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Metamaterials are materials with unique properties based on their structure, rather than chemical composition. Negative refractive index metamaterials can bend light in unusual ways, with potential applications in superlenses and invisibility cloaks. They are often used in optics and electromagnetism and are associated with nanotechnology. Opal is a natural metamaterial with unique color properties.
A metamaterial is a material with special properties derived from its structure rather than its chemical composition. The best-known metamaterial are materials with a negative refractive index, which means they bend light “the wrong way,” which is significantly more than any material with a positive refractive index.
Negative refractive index materials have applications in “superlenses” – special lenses with the potential to resolve features smaller than the wavelength of visible light and possible invisibility cloaks that direct visible light uniformly around an object rather than absorb it or reflect it in a conventional way. These materials could also be used in plasmonics, an exotic new area of computation that exploits density waves in charge carriers for computations.
Most of the metamaterials are used for electromagnetism and optics related applications, such as beam steers, modulators, band pass filters, lenses, etc. They are repeating grids of cellular components, with a cell size approximately equal to that of the wavelength of electromagnetic radiation they are trying to work with. So a metamaterial designed to redirect microwaves would have cells in the millimeter range, while a metamaterial designed for optical applications would have much smaller cells, around the 380 nm – 780 nm range.
Metamaterials are often associated with nanotechnology because the tiny repeating cell structures used for optical applications are measured in nanometres. Creating metamaterials may require new manufacturing methods, made possible only through nanotechnology. As nanotechnology progresses over the next few decades, it will unlock new metamaterials and reduce their costs.
There is at least one known natural metamaterial: opal. Opal is composed of cristobalite, a high-temperature polymorph of quartz and tridymite produced in volcanic eruptions. The resulting material consists of huge numbers of tiny mineral cells that constantly rotate in relation to each other, creating the macro-scale effect of a beautiful display of multiple colors, especially a bright blue. Researches into natural opals and metamaterial qualities are ongoing.
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