Ultrawideband fractal metamaterial absorber made of nickel operating in the UV to IR spectrum

Nano-structure based metamaterial absorbers have been getting enormous interest owing to their widespread applications in solar cells, thermal emitters and integrated photonic devices. This paper presents a novel and ultrathin broadband metamaterial absorber comprised of a hexagonal nano-ring shaped fractal structure. The designed fractal metamaterial absorber (FMA) is composed of a three-layer device having a metal-insulator-metal (MIM) configuration. Based on the numerical simulations, the proposed FMA manifests more than 97% absorptivity for the operating wavelength from 820 to 2520 nm. However, it shows above 80% absorption value for the entire operating wavelength from 200 to 4000 nm. To predict the angular stability of this broadband absorption device, the absorptivity was investigated under different oblique incident angles of the exciting wave by considering both transverse electric (TE)- and transverse magnetic (TM)-polarization. Further, multiple reflection theory was employed to calculate the absorption value of FMA, and it shows appreciable agreement with the simulation results. It is also anticipated that this kind of FMA has not been investigated yet with these ultrabroadband absorption characteristics. Large operating bandwidth, angular robustness, ultra-compact thickness and inclusion of low-cost and temperature-endurable nickel metal (Ni) make this nanostructure-based absorber an attractive candidate for solar photovoltaics, thermal emission, and infrared spectroscopic applications.