| Metamaterials is a kind of artificial composite material which is composed of an array of subwavelength resonant building blocks arranged in a periodic or nonperiodic configuration.It exhibits a lot of exotic electromagnetic properties that are not possessed by natural materials,thus enables flexible manipulation on the magnitude,polarization,phase,frequency and other parameters of electromagnetic waves.In a two-dimensional system,the Maxwell's equations have two sets of independent solutions,namely,transverse electric mode(TE mode: the electric field lies in the incident plane)and transverse magnetic mode(TM mode: the magnetic field lie in the incident plane).In this dissertation,a single-layer magnetic metamaterial composed of an array of ferrite rods positioned periodically in the air is constructed,based on which the electromagnetic beams with both TE and TM polarizations are regulated separately.In addition,by further tuning either the magnitude of the bias magnetic field or the structure parameters the outgoing beams can be flexibly controlled,adding more degree of freedoms in beam steering.The contents of the dissertation are organized as follows:In chapter one,a brief introduction on the history,the electromagnetic properties,the research status as well as the application prospect of photonic crystals,metamaterials,and magnetic metamaterials are presented.In particular,the exotic properties and phenomena of magnetic metamaterials arising from its intrinsic magnetic response and tunability are sketched.In chapter two,the physical model and the theoretical method are introduced,including the Mie theory for the scattering of a single ferrite rod and the multiple scattering theory for the simulation of the scattering field,the transmittance,the reflectance,the partial wave scattering amplitude and phase of an array of ferrite rods.In chapter three,the electromagnetic beam steering by the single-layer magnetic metamaterial with three different sets of parameters are considered and the TE and TM polarizations can be controlled intrinsically by the configurations and extrinsically by the bias magnetic field,respectively.Case 1: the negative transmission happens for the TE polarization and for the TM polarization the scattering field is switched from the total reflection to the negative transmission by tuning the bias magnetic field.Case 2: the primary transmission happens for the TE polarization for the TM polarization the scattering field is switched from the negative transmission to the total reflection.Case 3: the total reflection happens for the TE polarization and for the TM polarization the scattering field is switched from the primary transmission to the total reflection.Due to the single-layer feature of the magnetic metamaterial,the phenomenon can be understood by calculating the amplitude and phase of the partial wave scattering for the single rod and the rod in the array,which indicates that the partial wave scattering associated with 0,+1,-1 orders and the phase difference between the adjacent rods play the crucial role.In chapter four,the nonreciprocity corresponding to the first and the second order resonances are analyzed by calculating the Mie scattering coefficients of a single rod and the partial wave scattering of the rod in the array,which indicates that the combined action of the 0,+1 and-1 orders Mie resonance is responsible for the first-order nonreciprocity and the second-order nonreciprocity is attributed to the combined action of the 0,+2 and-2 orders Mie resonances.The nonreciprocity can also be manifested by reversing the bias magnetic field so that the outgoing beam can be switched from one status to another status.In addition,it is shown that the negatively transmitted beam can be deflected from the symmetric direction in a certain range by tuning the structure parameters.In the last chapter,the conclusion is summarized and the outlook on the structure optimization as well as the further beam steering is also presented. |
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