It is known that the particle chain can be served as a waveguide to guide the electromagnetic wave in the subwavelength scale and the metallic particle chain can only support the transverse electric (TE) mode (the magnetic field is perpendicular to the propagation direction). In this work, the composite metal-dielectric chains are constructed as the rod arrays in form of a straight line, a zigzag edge, or a combined double chains, in which both the TE mode and the transverse magnetic (TM) mode (the electric field is perpendicular to the propagation direction) can be supported. Based on the Mie theory and multiple scattering theory, the dispersion curves for different chains can obtained rigorously so that the dependence of the edge states on the structure parameters and symmetry of the chains can be examined. As a result, the loss can be reduced and the frequency of the surface plasmon polariton can be adjusted. In addition, the idea can be further extended to composite chains composed of the dielectric and magnetic particles so that the nonreciprocal features can be modulated.
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.
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.
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