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Negative index metamaterial or negative index material (NIM) is a metamaterial where the refractive index for an electromagnetic wave can be determined and has a negative value over some frequency range.〔 NIMs are constructed of periodic basic parts called unit cells, which are usually significantly smaller than the wavelength. The unit cells of the first experimentally investigated NIMs were constructed from circuit board material, or in other words, wires and dielectrics. And in general, these artificially constructed cells are stacked or planar and configured in a particular repeated pattern to compose the individual NIM material. For instance, the unit cells of the first NIMs were stacked horizontally and vertically, resulting in a pattern that was repeated and intended (see below images). Specifications for the response of each unit cell are predetermined prior to construction and are based on the intended or desired response of the entire, newly constructed, material. In other words, each cell is individually tuned to respond in a certain way, based on the desired output of the NIM. The aggregate response is mainly determined by the ''geometry'' unit cell, and substantially differs from the response of its constituent materials. In other words, the way the NIM responds is that of a new material, unlike the wires and dielectrics it is made from. Hence, the NIM has become an effective medium. Also, in effect, this metamaterial has become an “ordered macroscopic material, synthesized from the bottom up”, and has emergent properties beyond its components.〔Shivola, Ari. "(Electromagnetic Emergence in Metamaterials: Deconstruction of terminology of complex media )". ''Advances in Electromagnetics of Complex Media and Metamaterials''. Eds. Saïd Zouhdi, Ari Sihvola, Mohamed Arsalane. pgs. 3-18 Kluewer Academic. 2002.〕 Metamaterials which exhibit a negative value for the refractive index such as negative index materials are often referred to by any of several terminologies: left-handed media or left-handed material (LHM), backward wave media (BW media), media with negative refractive index, double negative (DNG) metamaterials, and other similar names.〔In the literature, most widely used designations are "double negative" and "left-handed". 〕 ==Properties and characteristics== Electrodynamics of media with negative index of refraction were first studied by a Russian theorist Victor Veselago in 1967.〔 The proposed ''left-handed'' or ''negative index'' materials were theorized to exhibit optical properties opposite to those of glass, air, and other transparent media. Such materials were predicted to exhibit counterintuitive properties like bending or refracting light in unusual and unexpected ways. However, the first practical metamaterial was not constructed until 33 years later and it does produce Veselago's concepts.〔〔〔 〕〔 Currently, negative index metamaterials are being developed to manipulate electromagnetic radiation in new ways. For example, optical and electromagnetic properties of natural materials are often altered through chemistry. With metamaterials, optical and electromagnetic properties can be engineered by changing the geometry of its unit cells. The unit cells are materials that are ordered in geometric arrangements with dimensions that are fractions of the wavelength of the radiated electromagnetic wave. Each artificial unit responds to the radiation from the source. The collective result is the material's response to the electromagnetic wave that is broader than normal.〔〔〔 Subsequently, transmission is altered by adjusting the shape, size, and configurations of the unit cells. This results in control over material parameters known as permittivity and magnetic permeability. These two parameters (or quantities) determine the propagation of electromagnetic waves in matter. Therefore, controlling the values of permittivity and permeability means that the refractive index can be negative or zero as well as conventionally positive. It all depends on the intended application or desired result. So, optical properties can be expanded beyond the capabilities of lenses, mirrors, and other conventional materials. Additionally, one of the effects most studied is the negative index of refraction.〔〔〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Negative index metamaterials」の詳細全文を読む スポンサード リンク
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