Flat‐Knit, Flexible, Textile Metasurfaces
Michael J. Carter, Leah Resneck, Younes Ra’di, Nanfang Yu
Abstract
Lightweight, low-cost metasurfaces and reflectarrays that are easy to stow and deploy are desirable for many terrestrial and space-based communications and sensing applications. This work demonstrates a lightweight, flexible metasurface platform based on flat-knit textiles operating in the cm-wave spectral range. By using a colorwork knitting approach called float-jacquard knitting to directly integrate an array of resonant metallic antennas into a textile, two textile reflectarray devices, a metasurface lens (metalens), and a vortex-beam generator are realized. Operating as a receiving antenna, the metalens focuses a collimated normal-incidence beam to a diffraction-limited, off-broadside focal spot. Operating as a transmitting antenna, the metalens converts the divergent emission from a horn antenna into a collimated beam with peak measured directivity, gain, and efficiency of 21.30, 15.30, and -6.00 dB (25.12%), respectively. The vortex-beam generating metasurface produces a focused vortex beam with a topological charge of m = 1 over a wide frequency range of 4.1-5.8 GHz. Strong specular reflection is observed for the textile reflectarrays, caused by wavy yarn floats on the backside of the float-jacquard textiles. This work demonstrates a novel approach for the scalable production of flexible metasurfaces by leveraging commercially available yarns and well-established knitting machinery and techniques.