The Realization And Properties Of Magnetic Toroidal Moment In Splitring Resonators

Electromagnetic metamaterial can realize electromagnetic phenomenon that can not be achieved by natural materials. Its electromagnetic modulation mechanism mainly stems from its spatial structure. As compared to planar metamaterial, stereometamaterial can fully utilize the 3D degrees of freedom to exploit the coupling and hybridization between resonant modes. When adopting multiple split ring resonators(SRRs), the three-dimensional structure enables more extraordinary resonances and properties. In this thesis, we propose and study a kind of structure based on connected SRRs sharing their gap in a rotational fashion. It shows that there are three typical resonant modes in such cage-like SRR(C-SRR) aggregated stereometamaterial in the communication and near infrared range and realizes toroidal response that is often ignored. We systematically study the fundamental and higher-order resonance modes in the C-SRRs and the associated electromagnetic characters of magnetic toroidal dipole moment and other multipole moments.Based on the finite element method, we firstly study the fundamental and the second-order resonant characteristics of both symmetric and asymmetric SRRs. The characteristics of electrical resonance and magnetic resonance are analyzed by the amount of radiating energy of electric dipole moment and magnetic dipole moment. According to the surface current distribution in the SRR, we discuss the formation mechanism of the multipole moments.C-SRR resonance characteristics are then studied. It is shown that there are two obvious resonances in the communication and near infrared range and an unidentified resonance peak in the visible. These modes can be ascribed to magnetic toroidal dipole, magnetic dipole and a mixture of electric dipole and toroidal dipole. According to the distribution of SRRs surface current, the latter two resonance modes are shown to be derived from the second order resonance mode in the corresponding individual SRR, while the first one is generated from the fundamental one.For the highest energy mode in C-SRR, due to its high order feature and the rotational symmetry, it remains relatively “dark”. But a C-SRR array can offer multiband filtering functionality. By altering the period and the gap, one can control the position of resonance peaks and the size of transmittance.These results provide a good platform for studying electromagnetic property of magnetic toroidal resonance and toroidal dipole, and are useful for the study of higher order magnetic resonance and the hybridization between high modes.