ESM_File_Fig8 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.本研究探究了入射至可重构超材料圆柱光栅的电磁（EM）波，该光栅整体可作为超光栅（metagrating），旨在验证其作为可重构亚波长表面的应用潜力。该超材料圆柱（metacylinders）由间距紧密的薄板微结构阵列构成，当板间距极小时，可通过半解析连续介质模型对其进行描述。我们以水波场景下的超材料圆柱分析为基础，将其拓展至电磁领域，针对横电波（TE polarization，纵向磁场）展开研究，此时超材料圆柱呈现各向异性散射特性。我们利用该特性，针对由半径与角度均统一的圆柱构成的无限长超光栅，开展光波多重散射分析，并得到了平面波入射下的远场反射与透射光谱。这些光谱揭示了多项反常效应，包括全反射、透射场中的负古斯-汉欣位移，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，其色散特性取决于圆柱的统一角度；当圆柱角度趋近水平时，该表面波的色散曲线会随旋转向光锥线偏移。无论是平面波散射分析还是阵列导模计算，圆柱角度都是决定波相互作用的核心变量，且仅需旋转构成超光栅的超材料圆柱，即可实现对该超光栅的可调谐调控。