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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