ESM_File_Fig4 from A tunable electromagnetic metagrating

We explore electromagnetic (EM) wave incidence upon gratings of reconfigurable metamaterial cylinders, which collectively act as a metagrating, to identify their potential as reconfigurable subwavelength surfaces. The metacylinders are created by a closely spaced microstructured array of thin plates that, in the limit of small inter-plate spacing, are described by a semi-analytical continuum model. We build upon metacylinder analysis in water waves, translating this to EM for TE polarization (longitudinal magnetic field) for which the metacylinders exhibit anisotropic scattering; this is exploited for the multiple scattering of light by an infinite metagrating of uniform cylinder radius and angle, for which we retrieve the far-field reflection and transmission spectra for plane-wave incidence. These spectra reveal unusual effects including perfect reflection and a negative Goos–Hänchen shift in the transmitted field, as well as perfect symmetry in the far-field scattering coefficients. The metagrating also hosts Rayleigh–Bloch surface waves whose dispersion is contingent on the uniform cylinder angle, shifting under rotation towards the light-line as the cylinder angle approaches the horizontal. For both plane-wave scattering and the calculation of the array-guided modes, the cylinder angle is the principal variable in determining the wave interaction, and the metagrating is tunable simply through rotation of the constituent metacylinders.本研究探究了可重构超材料（metamaterial）圆柱光栅（整体构成超光栅（metagrating））在电磁波（electromagnetic, EM）入射下的特性，以验证其作为可重构亚波长表面的应用潜力。该超圆柱由间距紧密的薄板微结构阵列构成，当板间距足够小时，可通过半解析连续介质模型对其进行描述。本研究借鉴水波领域的超圆柱分析方法，将其推广至TE极化（纵向磁场）下的电磁波场景，此时该超圆柱呈现各向异性散射特性；基于该特性，我们针对由半径与角度均一致的圆柱构成的无限大超光栅的光多散射问题展开研究，获取了平面波入射下的远场反射与透射光谱。该光谱展现出多项反常特性，包括全反射现象、透射场中的负古斯-汉森（Goos–Hänchen）位移，以及远场散射系数的完美对称性。该超光栅还支持瑞利-布洛赫表面波，其色散特性由圆柱的均匀角度决定；随着圆柱角度趋近水平，该表面波随圆柱旋转逐渐向光锥线偏移。无论是平面波散射问题还是阵列导模的计算，圆柱角度均为决定波相互作用的核心变量，且仅通过旋转组成超圆柱即可实现超光栅的可调谐性。