Metamaterials are materials engineered to have properties that have not yet been found in nature. They are made from assemblies of multiple elements fashioned from composite materials such as metals and plastics. These materials are usually arranged in repeating patterns at scales that are smaller than the wavelengths of the phenomena they influence. Their precise shape, geometry, size, orientation and arrangement gives them their smart properties capable of manipulating electromagnetic waves: by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials.
The concept dates back to the late 19th century with work by Jagadish Chandra Bose on microwave polarization, but the field exploded in the 2000s after David Smith and colleagues at Duke University produced the first metamaterial with a negative refractive index, confirming Victor Veselago's 1968 theory.
Metamaterials are used in high-gain antennas, super-lenses (which can image below the diffraction limit), and seismic protection (shielding buildings from earthquakes). They are famously known for their potential to create 'invisibility cloaks' that bend light around an object.