Broadband THz metasurface bandpass filter/antireflection coating based on metalized Si cylindrical rings

Abstract

The operation of the metasurface based on silicon cylindrical rings coated by a gold as a terahertz (THz) bandpass filter/antireflection structure is studied. The decrease in the reflectance is conditioned by the destructive interference of electromagnetic waves reflected from structural layers of the metasurface. An efficient antireflection band with the reflectance below 10% is formed in the frequency spectrum of 0.71 to 0.92 THz with a relative bandwidth of 26%. It is shown that the operating spectrum of the suggested metasurface can be varied by changing the total radius of cylindrical rings, whereas the filter's performance is rather insensitive to the variations in cylinder height and inner radius. The dependence of the antireflection band on the polarization and incidence angle of the THz waves is also analyzed. The antireflection band is sensitive to changes in the surrounding medium, hence supporting the use of the structure as a refractive index sensor.