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METAMATERIALS<br />Introduction to METAMATERIALS and APPLICATION<br />

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Refractive Index <br />The refractive index, n, of a medium is defined as the ratio of the speed, C, of a wave phenomenon such as light or sound in a reference medium to the phase speed, Vp, of the wave in the medium.<br /> n = C / Vp <br />

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Refractive index below 1<br />A widespread misconception is that since, according to the theory of relativity, nothing can travel faster than the speed of light in vacuum, the refractive index cannot be lower than 1. This is erroneous since the refractive index measures the phase velocity of light, which does not carry energy or information, which are the two things limited in propagation speed. The phase velocity is the speed at which the crests of the wave move and can be faster than the speed of light in vacuum, and thereby give a refractive index below 1.<br />

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Phase Velocity<br />The phase velocity of a wave is the rate at which the phase of the wave propagates in space. This is the speed at which the phase of any one frequency component of the wave travels.<br />Phase velocity can exceed C because it does not carry any energy or information.<br />

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Metamaterials<br />Metamaterials usually gain their properties from structure rather than composition.<br />Depending on the structure , metamaterials may have refractive index less than 1 and even negative.<br />Size of structural components of metamaterials is restricted in range of wavelength of operation .<br />

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Left Handed Materials (LHMs)<br />Left-handed media (LHM), Backward wave media (BW media).<br />LHM have negative value of refractive index.<br />Victor Veselago , a Russian physicist first showed in his research that if a material has negative value of both permittivity, ε, and permeability μ simultaneously will have negative value of refractive index.<br />

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Limitation of natural materials<br />Most dielectrics only have positive permittivities , ε > 0 . <br />Metals will exhibit negative permittivity, ε < 0 at optical frequencies, and plasmas exhibit negative permittivity values in certain frequency bands. <br />However, in each of these cases permeability remains always positive.<br /> At microwave frequencies, it is possible for negative μ to occur in some ferromagnetic materials. But, the inherent drawback is they are difficult to find above terahertz frequencies.<br /> In any case, a natural material that can achieve negative values for permittivity and permeability simultaneously has not been found, or discovered.<br />

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Composite Materials<br />These are synthetic materials constructed to have physical properties never before produced in nature.<br />Synthetic materials could be constructed to purposely exhibit an negative permittivity and permeability simultaneously .<br />Size of resonators and copper wire used in these materials are almost equal to wavelength of operation.<br />

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Left Handed Materials (LHMs)<br />

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Application of Metamaterials <br />Metamaterial antenna<br />Superlens<br />Cloaking device<br />Invisible Submarines<br />Photonics OR opto-electronics<br />Create the oft-discussed, Invisible Man<br />Perfect Absorber of light<br />Ultra high capacity storage devices etc.<br />

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Metamaterial antenna<br />

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Metamaterial antenna<br />The challenge of the antenna field is that there are fundamental limitations on antenna quality factor and its electrical size.<br />These antennas measure just a few millimetres long and are as flat as paper, the new multiband antennas could double the range, reliability and battery life of cellular phones, Wi-Fi routers and wireless modems.<br />The newest metamaterials antennas radiate as much as 95 percent of an input radio signal.<br />Conventional antennas that are very small compared to the wavelength, most of the signal is reflected back to the source. <br />The metamaterial , on the other hand, makes the antenna behave as if it were much larger than it really is, because the novel antenna structure stores energy, and re-radiates it.<br />Because of small size these antennas can be used on limited space platforms as on-board airplanes and ships . <br />

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Diffraction-limit<br />The resolution of an optical imaging system ,a microscope, telescope, or camera can be limited by factors such as imperfections in the lenses or misalignment.<br />The minimum angular separation of two sources that can be distinguished by a telescope depends on the wavelength of the light being observed and the diameter of the telescope. This angle is called the DIFFRACTION LIMIT.<br />

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Beyond diffraction limit (superlens)<br />A superlens , super lens or perfect lens is a lens which uses metamaterials to go beyond the diffraction limit.<br />Lenses that have no blurring effect, resulting in ultra-sharp images.<br />Both propagating and evanescent waves contribute to the resolution of the image<br />But wavelength of operation is limited by size of components used in metamaterial so this is still not possible to use visible light (wave length in nanometres) but it was successful in microwave range.<br />

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Cloaking device<br />The Duke cloaking device only masks an object from one wavelength of microwave light.<br />

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Cloaking device<br />it is possible to design metamaterial "cloak" so that it guides light around some region, rendering it invisible over a certain band of wavelengths.<br />The Duke team used metamaterials to make their cloaking device have gradually varying refractive indices - from 1 on the outside of the device, decreasing to zero in the centre . The result is that microwave light subtly bends around the device and is able to reform on the other side, although with some detectable distortion .<br />

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Cloaking device (limitations)<br />Due to limitation on size ,still its not possible to make a cloak device for operating wavelength in visible band.<br />Current devices work only for one wavelength but visible light has many wavelength .<br />People inside a cloaked area wouldn't be able to see out because all visible light would be bending around where they are positioned. They'd be invisible, but they'd be blind, too.<br />

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Cloaking device( possibilities ) <br />Making a large building invisible so that the park on the other side can be seen.<br />Improving the range of wireless devices by allowing waves to bend and flow around obstructing objects.<br />Cloaked military vehicles and outposts .<br />Eliminating shadows and reflections (from a military plane, for example)<br />Etc.<br />

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Figure out the big bang<br />Using metamaterials, scientists can create a “toy big bang” using precisely designed metamaterials that are mathematically analogous to certain conditions of the real-world big bang<br />