Brewster metasurfaces for ultrabroadband reflectionless absorption at grazing incidence

Previous reflectionless metasurfaces based on balanced electric and magnetic responses in engineered resonant meta-atoms become ineffective at oblique incident angles and usually have strong reflection at grazing incidence, where the impedance becomes near-zero or divergent. Here, by introducing the concept of anomalous generalized Brewster effect to metasurfaces, we demonstrate an exceptional resonance-free Brewster metasurface that exhibits ultrabroadband zero reflection at grazing incidence. The anomalous generalized Brewster effect is obtained via combining the mechanisms of the generalized Brewster effect and the anomalous Brewster effect, which are both resonance-free and thus enable ultrabroadband functionalities. As a practical application, Brewster metasurfaces exhibiting ultrabroadband reflectionless perfect absorption at grazing incident angles are constructed and demonstrated by full-wave simulations and microwave experiments. Our work could enable reflectionless wave manipulation at grazing incidence with an ultrawide working bandwidth.