  We propose a thin, compact, broadband, polarization and angle insensitive
metamaterial absorber based on a tungsten reflector, silicon spacer and a top
pattern composed of a double square-like ring resonator utilizing nickel(Ni).
In such a structure, a high absorption (above 80 %) bandwidth ~ 4.8 {\mu}m from
3.52 up to 8.32 {\mu}m corresponding to the relative bandwidth ~81% can be
achieved with deeply subwavelength unit cell dimensions. Here the physical
origin of the broadband absorption is associated with low Q-factor dipole modes
of the top pattern inner and outer sides functioning as rectangular
nanoantennas. Owing to the structural symmetry, the absorber shows a good
incidence angle tolerance in the relatively wide range for both TE and TM
polarizations. The effective parameters of the Ni-based absorber were retrieved
using the constitutive effective medium theory and the absorption
characteristics of the effective medium and metamaterial were compared.
