NationMaster - Encyclopedia: Metamaterial

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Encyclopedia > Metamaterial

A metamaterial (or meta material) is a material that gains its properties from its structure rather than directly from its composition. The first metamaterials were developed by W.E. Kock in the late 1940's with metal-lens antennas ^[1] and metallic delay lenses ^[2]. This term is most often used when the material has properties not found in naturally-formed substances. The term was coined by Rodger M. Walser of the University of Texas at Austin in 1999, and he defined the term as follows in 2002: 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. University of Texas redirects here. ...

Metamaterials are of particular importance in electromagnetism (especially optics and photonics), where they are promising for a variety of optical and microwave applications, such as new types of beam steerers, modulators, band-pass filters, lenses, microwave couplers, and antenna radomes. Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... For the book by Sir Isaac Newton, see Opticks. ... This article or section is in need of attention from an expert on the subject. ... Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) frequencies, but relatively short for radio waves. ... For the musical use of modulation, see modulation (music). ... The frequency axis of this symbolic diagram would be logarithmically scaled. ... A superlens is a lens which is capable of subwavelength imaging. ... Radomes at the Misawa Security Operations Center, Misawa, Japan. ...

In order for its structure to affect electromagnetic waves, a metamaterial must have structural features at least as small as the wavelength of the electromagnetic radiation it interacts with. In order for the metamaterial 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, this is on the order of one decimetre. An example of a visible light metamaterial is opal, which is composed of tiny cristobalite (metastable silica) spheres. Microwave frequency metamaterials are almost always artificial, constructed as arrays of current-conducting elements (such as loops of wire) that have suitable inductive and capacitive characteristics. Electromagnetic radiation is a propagating wave in space with electric and magnetic components. ... The wavelength is the distance between repeating units of a wave pattern. ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... A micrometre (American spelling: micrometer, symbol Âµm) is an SI unit of length equal to one millionth of a metre, or about a tenth of the diameter of a droplet of mist or fog. ... A nanometre (American spelling: nanometer) is 1. ... Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) frequencies, but relatively short for radio waves. ... A decimetre is a measurement of length, measuring 10 centimetres or one-tenth of a metre millimetre << centimetre << decimetre << metre << kilometre ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... For other OPAL articles, see Opal (disambiguation). ... Common in volcanic rocks, cristobalite is a high-temperature polymorph of quartz and tridymite. ... Metastability is the ability of a non-equilibrium state to persist for a long period of time. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) frequencies, but relatively short for radio waves. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ... See Capacitor (component) for a discussion of specific types. ...

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. The opal in this bracelet contains a natural periodic microstructure responsible for its iridescent color. ...

1 Negative refractive index
2 Development and applications
3 Theoretical models
4 References
5 External links

Negative refractive index

$A comparison of refraction in a left-handed metamaterial to that in a normal material$

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 $ε$ and permeability $μ$ . However, many metals (such as silver and gold) have negative $ε$ at visible wavelengths. A material having either (but not both) $ε$ or $μ$ negative is opaque to electromagnetic radiation (see surface plasmon for more details). Image File history File links Metarefraction. ... Image File history File links Metarefraction. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectric medium and is determined by the ability of a material to polarize in response to an applied electric field, and thereby to cancel, partially, the field inside the material. ... In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. ... General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Standard atomic weight 107. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... A substance or object that is opaque is neither transparent nor translucent. ... In physics, the plasmon is the particle resulting from the quantization of plasma oscillations, which are density waves of the charge carriers in a conducting medium such as a metal, semiconductor, or plasma. ...

Although the optical properties of a transparent material are fully specified by the parameters $ε$ and $μ$ , in practice the refractive index $N$ is often used. $N$ may be determined from $N=pmsqrt{epsilonmu}$ . All known transparent materials possess positive values for $ε$ and $μ$ . By convention the positive square root is used for $N$ . The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ...

However, some engineered metamaterials have $ε < 0$ and $μ < 0$ ; because the product $εμ$ is positive, $N$ is real. Under such circumstances, it is necessary to take the negative square root for $N$ . Physicist Victor Veselago proved that such substances can transmit light. In mathematics, the real numbers may be described informally as numbers that can be given by an infinite decimal representation, such as 2. ... Professor Veselago Victor G. Veselago (born 1929, in Ukrainian SSR, USSR) - Russian physicist who, in 1967, theoretically envisioned negative permittivity negative permeability materials. ... Transparent glass ball In optics, transparency is the property of allowing light to pass. ...

Metamaterials with negative $N$ have numerous startling properties:

Snell's law ( $N 1 sinθ 1 = N 2 sinθ 2$ ) still applies, but as $N 2$ 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 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 waves propagating in such metamaterials, the electric field, magnetic field and Poynting vector (or group velocity) follow a 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. Refraction of light at the interface between two media of different refractive indices, with n2 > n1. ... The Doppler effect is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves. ... Cherenkov radiation glowing in the core of a TRIGA reactor Cherenkov radiation (also spelled Cerenkov or sometimes ÄŒerenkov) is electromagnetic radiation emitted when a charged particle passes through an insulator at a speed greater than the speed of light in that medium. ... Two antiparallel molecules run side-by-side in opposite directions. ... The phase velocity of a wave is the rate at which the phase of the wave propagates in space. ... In the physics of wave propagation (especially electromagnetic waves), a plane wave (also spelled planewave) is a constant-frequency wave whose wavefronts (surfaces of constant amplitude and phase) are infinite parallel planes normal to the propagation direction. ... In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ... Magnetic field lines shown by iron filings In physics, a magnetic field is a solenoidal vector field in the space surrounding moving electric charges and magnetic dipoles, such as those in electric currents and magnets. ... The Poynting vector describes the energy flux (JÂ·mâˆ’2Â·sâˆ’1) of an electromagnetic field. ... The group velocity of a wave is the velocity with which the variations in the shape of the waves amplitude (known as the modulation or envelope of the wave) propagate through space. ... Left-handed materials are metamaterials which have a negative refractive index. ... Chirality refers to several phenomena, all having to do with objects that differ from their mirror image. ...

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. A transmission line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electromagnetic waves or acoustic waves, as well as electric power transmission. ...

Development and applications

The first metamaterials were developed by W.E. Kock in the late 1940's 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.

The unique properties of metamaterials were verified by full-wave analysis in Caloz et al. (2001). ^[3] 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.^[4]^[5]

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^[6]. Subsequently, the first optical superlens (an optical lens that 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.^[7] 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. A superlens is a lens which is capable of subwavelength imaging. ... Diffraction is the apparent bending and spreading of waves when they meet an obstruction. ... The University of Toronto (U of T) is a public research university in the city of Toronto, Ontario, Canada. ... Diffraction is the apparent bending and spreading of waves when they meet an obstruction. ... In physics, the plasmon is the particle resulting from the quantization of plasma oscillations, which are density waves of the charge carriers in a conducting medium such as a metal, semiconductor, or plasma. ... Professor Sir John Brian Pendry FRS BA MA PhD FInstP, (born 1944), is an English theoretical physicist. ... Physical Review Letters is one of the most prestigious journals in physics. ...

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 that affects the passage of light near it.^[8] Duke University and Imperial College London are currently researching this use of metamaterials and has 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.^[9] 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.^[10] A Klingon Bird of Prey from Star Trek VI: The Undiscovered Country fires while using a cloaking device In several science fiction universes, a cloaking device is an advanced stealth system which causes a spaceship or individual to be invisible and extremely difficult to detect with normal sensors. ... Duke University is a private coeducational research university located in Durham, North Carolina, USA. Founded by Methodists and Quakers in the present-day town of Trinity in 1838, the school moved to Durham in 1892. ... Imperial College London (also known as Imperial College of Science, Technology and Medicine) is a British university institution and a constituent college of the University of London. ... Ames Laboratory is a United States Department of Energy national laboratory located in Ames, Iowa. ... The United States Department of Energy (DOE) is a Cabinet-level department of the United States government responsible for energy policy and nuclear safety. ... The UniversitÃ¤t Karlsruhe (TH) is a mainly technical university in the city of Karlsruhe, Germany and is a leading research university. ...

Metamaterials have been also proposed for designing agile antennas ^[11].

Theoretical models

Left-handed (LH) materials were first introduced theoretically by Victor Veselago in 1967^[12]. Professor Veselago Victor G. Veselago (born 1929, in Ukrainian SSR, USSR) - Russian physicist who, in 1967, theoretically envisioned negative permittivity negative permeability materials. ...

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 ferroelectrics) were already known to exist with negative permittivity: the challenge was to construct a material that 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 that was also proposed by Professor Pendry is the Swiss roll. Professor Sir John Brian Pendry FRS BA MA PhD FInstP, (born 1944), is an English theoretical physicist. ... The left-handed orientation is shown on the left, and the right-handed on the right. ... The group velocity of a wave is the velocity with which the variations in the shape of the waves amplitude (known as the modulation or envelope of the wave) propagate through space. ... The phase velocity of a wave is the rate at which the phase of the wave propagates in space. ... This article or section is in need of attention from an expert on the subject. ... In optics, swiss roll is a kind of metamaterial that has negative refractive index. ...

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.)

References

^ IRE Proc., 34 November 1946, pp. 828-836
^ Bell. Sys. Tech. Jour.,27, January 1948, pp. 58-82
^ 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).
^ 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
^ 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).
^ 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
^ http://www.eurekalert.org/pub_releases/2005-04/uoc--nso041805.php
^ http://cnn.com/2006/TECH/05/25/invisibility.cloak.ap/index.html
^ http://www.pratt.duke.edu/news/releases/index.php?story=276
^ http://www.eurekalert.org/pub_releases/2007-01/dl-mft010407.php?light
^ http://membres.lycos.fr/hocine/TAPCEBG.pdf
^ Veselago VG (1968). "The electrodynamics of substances with simultaneously negative values of ε and μ". Sov. Phys. Usp. 10 (4): 509-14.

External links

Research groups (alphabetically)

Professor Allan Boardman is well-known both in the UK and globally for his work on surface plasmons and guided wave optics, especially nonlinear waves, solitons, magneto-optics and negative refracting metamaterials. ...

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