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MetamaterialIn electromagnetism (covering areas like optics and photonics), a meta material (or metamaterial) is an object that gains its (electromagnetic) material properties from its structure rather than inheriting them directly from the materials it is composed of. This term is particularly used when the resulting properties have not been found for naturally formed substances. Metamaterials are often made up of a collection of objects whose separation is much less than the wavelength of light passing through it. Using a wider definition, the most common example of metamaterial would be an optical medium such as glass; here the objects would be the individual atoms or molecules making up the substance. However, it is possible to construct arrays of current-conducting elements (such as loops of wire) that have a magnetic response at microwave frequencies. When electromagnetic radiation passes the wire loops, the magnetic field could induce an electric current, thus producing magnetic response. Negative refractive index Very nearly all materials encountered in optics, such as glass or water, have positive values for both permittivity and permeability . However, many metals (such as silver and gold) have negative at visible wavelengths. A material having either (but not both) or negative is opaque to electromagnetic radiation (see surface plasmon for more details). Although the optical properties of a transparent material are fully specified by the parameters and , in practice the refractive index is often used. may be determined from . All known transparent materials possess a positive index because and are both positive. However, some engineered metamaterials have and ; because the product is positive, is real. Under such circumstances, it is necessary to take the negative square root for . Physicist Victor Veselago proved that such substances are transparent to light. Metamaterials with negative have numerous startling properties: One common metamaterial is the Swiss roll. Such metamaterials follow a "left-hand rule". = External Links = * Experimental Verification of a Negative Index of Refraction
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