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Metamaterial cloaking is the usage of metamaterials in an invisibility cloak. This is accomplished by manipulating the paths traversed by light through a novel optical material. Metamaterials direct and control the propagation and transmission of specified parts of the light spectrum and demonstrate the potential to render an object seemingly invisible. Metamaterial cloaking, based on transformation optics, describes the process of shielding something from view by controlling electromagnetic radiation. Objects in the defined location are still present, but incident waves are guided around them without being affected by the object itself.〔〔〔〔 〕〔 ==Electromagnetic metamaterials== ''Electromagnetic metamaterials'' respond to chosen parts of radiated light, also known as the electromagnetic spectrum, in a manner that is difficult or impossible to achieve with natural materials. In other words, these metamaterials can be further defined as artificially structured composite materials, which exhibit interaction with light usually not available in nature (electromagnetic interactions). At the same time, metamaterials have the potential to be engineered and constructed with desirable properties that fit a specific need. That need will be determined by the particular application.〔〔〔 The artificial structure for cloaking applications is a lattice design – a sequentially repeating network – of identical elements. Additionally, for microwave frequencies, these materials are analogous to crystals for optics. Also, a metamaterial is composed of a sequence of elements and spacings, which are much smaller than the selected wavelength of light. The selected wavelength could be radio frequency, microwave, or other radiations, now just beginning to reach into the visible frequencies. Macroscopic properties can be directly controlled by adjusting characteristics of the rudimentary elements, and their arrangement on, or throughout the material. Moreover, these metamaterials are a basis for building very small cloaking devices in anticipation of larger devices, adaptable to a broad spectrum of radiated light.〔〔〔 Hence, although light consists of an electric field and a magnetic field, ordinary optical materials, such as optical microscope lenses, have a strong reaction only to the electric field. The corresponding magnetic interaction is essentially nil. This results in only the most common optical effects, such as ordinary refraction with common diffraction limitations in lenses and imaging.〔〔〔 Since the beginning of optical sciences, centuries ago, the ability to control the light with materials has been limited to these common optical effects. Metamaterials, on the other hand, are capable of a very strong interaction, or coupling, with the magnetic component of light. Therefore, the range of response to radiated light is expanded beyond the ordinary optical limitations that are described by the sciences of physical optics and optical physics. In addition, as artificially constructed materials, both the magnetic and electric components of the radiated light can be controlled at will, in any desired fashion as it travels, or more accurately propagates, through the material. This is because a metamaterial's behavior is typically formed from individual components, and each component responds independently to a radiated spectrum of light. At this time, however, metamaterials are limited. Cloaking across a broad spectrum of frequencies has not been achieved, including the visible spectrum. Dissipation, absorption, and dispersion are also current drawbacks, but this field is still in its optimistic infancy.〔〔〔 〕 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「Metamaterial cloaking」の詳細全文を読む スポンサード リンク
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