| Electromagnetic metamaterials are artificial structures whose special physical properties come from the resonances of various subwavelength meta-atoms,such as the LC resonances of metallic split-ring resonators and the Mie resonance of dielectric particles.The dielectric-based Mie resonators have low heat dissipation and are widely used in metamaterial design.These meta-atoms can further constitute metamolecules,and produce near-field coupling effects.The Fano resonance is a quantum effect with a nonLorentzian spectrum,which originated from the constructive and destructive interference in the near field.It usually has a high quality factor and an extremely localized near-field,so it can enhance the electromagnetic responses of metamolecule and has a potential for sensing and near-field imaging applications.The active tunability of Fano resonance is important for its applications.Meanwhile,Fano resonance is closely related to symmetry breaking and can be used to design metamaterials with non-reciprocity or asymmetric transmission.Therefore,this thesis aims to realize the construction of several Fanoresonant metamolecules using dielectric-based Mie resonators,investigate their intrinsic physical mechanism,and explore the modulation of various parameters on their responses.On this basis,a magnetically tunable Fano resonance has been achieved,and a metamolecule with enhanced non-reciprocity has been designed using Fano mode.Besides,an all-dielectric metamaterial with asymmetric transmission has been demonstrated.The main contents and innovations of this paper are as follows:Based on the coupling effect between the metallic split-ring resonator and the Mieresonant dielectric particle,a Fano-resonant hybrid metamolecule has been designed with a quality factor of 96,which realizes the modulation and the performance enhancement of the 1st-order Mie resonance.The design can lower the requirements on the dielectric material.The Fano peak can also be adjusted by controlling the Mie resonance,and the response of metamolecules to temperature change is verified experimentally.Based on the model of ferrite’s permeability,a coupled metamolecule composed of a YIG ferrite cuboid and a Mie-resonant dielectric cube has been designed to achieve the magnetically tunability for the Fano resonance and the Mie resonance,in which Fano resonance shows a greater tunability.By further modification of this structure,the nonreciprocity enhancement near the Fano resonance has been realized.The phenomenon is narrow-banded,which shows a unidirectional transmission with a frequency selection.Such metamolecule has high design freedom,and their electromagnetic responses can be optimized by multiple methods,such as changing the dielectric constant,the saturation magnetization,and the dimensions.This metamolecule can be used to design dynamically controlled magnetic switches and isolators.Based on the theory of asymmetric transmission,an all-dielectric chiral metamaterial consisting Mie-resonant cuboids has been designed.The simulation demonstrates that the metamaterial has a dual-band asymmetric transmission of linearly polarized wave,which can achieve the conversion of the polarization of the incident electromagnetic wave.The internal and intermolecular coupling of the metamolecule can affect the electromagnetic response of the metamaterial.The asymmetric transmission at the lower frequency is generated by the coupled Fano mode and is verified by experiments.The proposed Miebased metamaterial has a simple structure,and can be applied as polarization-controlled devices. |
