Engineering wave reflections with power flow-conformal metamirrors | 2/22/2019 | Staff
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Metasurfaces are two-dimensional (2-D) metamaterials that can control scattering waves of a light beam. Their applications include thin-sheet polarizers, beam splitters, beam steerers and lenses. These structures can control and transform impinging waves based on the generalized reflection and refraction law (GSL; generalized Snell's law and generalized reflection law), which states that small phase-shifting elements can control the directions of the reflected and transmitted waves.

In a recent study, Ana Díaz-Rubio and co-workers in Finland and the U.S. investigated reflective metasurfaces known as metamirrors. The work was based on power flow distribution and the adaptation of the reflector shape to engineer the desired distributions of incident and reflected fields, resulting in highly efficient metamirrors. The work investigated anomalous reflection and beam splitting for both acoustic and electromagnetic waves, and the results are now published in Science Advances.

Scientists - Physics - Wave - Transformation - Metasurfaces

It was only recently that scientists understood the physics of wave transformation by metasurfaces. To understand the difficulties of controlling reflections from metasurfaces, scientists considered power flow in the vicinity of anomalous reflectors. For instance, in theory, there will be regions where the power carried by the incident and reflected waves of interest "enter" the metasurface and regions where power "emerges" from the surface. The phenomena indicated that metasurfaces required periodically distributed gain/loss response or strongly nonlocal behavior. To achieve this in practice, scientists can carefully engineer the surface resistance profile of materials for high-efficiency reflections in arbitrary directions.

Furthermore, two reflected waves can be simultaneously controlled to fully engineer wave reflections. Previous work had shown that the design of phase-gradient metasurfaces based on generalized reflection law—had higher efficiencies if the deflection angle did not exceed 40 to 45 degrees. To design highly efficient devices such as holograms or lenses, multiple reflected waves must be controlled without parasitic reflections. As a power-guiding mechanism, scientists have previously...
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