Microwave characterization of exotic resonant states in dielectric resonators

In this study, we design a structure consisting of the radial arrangement of several vertically standing dielectric disks (resonators) so that such a ring cluster supports exotic toroidal dipole mode excitation. Subsequently, the characteristics of a system composed of two identical rings with a change in the distance are studied to reveal how to affect the peculiarities of the coupling between two toroidal dipole modes. The manifestation of toroidal dipole coupling is confirmed by checking the extinction cross-section, near-field distributions, and induced toroidal moments obtained from both full-wave numerical simulation and microwave experiments. To experiment, particles are made from commercially available ceramics. During the measurements, standard microwave equipment is used to characterize the toroidal dipole coupling within the frequency band of 1−10 GHz. Since the structure comprises simple dielectric disks without any metallic elements, the proposed designs are hopefully scalable down to the micrometer or nanometer scale considering their practical applications as building blocks in metamaterials operated on the radiation-less exotic toroidal and anapole states.