metamaterials

Metamaterials are artificially structured composites engineered to exhibit properties not typically found in natural materials. Their characteristics arise from designed microstructures rather than chemical composition, typically consisting of repeating unit cells smaller than the wavelengths of interest. This enables unusual electromagnetic, acoustic, or mechanical responses, such as a negative refractive index or acoustic cloaking.

Design principles rely on the arrangement and geometry of subwavelength elements, such as resonators (for example, split-ring resonators) and conducting wires. By tuning geometry and arrangement, one can tailor effective parameters like permittivity and permeability, or their acoustic and mechanical analogs. Metamaterials are often anisotropic and dispersive, with properties that depend on frequency and direction of wave propagation.

History and development trace to Vincenzo Veselago, who in 1968 predicted that materials with simultaneously negative permittivity and permeability could reverse many optical phenomena. Practical demonstrations emerged in the early 2000s, leading to rapid expansion into microwave, optical, acoustic, and mechanical domains. The field encompasses both homogeneous metamaterials and metastructures composed of repeating unit cells.

Applications span imaging, sensing, and wave control. Notable examples include superlenses that aim to beat diffraction limits, cloaking concepts, antennas with tailored radiation patterns, and transformation optics devices. More recently, metamaterials have inspired acoustic and seismic variants designed to steer or damp waves in solids and fluids.

Challenges remain, including material losses, limited bandwidth, fabrication tolerances, and scalability to optical frequencies. Ongoing research seeks robust, low-loss designs and scalable manufacturing methods to broaden practical use and integration with existing technologies. Metamaterials remain an active interdisciplinary area with potential for new devices and systems.