Based on the Mie theory and the multiple scattering theory, we have performed a comparative study on the beam steering by two kinds of systems which are composed of either a single layer of dielectric rods or a single layer of ferrite rods. It is shown that for both systems the incident Gaussian beam can be negatively refracted and with appropriate adjusting the related parameters the total reflection can be implemented as well. However, the essences to realize the phenomena are different with the former system keeping the reciprocal property and the latter one exhibiting nonreciprocal property. For the dielectric system, to switch the functionality the resonance is tuned by the size of the dielectric rod, while for the magnetic system it is realized by simply reversing the bias magnetic field due to the nonreciprocity of the ferrite materials under the bias magnetic field (BMF). By examining the field profiles we can find more details, where the dielectric system is operable for the transverse electric (TE) mode and the magnetic system is effective for the transverse magnetic (TM) mode. The electromagnetic field patterns associated with the single dielectric rod and ferrite rod exhibit different forward and backward scattering features in case of negative refraction and total reflection, which is further enhanced by the constructive and destructive interference of scattering fields from the all the rods in the particle array. The results are significant for the understanding of resonance in reciprocal and nonreciprocal systems and also inspiring for the flexible beam steering.
Based on the multiple scattering theory and effective medium theory, we demonstrate that flexibly molding the propagation of electromagnetic waves can be realized by designing magnetic metamaterials (MMs) with an array of ferrite rods. By calculating photonic band diagrams and effective constitutive parameters, it is shown that MMs can be used to achieve effective zero index with both the effective permittivity and permeability close to zero, a matched zeroindex material (MZIM). The transmitted Gaussian beam exhibit zero phase delay when it pass through the MZIM slabs with different thicknesses so that the spatial phase change of electromagnetic waves can be regulated, thereby realizing a diversity of electromagnetic wave-front modulation. In particular, the effective index of MMs can be tuned from negative to zero and to positive by controlling bias magnetic field (BMF), resulting in the switching of beam reflection and refraction. The working frequency of MZIM can also be tuned by controlling BMF, adding additional degree of freedom. Moreover, the gradient index MM can be realized by applying a gradient BMF, which can provide an additional parallel wave vector so that the direction of transmitted beam can be controlled more flexibly by controlling the gradient of BMF, which is more convenient for the designing electromagnetic devices.
Based on the multiple scattering theory and Mie theory, we have investigated two types of electromagnetic systems with broken symmetries, which are used to manipulate the propagation of electromagnetic waves. The former one is magnetic metamaterial made of an array of ferrite rods arranged either in periodic or non-periodic configurations, which bears the time-reversal-symmetry (TRS) breaking by applying a bias magnetic field. It can act as a perfect unidirectional absorber that can absorb the incident beam at a specified direction completely, while reflect nearly one half of the incident beam at the symmetrically opposite direction. The underlying physics lies in the excitation of magnetic surface plasmon that behaves differently for various incident directions. The phenomenon can also be understood by calculating the photonic band diagrams and effective constitutive parameters. The latter one is all-dielectric complex graded photonic crystal (GPC) consisting of dielectric rod dimers with a rotational gradient introduced layer by layer, which therefore breaks the spatial inversion symmetry of the system. The GPC is shown to split the incident beam into two separate ones, while for the light beam incident from opposite direction the focusing effect can be observed. The phenomenon can be interpreted by calculating the photonic band diagrams and iso-frequency curves. By tuning the gradient, the performance and the efficiency can be further controlled. The comparative study of configurations with two kinds of broken symmetries is significant for the understanding unidirectional wave propagation and the design of related electromagnetic devices.
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