Electric toroidal dipole response in split-ring resonator metamaterials

Toroidal dipoles are usually masked by other stronger effects of classical electric and magnetic multipoles, such as dipoles, quadrupoles, octupoles and so forth. So observation of the toroidal response is extremely rare. For the first time we present an electric toroidal dipole model based on metamaterials, which is composed of split-ring resonators. The transmission and reflection spectra show that there are two resonances at the frequency of 5.0 GHz and 11.2 GHz. Calculated radiated power dispersion for various multipole moments derived from the current density proved that these two resonances are electric dipole response and elusive electric toroidal dipole response respectively. Our experimental evidence of electric toroidal dipole response brings attentions to the often ignored toroidal multipoles.