Ultra-broadband reflectionless Brewster absorber protected by reciprocity

摘要

a Illustration of the Brewster effect between a background dielectric εb and a nonmagnetic TAM. Due to the protection of reciprocity, the wave impedance in the left case θi>0 is exactly the same as that in the right case θi<0. The transmission in the right (left) case is dependent (independent) on εy′. The upper plane of EFCs of the background dielectric (black solid lines), and the lower plane of EFCs of the TAM when εx′ and α are fixed but εy′ is varied (color solid lines), regarding the cases of bεx′≠εb and eεx′=εb, respectively. The colors denote the magnitude of wave impedance Z. The black dashed vertical lines are the equal-Z lines, which intersect with the EFCs at points I and II, respectively. The gray arrows denote the wave vectors of the incident and reflected beams determined by the EFCs of the background dielectric, and the red and green arrows denote the refracted beam determined by the EFCs of the TAM. Calculated reflectance as functions of θi and εy′ for TM-polarized waves incident from free space onto the TAM with cεx′=2 and α=35.3∘, or fεx′=1 and α=30∘, respectively. Simulated distributions of magnetic fields (color) and group velocity (arrows) for the TAM with dεx′=2 and α=35.3∘ under θi=54.7∘ (left) or θi=−54.7∘ (middle and right), or gεx′=1 and α=30∘ under θi=30∘ (left) or θi=−30∘ (middle and right), respectively. We set εy′=3 (left and middle) or εx′=−3 (right).