Metamaterial 906878 221206810 2008-06-23T14:41:15Z Thijs!bot 1392310 robot Adding: [[nl:Metamateriaal]] A '''metamaterial''' (or '''meta material''') is a material which gains its properties from its structure rather than directly from its composition. To distinguish metamaterials from other [[composites|composite]] materials, the ''metamaterial'' label is usually used for a material which has unusual properties. The term was coined in 1999 by Rodger M. Walser of the [[University of Texas at Austin]]. He defined metamaterials as:<ref>R.M. Walser, in: W.S. Weiglhofer and A. Lakhtakia (Eds.), [http://spie.org/x648.xml?product_id=504610 Introduction to Complex Mediums for Electromagnetics and Optics], SPIE Press, Bellingham, WA, USA, 2003</ref> <blockquote> Macroscopic composites having a manmade, three-dimensional, periodic cellular architecture designed to produce an optimized combination, not available in nature, of ''two or more responses'' to specific excitation. </blockquote> Among electromagnetics researchers, the term is often used, quite narrowly, for materials which exhibit negative refraction. The first metamaterials were developed by W.E. Kock in the late 1940s with metal-lens antennas<ref>IRE Proc., 34 November 1946, pp. 828-836</ref> and metallic delay lenses<ref>Bell. Sys. Tech. Jour., 27, January 1948, pp. 58-82</ref>. == Electromagnetic metamaterials == Metamaterials are of particular importance in [[electromagnetism]] (especially [[optics]] and [[photonics]]). They show promise for a variety of optical and [[microwave]] applications such as new types of [[beam steerer]]s, [[modulator]]s, [[band-pass filter]]s, [[superlens|lenses]], [[microwave coupler]]s, and [[antenna radome]]s. In order for its structure to affect [[electromagnetic wave]]s, a metamaterial must have structural features smaller than the [[wavelength]] of the [[electromagnetic radiation]] it interacts with. For instance, if a metamaterial is to behave as a homogeneous material accurately described by an effective [[refractive index]], the feature sizes must be much smaller than the wavelength. For [[visible light]], which has wavelengths of less than one [[micrometre]] typically (560 [[nanometers]] for sunlight), the structures are generally half or less than half this size; i.e., less than 280 nanometres. For [[microwave]] radiation, the structures need only be on the order of one [[decimetre]]. [[Microwave]] frequency metamaterials are almost always artificial, constructed as arrays of current-conducting elements (such as loops of wire) which have suitable [[inductor|inductive]] and [[capacitor|capacitive]] characteristics. Metamaterials usually consist of periodic structures, and thus have many similarities with [[photonic crystals]] and [[frequency selective surfaces]]. However, these are usually considered to be distinct from metamaterials, as their features are of similar size to the wavelength at which they function, and thus cannot be approximated as a homogeneous material. ==Negative refractive index== [[Image:metarefraction.svg|thumb|A comparison of refraction in a left-handed metamaterial to that in a normal material]] The main reason researchers have investigated metamaterials is the possibility to create a structure with a negative [[refractive index]], since this property is not found in any naturally occurring material. Almost all materials encountered in optics, such as glass or [[water]], have positive values for both [[permittivity]] <math>\epsilon</math> and [[permeability (electromagnetism)|permeability]] <math>\mu</math>. However, many metals (such as [[silver]] and [[gold]]) have negative <math>\epsilon</math> at visible wavelengths. A material having either (but not both) <math>\epsilon</math> or <math>\mu</math> negative is [[opacity (optics)|opaque]] to electromagnetic radiation (see [[surface plasmon]] for more details). Although the optical properties of a transparent material are fully specified by the parameters <math>\epsilon</math> and <math>\mu</math>, in practice the [[refractive index]] <math>N</math> is often used. <math>N</math> may be determined from <math>N=\pm\sqrt{\epsilon\mu}</math>. All known transparent materials possess positive values for <math>\epsilon</math> and <math>\mu</math>. By convention the positive square root is used for <math>N</math>. However, some engineered metamaterials have <math>\epsilon<0</math> and <math>\mu<0</math>; because the product <math>\epsilon\mu</math> is positive, <math>N</math> is [[real number|real]]. Under such circumstances, it is necessary to take the negative square root for <math>N</math>. Physicist [[Victor Veselago]] proved that such substances can [[transparency (optics)|transmit light]]. The foregoing considerations are simplistic for actual materials, which must have complex-valued <math>\epsilon</math> and <math>\mu</math>. The real parts of both <math>\epsilon</math> and <math>\mu</math> do not have to be negative for a passive material to display negative refraction.<ref> R.A. Depine and A. Lakhtakia, [http://dx.doi.org/10.1002/mop.20127 A new condition to identify isotropic dielectric-magnetic materials displaying negative phase velocity], Microwave and Optical Technology Letters, Vol. 41, pp. 315-316, 2004</ref> Metamaterials with negative <math>N</math> have numerous startling properties: *[[Snell's law]] (<math> N_1\sin\theta_1=N_2\sin\theta_2</math>) still applies, but as <math>N_2</math> is negative, the rays will be refracted on the ''same'' side of the normal on entering the material. *The [[Doppler shift]] is reversed: that is, a light source moving toward an observer appears to reduce its frequency. *[[Cherenkov radiation]] points the other way. *The time-averaged Poynting vector is [[antiparallel (mathematics)|antiparallel]] to [[phase velocity]]. This means that unlike a normal right-handed material, the wave fronts are moving in the opposite direction to the flow of energy. For [[plane wave]]s propagating in such metamaterials, the [[electric field]], [[magnetic field]] and [[wave vector]] follow a [[left-handed material|left-hand rule]], thus giving rise to the name left-handed (meta)materials. It should be noted that the terms left-handed and right-handed can also arise in the study of [[chiral]] media, but their use in that context is unrelated to this effect. Some researchers consider the qualifier left-handed for achiral materials as particularly infelicitous. The effect of negative refraction is analogous to wave propagation in a left-handed [[transmission line]], and such structures have been used to verify some of the effects described here. ==Development and applications== The first metamaterials were developed by W.E. Kock in the late 1940's<ref>Metal-lens antennas, IRE Proc., 34 November 1946, pp. 828-836 and Metallic delay lenses, Bell. Sys. Tech. Jour.,27, January 1948, pp. 58-82</ref>. The unique properties of metamaterials were verified by full-wave analysis in Caloz ''et al.'' (2001).<ref>C. Caloz, C.-C. Chang, and T. Itoh, "Full-wave verification of the fundamental properties of left-handed materials in waveguide configurations," J. Appl. Phys. 2001, 90(11)</ref>. However, the LH structures devised up to 2002 were impractical for microwave applications, because they had a too narrow bandwidth and were quite lossy. Eleftheriades ''et al.'' (2002), and Caloz ''et al.'' (2002) provided a method to realize left-handed metamaterials using artificial lumped-element loaded transmission lines in microstrip technology.<ref>G.V. Eleftheriades, A.K. Iyer and P.C. Kremer, "Planar negative refractive index media using periodically L-C loaded transmission lines," IEEE Trans. on Microwave Theory and Techniques, vol. 50, no. 12, pp. 2702-2712, 2002</ref><ref>C. Caloz and T. Itoh, "Application of the transmission line theory of left-handed (LH) materials to the realization of a microstrip 'LH line'," IEEE Antennas and Propagation Society International Symposium, 2002, 2, 412-415 (doi 10.1109/APS.2002.1016111).</ref> The first [[superlens]] with a negative refractive index provided resolution three times better than the [[diffraction limit]] and was demonstrated at microwave frequencies at the [[University of Toronto]] by A. Grbic and G.V. Eleftheriades<ref>A. Grbic and G.V. Eleftheriades, "Overcoming the diffraction limit with a planar left-handed transmission-line lens," Physical Review Letters, vol. 92, no. 11, pp. 117403 , March 19, 2004</ref>. Subsequently, the first optical superlens (an optical lens which exceeds the [[diffraction limit]]) was created and demonstrated in 2005 by Xiang Zhang ''et al.'' of UC Berkeley, as reported that year in the April 22 issue of the journal Science.<ref>[http://www.eurekalert.org/pub_releases/2005-04/uoc--nso041805.php New superlens opens door to nanoscale optical imaging, high-density optoelectronics<!-- Bot generated title -->]</ref> But their lens didn't rely on negative refraction. Instead, they used a thin silver film to enhance the evanescent modes through [[surface plasmon]] coupling. This idea was first suggested by [[John Pendry]] in ''[[Physical Review Letters]]''. Metamaterials have been proposed as a mechanism for building a [[cloaking device]]. These mechanisms typically involve surrounding the object to be cloaked with a shell which affects the passage of light near it.<ref>http://cnn.com/2006/TECH/05/25/invisibility.cloak.ap/index.html</ref> [[Duke University]] and [[Imperial College London]] are currently researching this use of metamaterials and have managed to use metamaterials to cloak an object (in the microwave spectrum) using special concentric rings; the microwaves were barely affected by the presence of the cloaked object.<ref>[http://www.pratt.duke.edu/news/releases/index.php?story=276 News Releases, Feature Stories and Profiles about Duke University's Pratt School of Engineering<!-- Bot generated title -->]</ref> In early 2007, a metamaterial with a negative index of refraction for visible light wavelengths was announced by a joint team of researchers at the [[Ames Laboratory]] of the [[United States Department of Energy]] and at [[Karlsruhe University]] in [[Germany]]. The material had an index of -0.6 at 780 nanometers.<ref>[http://www.eurekalert.org/pub_releases/2007-01/dl-mft010407.php?light Metamaterials found to work for visible light<!-- Bot generated title -->]</ref> Metamaterials have been also proposed for designing agile antennas.<ref>http://membres.lycos.fr/hocine/TAPCEBG.pdf</ref> ==Theoretical models== Left-handed (LH) materials were first introduced theoretically by [[Victor Veselago]] in 1967<ref>{{cite journal|author=Veselago VG|title=The electrodynamics of substances with simultaneously negative values of ε and μ|journal=Sov. Phys. Usp.|volume=10|issue=4|pages=509–14|year=1968|doi=10.1070/PU1968v010n04ABEH003699|url=http://ufn.ru/en/articles/1968/4/a/}}</ref><ref>{{cite journal|author=Veselago VG|title=The electrodynamics of substances with simultaneously negative values of ε and μ|journal=Usp. Fiz. Nauk|volume=92|pages=517–526|year=1967| language = Russian|url=http://ufn.ru/ru/articles/1967/7/j/ }}</ref>. [[John Pendry|J. B. Pendry]] was the first to theorize a practical way to make a left-handed metamaterial (LHM). 'Left-handed' in this context means a material in which the '[[right-hand rule]]' is not obeyed, allowing an electromagnetic wave to convey energy (have a [[group velocity]]) in the opposite direction to its [[phase velocity]]. Pendry's initial idea was that metallic wires aligned along propagation direction could provide a metamaterial with negative permittivity (ε<0). Note however that natural materials (such as [[Ferroelectricity|ferroelectrics]]) were already known to exist with negative permittivity: the challenge was to construct a material which also showed negative permeability (µ<0). In 1999, Pendry demonstrated that an open ring ('C' shape) with axis along the propagation direction could provide a negative permeability. In the same paper, he showed that a periodic array of wires and ring could give rise to a negative refractive index. A related negative permeability particle which was also proposed by Professor Pendry is the [[Swiss roll (metamaterial)|Swiss roll]]. The analogy is as follows: Natural materials are made of atoms, which are dipoles. These dipoles modify the light velocity by a factor n (the refractive index). The ring and wire units play the role of atomic dipoles: the wire acts as a ferroelectric atom, while the ring acts as an inductor L and the open section as a capacitor C. The ring as a whole therefore acts as a LC circuit. When the electromagnetic field passes through the ring, an induced current is created and the generated field is perpendicular to the magnetic field of the light. The magnetic resonance results in a negative permeability; the index is negative as well. (The lens is not truly flat as the C and its nearby Cs imposes a slope for the electric induction.) ==See also== *[[List of emerging technologies]] * [[Transformation optics]] ==References== <references/> ==External links== ===Research groups (''in alphabetical order'')=== #[http://www.imr.salford.ac.uk/people/academic%20staff/allan%20boardman.shtml Allan Boardman's Group - UK] #[http://www.calozgroup.org Christophe Caloz' research group — Canada] #[http://www.waves.utoronto.ca/prof/gelefth/main.html George Eleftheriades's research group — Canada] #[http://www.seas.upenn.edu/~engheta/ Nader Engheta - US] #[http://www.fhr.fgan.de/fhr/fhr_c648_f4_en.html FGAN-FHR — Germany] #[http://www.ece.ucdavis.edu/inano/ M. Saif Islam's Research Group, University of California at Davis - USA] #[http://www.mwlab.ee.ucla.edu Tatsuo Itoh`s group — USA] #[http://www.esm.psu.edu/~axl4/lakhtakia/ALNPV.html Akhlesh Lakhtakia - USA] #[http://www.elec.qmul.ac.uk/antennas Antennas & Electromagnetics Group, Queen Mary, University of London - UK] #[http://ssls.nus.edu.sg/ Herbert Moser's Group, Singapore Synchrotron Light Source — Singapore] #[http://www.fen.bilkent.edu.tr/~ozbay/ Ekmel Özbay`s Research group, Bilkent University - Turkey] #[http://www.cmth.ph.ic.ac.uk/photonics/references.html Sir John Pendry's group — References — Imperial College — UK] #[http://www2.bc.edu/~padillaw/ Willie Padilla's research group — Boston College — USA] #[http://www.physics.oregonstate.edu/~vpodolsk Viktor Podolskiy's group — Oregon State University — USA] #[http://cobweb.ecn.purdue.edu/~photspec/index.shtml Vladimir Shalaev's Research Group, Purdue University, USA] #[http://www.ph.utexas.edu/~shvetsgr/lens.html Shvets Research Group, University of Texas at Austin - USA] #[http://www.ee.duke.edu/~drsmith/ David Smith's research group — Duke University — USA ] #[http://esperia.iesl.forth.gr/~ppm/Research.html Costas Soukoulis at IESL, Greece — Photonic, Phononic & MetaMaterials Group] #[http://sagar.physics.neu.edu/ Srinivas Sridhar's Group, Northeastern University — USA] #[http://metamorphose-VI.org Virtual Institute for Artificial Electromagnetic Materials and Metamaterials ("METAMORPHOSE VI AISBL")] #[http://metamorphose-EU.org "Metamorphose" EU Network of Excellence on Metamaterials. Coordinator: Sergei Tretyakov] #[http://tona.vub.ac.be Irina Veretennicoff's research group, Vrije Universiteit Brussel — Belgium] #[http://www.aph.uni-karlsruhe.de/wegener/en/research/metamaterials Martin Wegener's Metamaterials group, Universität Karlsruhe (TH) — Germany] #[http://metamaterialsPLUS.com Georgios Zouganelis's Metamaterials Group, NIT — Japan] #[http://xlab.me.berkeley.edu Xiang Zhang's group, Berkeley USA] #[http://www.dea.uniroma3.it/lema/ Applied Electromagnetics Laboratory, Lucio Vegni's group, Università "Roma Tre", Rome] #[http://naps.riken.go.jp/tanaka/ Takuo Tanaka and Satoshi Kawata, Nanophotonics Lab., RIKEN (The Institute of Physical and Chemical Research), Japan] #[http://www.lgep.supelec.fr/mocosem/perso/zouhdi/ Said Zouhdi's group, LGEP at SUPELEC, France] #[http://users.tkk.fi/~sergei/ Sergei Tretyakov's group, Helsinki University of Technology, Finland] #[http://cimitec.uab.es/ CIMITEC, Universitat Autònoma de Barcelona, Spain] #[http://newton.ex.ac.uk/research/emag/ Sambles and Barnes Research Group, University of Exeter - UK] ===Internet portals=== #[http://www.elsevier.com/locate/metmat/ Journal "Metamaterials" published by Elsevier (homepage)] #[http://www.sciencedirect.com/science/journal/18731988 Online articles: "Metamaterials" in ScienceDirect] #[http://feeds.aps.org/rss/topics/metamaterials.xml RSS feed for Metamaterials articles published in Physical Review Journals] #[http://metamaterials.net MetaMaterials.net Web Group] #[http://metamorphose-VI.org Virtual Institute for Artificial Electromagnetic Materials and Metamaterials ("METAMORPHOSE VI AISBL")] #[http://metamorphose-EU.org European Network of Excellence "METAMORPHOSE" on Metamaterials] ===More articles and presentations (''newest is first'')=== #[http://www.flintbox.com/technology.asp?page=3142 UWB Tunable Delay System, Prof Christophe Caloz, Ecole Polytechnique de Montreal)] #[http://www.metaphotonics.de Metaphotonics.de - Information about Photonic Metamaterials in Karlsruhe (HHNG Dr. Stefan Linden and Prof. Dr. Martin Wegener)] #[http://www.imagico.de/pov/metamaterials.html Realistic raytraced images, videos and interactive web-based demonstrations of materials with negative index of refraction.] #[http://metamaterialsPLUS.com Cloaking devices, nihility bandgap, LF magnetic enhancement, perfect radome] NIT Japan #[http://emtalk.com/tut_4.htm Left-Handed Flat Lens HFSS Tutorial] EM Talk Tutorial #[http://iop.org/EJ/toc/1464-4258/7/2 Journal of Optics A, February 2005] Special issue on Metamaterials #[http://physics.ucsd.edu/lhmedia Experimental Verification of a Negative Index of Refraction] #[http://physicsweb.org/articles/news/10/5/16/1 How To Make an Object Invisible] #[http://theuniversalseduction.com/articles/ee-times-metamaterials-hold-key-to-cloak-of-invisibility Metamaterials hold key to cloak of invisibility] [[Category:Materials science]] [[Category:Optics]] [[Category:Nanomaterials]] [[de:Metamaterial]] [[es:Metamateriales]] [[eo:Metamaterialo]] [[fr:Métamatériau]] [[it:Metamateriale]] [[nl:Metamateriaal]] [[ja:メタマテリアル]] [[pl:Metamateriał]] [[ru:Метаматериал]]