In our daily lives, we can find many examples of manipulation of reflected waves, such as mirrors, or reflective surfaces for sound that improve auditorium acoustics. When a wave impinges on a reflective surface with a certain angle of incidence and the energy is sent back, the angle of reflection is equal to the angle of incidence. This classical reflection law is valid for any homogenous surface. Researchers at Aalto University have developed new metasurfaces for the arbitrary manipulation of reflected waves, essentially breaking the law to engineer the reflection of a surface at will.

Metasurfaces are artificial structures, composed of periodic arranged of meta-atoms at subwavelength scale. Meta-atoms are made of traditional materials, but if they are placed in a periodic manner, the surface can have many unusual effects that cannot be realized by natural materials. In their article published 15 February 2019 in Science Advances, the researchers used power-flow conformal metasurfaces to engineer the direction of reflected waves.

“Existing solutions for controlling reflection of waves have low efficiency or difficult implementation,” says Ana Díaz-Rubio, postdoctoral researcher at Aalto University. “We solved both of those problems. Not only did we figure out a way to design high efficient metasurfaces, we can also adapt the design for different functionalities. These metasurfaces are a versatile platform for arbitrary control of reflection. This is really an exciting result. We have figured out a way to design such a device and we test it for controlling sound waves. Moreover, this idea can be applied to electromagnetic fields.”

Provided by: Aalto University  

More information: Ana Díaz-Rubio et al, Power flow–conformal metamirrors for engineering wave reflections, Science Advances (2019). DOI: 10.1126/sciadv.aau7288 

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Image: Schematic representation of the functionality implemented with the metasurface.
Credit: Aalto University