Omnidirectional zero- gap in symmetrical Fibonacci sequences composed of positive and negative refractive index materialsH. Y. Zhang, Y. P. Zhang, T. Y. Shang, Y. Zheng, G. J. Ren, P. Wang and J. Q. YaoEur. Phys. J. B, 52 1 (2006) 37-40DOI: https://doi.org/10.1140/epjb/e2006-00275-9