Ultrabroadband absorber based on a funnel-shaped anisotropic metamaterial

A design of a funnel-shaped anisotropic metamaterial absorber is reported with a periodic array of nickel–germanium (Ni/Ge). The optical properties of the suggested anisotropic metamaterial absorber are numerically calculated using the 3D finite-difference time-domain technique. Composed of both cylindrical and conical units, the reported anisotropic metamaterial attains high absorption over a wavelength range from 200 nm to 9000 nm with an average absorption of 96%. A wide wavelength absorption band is achieved from the ultraviolet to near infrared including the visible range. The cylindrical unit could harvest low-order modes, while the longer wavelengths are trapped through the conical part. The enhanced broadband absorption is due to the excitation of multiple orders of slow-light modes. In addition, the effect of the incident angle on the absorption of transverse magnetic and transverse electric-polarized waves is also investigated. Further, the structural geometrical parameters are studied in order to maximize the absorption through the proposed design.