Adjustable low frequency and broadband metamaterial absorber based on magnetic rubber plate and cross resonator J. Appl. Phys. 115, 064902 (2014); 10.1063/1.4863540Integrating non-planar metamaterials with magnetic absorbing materials to yield ultra-broadband microwave hybrid absorbers Appl. Phys. Lett. 104, 022903 (2014); 10.1063/1.4862262 Ultra-broadband electromagnetically induced transparency using tunable self-asymmetric planar metamaterials J.This paper presents a type of isotropic broadband metamaterial absorber comprising single-layer densely arranged hexagonal metal dendritic units having different sizes printed on an FR-4 dielectric substrate with a metallic film coating. The convergence of the different neighboring resonant frequencies of the differently sized units yields broadband absorption characteristics. In the case of normal incidence, the absorber operating in the X-band yields absorption rates greater than 80% in the frequency range from 9.05 GHz to 11.4 GHz, this reasonable absorption performance is maintained for oblique incidences less than 45 . The S-band absorber has an absorptivity of more than 50% in the frequency range from 3.02 GHz to 4 GHz. The experimental results demonstrate that the interaction between the different structural units is not obvious. V C 2013 AIP Publishing LLC.

Metamaterials are composed of periodic or quasi‐periodic subwavelength structures, having electric and/or magnetic responses. Metamaterials can arbitrarily tailor the refractive index by artificially tailoring the unit‐cell geometries and dimensions. Recent years, as the two dimensional equivalent of bulk metamaterials, metasurfaces have caused considerable attentions due to the lower profile and simpler to fabricate than bulk metamaterials. Metasurfaces can impart discontinuities on electromagnetic wavefronts and can achieve the arbitrary transmission phase of the whole period range. Metamaterials and metasurfaces have led to the realizations of novel electromagnetic properties and functionalities through tailoring subwavelength structures and integrating functional materials. In this letter, two planar lenses are respectively proposed to control the beam direction of the horn antenna by using a gradient refractive index (GRIN) metamaterial and a gradient phase (GRPH) metasurface. It is shown that the antenna beam direction can be steered by controlling the refractive index of the GRIN metamaterial or the transmission phase of the GRPH metasurface. The differences between the two planar lenses for controlling the antenna beam are illustrated.