Achieving asymmetry and trapping in diffusion with spatiotemporal metamaterials

• Published in: Nature communications Vol. 11; no. 1; p. 3733
• Main Authors: Camacho, Miguel, Edwards, Brian, Engheta, Nader
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 24.07.2020; Nature Publishing Group; Nature Portfolio
• Subjects: 639/166/987; 639/624/399/1015; 639/766/25; Antisymmetry; Asymmetry; Diffusion; Electrical resistivity; Flow velocity; Humanities and Social Sciences; Inversion; Metamaterials; multidisciplinary; Parameters; Science; Science (multidisciplinary); Spatial distribution; Switches; Thermal management
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-020-17550-5

The process of diffusion is central to the ever increasing entropic state of the universe and is fundamental in many branches of science and engineering. Although non-reciprocal metamaterials are well developed for wave systems, the studies of diffusive metamaterials have been limited by their characteristic spatial inversion symmetry and time inversion antisymmetry. Here, we achieve large spatial asymmetric diffusion characteristics inside a metamaterial whose material parameters are space- and time-modulated. Inside such a spatiotemporal metamaterial, diffusion occurs as if the material had an intrinsic flow velocity, whose direction is dictated by the relative phase between the modulations of the conductivity and capacity. This creates dramatic out-of-equilibrium concentrations and depletions, which we demonstrate experimentally for the diffusion of electric charges in a one-dimensional electrical system composed of an array of space-time-modulated variable capacitors and switches. These results may offer exciting possibilities in various fields, including electronics, thermal management, chemical mixing, etc. Being able to manipulate the temporal evolution and spatial distribution of diffusive quantities would provide exciting possibilities for applications. Here, the authors show that one can achieve large spatial asymmetric diffusion characteristics inside a metamaterial whose material parameters are space- and time-modulated.