Cross-Shaped Titanium Resonators Based Metasurface for Ultra-Broadband Solar Absorption

We propose a scheme for ultra-broadband and polarization-insensitive metamaterial perfect absorber (PA) by utilizing a thin metal-insulator-metal (MIM) stack, which is comprised of an array of cross-shaped titanium resonators, a silica dielectric spacer, and an opaque titanium slab. The bandwidth of absorption (A) > 90% is up to 2100 nm, ranging from the visible to near infrared region. At the wavelength range of 400-2500 nm, this metamaterial absorber shows strong absorption of electromagnetic waves. The spectral average absorptivity reaches 93.8% and the maximal absorptivity is up to 99.8%. In addition, the simulations show that the absorption remains high over a broad range of incident angles. Additionally, we have investigated the influences of geometries, structural parameters and material features on the absorption properties. The utilization of titanium rather than the noble metals efficiently lowers the fabrication cost and enhances the thermal stability and biocompatibility, thus paving a way to numerous applications such as solar energy harvesting, imaging, infrared detection and bio-medical techniques.