Metamaterialsa

Metamaterialsa is not a standard term in the scientific literature; this article uses metamaterials, the established field, to describe artificial structures that control waves in novel ways.

Metamaterials are engineered composites whose macroscopic properties derive from carefully designed subwavelength structures rather than from the base materials alone. By arranging resonant elements on scales smaller than the wavelength of interest, metamaterials can exhibit effective parameters not found in natural materials, such as a negative refractive index, strong dispersion, or tailored impedance.

Metamaterials span several domains. Electromagnetic metamaterials operate from microwave to optical frequencies and can steer light in unusual ways. Acoustic metamaterials control sound waves, enabling unusual sound transmission and focusing. Mechanical metamaterials affect stress, density, and deformation, while thermal metamaterials aim to manage heat flow. A related class, metasurfaces, consists of two-dimensional arrays that shape wavefronts with thin, flat layers.

Design principles involve homogenization of complex structures into effective medium properties. Typical unit cells include resonant rings, wires, or other inclusions arranged periodically or quasi-periodically. The resulting collective response yields tailored permittivity, permeability, or elastic and thermal parameters, depending on the domain.

History notes that the concept originated with Veselago in 1967, who theorized materials with negative index, followed by experimental demonstrations in the early 2000s. Since then, research has expanded across frequencies and applications, with ongoing efforts to reduce losses, broaden bandwidth, and enable practical devices such as super-resolution lenses, cloaking-inspired components, compact antennas, and programmable metasurfaces.

Current challenges include fabrication at small scales, material losses, and sensitivity to imperfections. Advances continue in tunable, active, and broadband metamaterials aimed at real-world deployment.