A metamaterial is an artificial composite that gains electrical properties based on its structure rather than directly from the materials it is made of.The properties of metamaterials are manipulated within their internal physical structure, allowing them to have an unnatural effect on light passing through them.
Metamaterials behave like an antenna would. Antennas were created to interact with radio waves and could be adjusted to modify the performance. Metamaterials work the same way within visible light wavelengths allowing engineers to interact and manipulate visible light. The artificial structures have a size and spacing that is smaller than the wavelengths of visible electromagnetic radiation. Because of this, a shorter wavelength of electromagnetic radiation, like an X-ray, is required to image and scan them. The artificial structure functions like an atom or molecule would in a normal material until it is subjected to a regulated interaction with electromagnetic radiation.
The properties of a metamaterial appear when a metamaterial interacts with electromagnetic radiation. Electric permittivity and magnetic permeability can be adjusted by tuning the spacing or size of the elements. Electrical permittivity can be altered to be a negative, zero, or to be a positive at a specific wavelength. Artificial magnetism can be achieved by adjusting the magnetic dipole in or out of phase with an external oscillating field, creating a positive or negative magnetic permeability. When electric permittivity and magnetic permeability are both negative, materials can be created with a negative refractive index.
When light passes from a positive-index medium to a negative-index medium, the light is bent negatively at the interference between the two media, and a negative refraction occurs. Materials with a negative-index aren't existent in nature. In 2001, Robert Shelby, and American physicist, first experimented with the phenomenon with microwave wavelengths. The phenomenon has now been studied at visible wavelengths.
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Metamaterials - an overview | ScienceDirect Topics