A wide-angle broadband absorber in graphene-based hyperbolic metamaterials Renxia Ning, Shaobin Liu, Haifeng Zhang, Borui Bian and Xiangkun Kong Eur. Phys. J. Appl. Phys., 68 2 (2014) 20401 Published online: 15 October 2014 DOI: 10.1051/epjap/2014140221