metastructures

Metastructures are engineered assemblies whose effective properties arise from the arrangement and interaction of subwavelength elements rather than the composition alone. They are a practical subset of metamaterials, prioritizing geometry, interfaces, and connectivity to tailor wave response.

Typically fabricated as periodic or quasi-periodic arrays of unit cells, meta-atoms, resonators, or waveguides, metastructures produce macroscopic effects when the wavelength is larger than the feature size. Through homogenization or circuit models, designers predict effective parameters such as refractive index, impedance, or stiffness. They can be implemented in two-dimensional planar formats (metasurfaces) or three-dimensional volumes.

Electromagnetic, acoustic, and mechanical waves have been manipulated using metastructures. Phenomena include anomalous refraction and reflection, beam shaping, focusing with flat lenses, polarization control, and even cloaking. In mechanical systems they enable vibration isolation and mode control. Dynamic or tunable metastructures use active components or reconfigurable elements to adjust response in real time.

Fabrication methods include lithography, additive manufacturing, and microfabrication, enabling integration with antennas, imaging systems, or sensors. Applications span wireless communications, imaging and spectroscopy, noninvasive sensing, energy harvesting, and quieting of structures. The field emphasizes performance penalties from material loss, narrow operational bandwidth, and sensitivity to fabrication tolerances.

Ongoing research aims to broaden bandwidth, add tunability, and integrate metastructures into practical devices.