Even highly absorbent surfaces can become very reflective when the angle of incidence is steep. For example, an asphalt road will reflect sunlight late in the day when the sun is low. Controlling higher order spatial harmonics reflected from a surface is important for many civilian and military applications, but it is particularly challenging technically for steep angles of incidence. For over a decade, highly efficient wideband retroreflecting metasurfaces have been studied without producing satisfactory results.

Recently published results for a class of metamaterials called binary Huygens metasurfaces, however, show promise to address this long-standing challenge in the control of spatial harmonics. Their results, however, are for only a single polarization and narrow angular and frequency range. Georgia Tech’s new techniques extend the concept of array-based binary metasurfaces to dual polarization and increase both frequency and angular bandwidth.

These retroreflective metastructures are made up of several metasurface arrays for enhanced retroreflective electromagnetic responses. There are several possible designs using stacked or side-by-side configurations to achieve features such as dual polarization, dual band, or broadband. The designs also offer varying efficiency levels. For example, a stacked metastructure offers higher efficiency, while a side-by-side configuration is less efficient but offers simpler construction and more flexibility.