna elements and arrays to provide radiation pattern shaping and beam switching.
Abstract: Apparatus, systems and techniques for using composite left and right handed (CRLH) metamaterial (MTM) structure antenna elements and arrays to provide radiation pattern shaping and beam switching.
TL;DR: In this paper, the authors proposed a multilayered composite made of two types of isotropic acoustic metamaterials, whose elastic parameters should be properly chosen in order to satisfy (in the homogenization limit) the acoustic properties under request.
Abstract: This work proposes an acoustic structure feasible to engineer that accomplishes the requirements of acoustic cloaking design recently introduced by Cummer and Schurig (2007 New J. Phys. 9 45). The structure, which consists of a multilayered composite made of two types of isotropic acoustic metamaterials, exactly matches the conditions for the acoustic cloaking. It is also shown that the isotropic metamaterials needed can be made of sonic crystals containing two types of material cylinders, whose elastic parameters should be properly chosen in order to satisfy (in the homogenization limit) the acoustic properties under request. In contrast to electromagnetic cloaking, the structure here proposed verifies the acoustic cloaking in a wide range of wavelengths; its performance is guaranteed for any wavelength above a certain cutoff defined by the homogenization limit of the sonic crystal employed in its fabrication.
TL;DR: In this paper, the authors present an overview of the most practical leaky-wave and resonant CRLH antennas, which all exhibit functionalities or/and performance superior to prior state of the art.
Abstract: Composite right-/left-handed (CRLH) transmission-line (TL) metamaterials, with their rich dispersion and fundamental right-/left-hand duality, represent a paradigm shift in electromagnetics engineering and, in particular, for antennas. This paper presents an overview of the most practical leaky-wave and resonant CRLH antennas, which all exhibit functionalities or/and performance superior to prior state of the art. The leaky-wave antennas provide full-space dynamic scanning capability, with fan beams, conical beams in uni-planar configurations, pencil beams without any complex feeding network, and actively shaped beams based on the concept of aperture digitization. The resonant antennas offer alternative properties and a solution to beam-squinting when no scanning is required, including multi-band (dual/tri-band) operation, zeroth-order high efficiency, high directivity, and planar electric and magnetic monopole radiators.
TL;DR: This work describes the first practical realization of a cylindrical cloak for linear surface liquid waves and demonstrates theoretically its unique mechanism using homogenization theory: the cloak behaves as an effective anisotropic fluid characterized by a diagonal stress tensor in acylindrical basis.
Abstract: We describe the first practical realization of a cylindrical cloak for linear surface liquid waves. This structured metamaterial bends surface waves radiated by a closely located acoustic source over a finite interval of Hertz frequencies. We demonstrate theoretically its unique mechanism using homogenization theory: the cloak behaves as an effective anisotropic fluid characterized by a diagonal stress tensor in a cylindrical basis. A low azimuthal viscosity is achieved, where the fluid flows most rapidly. Numerical simulations demonstrate that the homogenized cloak behaves like the actual structured cloak. We experimentally analyze the decreased backscattering of a fluid with low viscosity and finite density (methoxynonafluorobutane) from a cylindrical rigid obstacle surrounded by the cloak when it is located a couple of wavelengths away from the acoustic source.
04 May 2008
TL;DR: In this article, planar magnetic photonic metamaterials were fabricated via direct laser writing and silver chemical vapor deposition, an approach which is also suitable for three-dimensional structures, revealing the importance of bi-anisotropy.
Abstract: We fabricate planar magnetic photonic metamaterials via direct laser writing and silver chemical vapor deposition, an approach, which is also suitable for three-dimensional structures. Retrieval of the effective metamaterial parameters reveals the importance of bi-anisotropy.
Posted Content•
TL;DR: In this paper, the relationship between optics and general relativity is discussed, expressed more precisely between geometrical ideas normally applied in general relativity and the propagation of light, or electromagnetic waves in general, in materials.
Abstract: Metamaterials are beginning to transform optics and microwave technology thanks to their versatile properties that, in many cases, can be tailored according to practical needs and desires. Although metamaterials are surely not the answer to all engineering problems, they have inspired a series of significant technological developments and also some imaginative research, because they invite researchers and inventors to dream. Imagine there were no practical limits on the electromagnetic properties of materials. What is possible? And what is not? If there are no practical limits, what are the fundamental limits? Such questions inspire taking a fresh look at the foundations of optics and at connections between optics and other areas of physics. In this article we discuss such a connection, the relationship between optics and general relativity, or, expressed more precisely, between geometrical ideas normally applied in general relativity and the propagation of light, or electromagnetic waves in general, in materials. We also discuss how this connection is applied: in invisibility devices, perfect lenses, the optical Aharonov-Bohm effect of vortices and in analogues of the event horizon.
TL;DR: In this paper, a hybrid-metamaterial architecture is proposed for tuning a far-infrared resonance frequency with vanadium dioxide (VO2), a material whose optical properties can be strongly and quickly changed via external stimulus.
Abstract: We demonstrate a metamaterial device whose far-infrared resonance frequency can be dynamically tuned. Dynamic tuning should alleviate many bandwidth-related roadblocks to metamaterial application by granting a wide matrix of selectable electromagnetic properties. This tuning effect is achieved via a hybrid-metamaterial architecture; intertwining split ring resonator metamaterial elements with vanadium dioxide (VO2)-a material whose optical properties can be strongly and quickly changed via external stimulus. This hybrid structure concept opens a fresh dimension in both exploring and exploiting the intriguing electromagnetic behavior of metamaterials.
TL;DR: The recent developments on large-scale, multiple-functional-layer metamaterials are discussed in detail, and alternative methods for 3D fabrication of complex structures are mentioned.
TL;DR: The size effect in the imaginary part of the dielectric function is significant for both polarizations of light, parallel and perpendicular to the strips with relatively large A-parameter.
Abstract: Ag permittivity (dielectric function) in coupled strips is different from bulk and has been studied for strips of various dimensions and surface roughness. Arrays of such paired strips exhibit the properties of metamagnetics. The surface roughness does not affect the Ag dielectric function, although it does increase the loss at the plasmon resonances of the coupled strips. The size effect in the imaginary part of the dielectric function is significant for both polarizations of light, parallel and perpendicular to the strips with relatively large A-parameter.
TL;DR: Experiments on second- and third-harmonic generation from magnetic metamaterials composed of nanoscale gold split-ring resonators and from control samples for excitation with 170-fs pulses centered at 1.5-microm wavelength show the strongest nonlinear signals are found for resonances with magnetic-dipole character.
Abstract: Photonic metamaterials could provide optical nonlinearities far exceeding those of natural substances due to the combined action of (magnetic) resonances and local-field enhancements. Here, we present our experiments on second- and third-harmonic generation from magnetic metamaterials composed of nanoscale gold split-ring resonators and from control samples for excitation with 170-fs pulses centered at 1.5-μm wavelength. The strongest nonlinear signals are found for resonances with magnetic-dipole character.
TL;DR: In this paper, the authors demonstrate optical activity in an intrinsically non-chiral anisotropic planar metamaterial, which is due to extrinsic chirality resulting from the mutual orientation of the metammaterial structure and the incident electromagnetic wave.
Abstract: We demonstrate optical activity in an intrinsically non-chiral anisotropic planar metamaterial. The phenomenon is due to extrinsic chirality resulting from the mutual orientation of the metamaterial structure and the incident electromagnetic wave. The polarization effect, which has a resonant nature, features a spectral band where linear birefringence is practically absent and can be easily tuned by tilting the plane of the metamaterial relative to the incident beam.
TL;DR: A novel design which can enhance the electromagnetic wave scattering cross section of an object so that it looks like a scatterer bigger than the scale of the device is proposed.
Abstract: Based on the concept of complementary media, we propose a novel design which can enhance the electromagnetic wave scattering cross section of an object so that it looks like a scatterer bigger than the scale of the device. Such a "superscatterer" is realized by coating a negative refractive material shell on a perfect electrical conductor cylinder. The scattering field is analytically obtained by Mie scattering theory, and confirmed by full-wave simulations numerically. Such a device can be regarded as a cylindrical concave mirror for all angles.
TL;DR: In this paper, different routes for the generation of nanoporous metallic foams and films exhibiting well-defined pore size and short-range order are reviewed, and the authors suggest more in-depth investigations of the plasmonic and photonic properties of this material system for photonic applications.
Abstract: We review different routes for the generation of nanoporous metallic foams and films exhibiting well-defined pore size and short-range order. Dealloying and templating allows the generation of both 2D and 3D structures that promise a plasmonic response determined by material constituents and porosity. Viewed in the context of metamaterials, the ease of fabrication of samples covering macroscopic dimensions is highly promising, and suggests more in-depth investigations of the plasmonic and photonic properties of this material system for photonic applications.