Electric toroidal dipole response in split-ring resonator metamaterials L.Y. Guo, M.H. Li, Q.W. Ye, B.X. Xiao and H.L. Yang Eur. Phys. J. B, 85 6 (2012) 208 Published online: 20 June 2012 DOI: 10.1140/epjb/e2012-20935-3