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A usually artificial material that exhibits special properties not normally found in nature, such as a negative index of refraction, in its interaction with electromagnetic radiation, sound, or other wave phenomena. Such properties are a consequence of the metamaterial's structure at the microscopic or macroscopic level, rather than of the underlying properties of its components.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
(General Physics) any artificial material created from microscopic arrangements of existing elements in a structure which gives the material unconventional properties, esp when used for cloaking light or sound waves
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014