0.2 λ₀ Thick Adaptive Retroreflector Made of Spin‐Locked Metasurface

Abstract

The metasurface concept is employed to planarize retroflectors by stacking two metasurfaces with separation that is two orders larger than the wavelength. Here, a retroreflective metasurface using subwavelength-thick reconfigurable C-shaped resonators (RCRs) is reported, which reduces the overall thickness from the previous record of 590 λ down to only 0.2 λ . The geometry of RCRs could be in situ controlled to realize equal amplitude and phase modulation onto transverse magnetic (TM)-polarized and transverse electric (TE)-polarized incidences. With the phase gradient being engineered, an in-plane momentum could be imparted to the incident wave, guaranteeing the spin state of the retro-reflected wave identical to that of the incident light. Such spin-locked metasurface is natively adaptive toward different incident angles to realize retroreflection by mechanically altering the geometry of RCRs. As a proof of concept, an ultrathin retroreflective metasurface is validated at 15 GHz, under various illumination angles at 10°, 12°, 15°, and 20°. Such adaptive spin-locked metasurface could find promising applications in spin-based optical devices, communication systems, remote sensing, RCS enhancement, and so on.

A Thin Self‐Feeding Janus Metasurface for Manipulating Incident Waves and Emitting Radiation Waves Simultaneously

“…To obtain multifunction, there are great deals of literatures about the multifunctional metasurfaces. [ 22–46 ] The metasurfaces in these literatures can be divided into two categories—multifunctional metasurface with ingenious microstructure and tunable multifunctional metasurface. For the first category, the multifunction can be generally obtained in different frequencies or different spaces due to the fascinating and ingenious microstructures.…”

“…For the other category, much attention has been focused on the design of multifunctional and reconfigurable metasurfaces with tunable metaparticles driven based on thermal effects, electrically tuning, and mechanically stretching, etc. [ 31–39 ] Recently, a number of efforts have been devoted to the reconfigurable multifunctional metasurfaces by hybridizing metasurfaces with tunable metaparticles, such as the graphene, liquid crystal, vanadium dioxide, water droplet, microelectromechanical system (MEMS), liquid metal, light‐emitting diodes, PIN diodes, and varactor diodes. [ 47–60 ] However, these existing multifunctional metasurfaces are all metasurfaces for regulating the EM waves.…”

Experimental Demonstration of a 3D‐Printed Arched Metasurface Carpet Cloak

“…The top right inset of Figure c shows the scheme of the designed unit cell. The unit cell can be divided into three parts: a metallic closed ring made of liquid metal Galinstan (σ = 3.46 × 10 6 S m −1 ), a polymer substrate with a closed ring channel made by ultraviolet (UV) curable resin (ε r = 3.0, tan δ = 0.0375), and a copper foil at the back. The period p and thickness t of the unit cell are 12 mm and 3 mm, respectively.…”

Angular‐Adaptive Spin‐Locked Retroreflector Based on Reconfigurable Magnetic Metagrating

“…As a consequence, the gradient metasurface reflects photons back at a particular incident angle, but reflects other incident photons into different directions. An adaptive phase‐gradient metasurface using subwavelength‐thick reconfigurable C‐shaped resonators has been designed for tunable periodicity and multiangle performance . However, it is impossible for such metasurface to realize retroreflection under a continuous range of incidence angles, because the period of the metasurface can only be tuned to some discrete values rather than continuous ones thus limiting its practical application.…”