A metamaterial is a type of artificially engineered material that typically features a pattern or periodic arrangement of a material. Metamaterials are characterized by the fact that they take on specific macroscopic physical properties based on their structure or the pattern in which the material is arranged, but not necessarily the composition of the material. Another way to say this is that the elemental makeup of a metamaterial is not as important as the internal structure of the metamaterial. By relying on the structure of the material to influence its properties, metamaterials have been able to achieve properties that haven’t been achieved in other types of materials. One example includes materials with a negative refractive index (see “Physical and Theoretical Chemistry”), which have been able to achieve the first demonstrations of “invisibility cloaking” over certain wavelength ranges, and this technology will hopefully continue to progress as time goes on.