Fig. 2: Phase controllability of the unidirectional guided wave.
From: Unidirectional guided-wave-driven metasurfaces for arbitrary wavefront control
a Schematic diagram of waveguides supporting type-I and type-II USMPs at microwave frequencies, and (b) the dispersion relations of USMPs for various thicknesses of the dielectric layer. The shaded rectangular area indicates the unidirectional frequency window for the waveguide, and the other shaded areas indicate the zones of bulk modes in the gyromagnetic materials (εm = 15). Inset: simulated electric-field intensity distribution excited by a line current source placed in the middle of waveguide structure with d = 0.06λm and frequency ω = 0.75ωm. c Left: photograph of the fabricated waveguide sample. Right: photograph of the measurement configuration. d Simulated (solid) and measured (dashed) S21 and S12 parameters of the waveguide sample displayed in (c). e Schematic picture of the periodically uniform metasurface formed by alternating type-I and type-II waveguides shown in (a). The period length, duty cycle, and dielectric-layer thickness are denoted by p, a/p, and d, respectively. The phases of extracted waves from two neighboring meta-cells are φi and φi+ 1 with a difference Δφ. f Pseudocolor map of simulated neff = Δφcl/(k0p) for the structure of (e) in a parameter space spanned by dielectric thickness (d) and duty cycle (a/p) at 2.69 GHz. The three black lines indicate neff covering [ − 1, 1] range. The black stars indicate the theoretical results obtained from Eq. (4).
