Metamateriale

Metamaterials are artificial materials engineered to have properties that do not occur in naturally occurring substances. Their unusual behavior derives not primarily from chemical composition but from carefully designed micro- or nano-structures arranged in periodic or quasi-periodic patterns. When the feature size is smaller than the wavelength of the relevant waves, the ensemble can be described by effective parameters such as permittivity, permeability, or elastic moduli that are not found in ordinary materials.

Electromagnetic metamaterials manipulate radio, microwave, terahertz, and optical waves. Typical unit cells, often called resonators, are much smaller than the wavelength and may include elements like split-ring resonators or wire pairs. Such structures can produce a negative refractive index, strong anisotropy, or cloaking effects through anomalous phase and amplitude control.

In addition to electromagnetism, acoustic metamaterials control sound waves; mechanical metamaterials affect vibrations and mechanical properties; thermal metamaterials constrain heat flow. The concept of metamaterials is to achieve effective parameters that are impossible with bulk materials alone.

Historical notes: the theoretical idea of a material with negative index of refraction was proposed by Victor Veselago in 1967. Practical demonstrations emerged in the early 2000s, with microwave metamaterials showing negative refraction and cloaking experiments on a small scale.

Applications include super-resolution imaging (superlenses), compact and reconfigurable antennas, waveguides and cloaking concepts, sound insulation, and protective materials against vibrations. Researchers continue to address challenges such as inherent losses, narrow operational bandwidths, fabrication complexity, and difficulties scaling to optical frequencies.

Metamaterials represent a rapidly evolving interdisciplinary field with ongoing work to broaden bandwidth, functionality, and manufacturability.