Spatiotemporal Isotropic-to-Anisotropic Meta-Atoms

TL;DR

This paper introduces spatiotemporal meta-atoms with time-dependent properties that enable dynamic control of electromagnetic wave scattering, offering new possibilities for real-time wave manipulation in advanced metamaterials.

Contribution

It proposes the concept of isotropic-to-anisotropic spatiotemporal meta-atoms and demonstrates their ability to manipulate wave directions through rapid permittivity changes.

Findings

Scattered wave directions depend on the anisotropic permittivity tensor.

Numerical studies show control over wave scattering by varying permittivity and geometry.

Asymmetric wave response enables real-time wave manipulation.

Abstract

Metamaterials and metasurfaces are designed by periodically arranged subwavelength geometries, allowing a tailored manipulation of the electromagnetic response of matter. Here, we exploit temporal variations of permittivity inside subwavelength geometries to propose the concept of spatiotemporal meta-atoms having time-dependent properties. We exploit isotropic-to-anisotropic temporal boundaries within spatially subwavelength regions where their permittivity is rapidly changed in time. In so doing, it is shown how resulting scattered waves travel in directions that are different from the direction of the impinging wave, and depend on the values of the chosen anisotropic permittivity tensor. To provide a full physical insight of their performance, multiple scenarios are studied numerically such as the effect of using different values of permittivity tensor, different geometries of the spatiotemporal meta-atom and time duration of the induced isotropic-to-anisotropic temporal boundary. The intrinsic asymmetric response of the proposed spatiotemporal meta-atoms is also studied demonstrating, both theoretically and numerically, its potential for an at-will manipulation of scattered waves in real time. These results may open new paradigms for controlling wave-matter interactions and may pave the way for the next generation of metamaterials and metasurfaces by unleashing their potential using four-dimensional (4D) unit cells.