  In this paper, mu-near-zero (MNZ) metamaterials are utilized to achieve an
ultrathin absorber with a thickness of only about one percent of the operating
wavelength. The metamaterial absorber (MA) is made of double-layered metallic
spiral arrays designed to have a large purely imaginary permeability at low
microwave frequencies (~ 1.7 GHz). An absorption efficiency above 90% is
demonstrated at illumination angles up to 60 degrees. A
polarization-insensitive MA implemented by 2D isotropic metamaterials is also
studied. Our designs have great application potential as compared with the
traditional heavy and thick absorbers made of natural materials working at the
same frequencies.
