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Negative refraction is the name for an electromagnetic phenomenon where light rays are refracted at an interface in the reverse sense to that normally expected. Such an effect can be obtained using a metamaterial which has been designed to achieve a negative value for both (electric) permittivity ε and (magnetic) permeability μ, as in such cases the material can be assigned a negative refractive index. Such materials are sometimes called "double negative" materials. Negative refraction occurs at interfaces between materials at which one has an ordinary positive phase velocity (i.e. a positive refractive index), and the other has the more exotic negative phase velocity (a negative refractive index). ==Negative phase velocity== Negative phase velocity (NPV) is a property of light propagation in a medium. There are different definitions of NPV, the most common being Veselago's original proposal of opposition of wavevector and (Abraham) Poynting vector, i.e. E×H; other common choices are opposition of wavevector to group velocity, or to energy velocity. The use of "phase velocity" in the naming convention, as opposed to the perhaps more appropriate "wave vector", follows since phase velocity has the same sign as the wavevector. A typical criterion used to determine Veselago NPV is that the dot product of the Poynting vector and wavevector is negative (i.e. that ); however this definition is not covariant. Whilst this restriction is rarely of practical significance, the criterion has nevertheless been generalized into a covariant form. For plane waves propagating in a Veselago NPV medium, the electric field, magnetic field and wave vector follow a left-hand rule, rather than the usual right-hand rule. This gives rise to the name "left-handed (meta)materials". However, the terms left-handed and right-handed can also arise in the study of chiral media, so this terminology is best avoided. 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 refraction」の詳細全文を読む スポンサード リンク
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