A Tuneable Electromagnetic Metagrating


H.J. Putley, S. Guenneau, R. Porter & R.V. Craster (submitted to Proc Roy Soc Lond A. June 2022)


We explore electromagnetic (EM) wave incidence upon gratings of reconfigurable metamaterial cylinders, that collectively act as a metagrating, to identify their potential as reconfigurable subwavelength surfaces. The metacylinders are created by a closely-spaced microstructured internal 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 and internal trapping; these features are 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 even under non-normal incident angle. The metagrating also hosts exclusively symmetric 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 tuneable simply through rotation of the constituent metacylinders.

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