Translated Abstract
Metasurface is generally composed of periodic sub-wavelength metallic elements printed on the substrate. Because of the electromagnetic resonance of metallic elements, some novel electromagnetic phenomena can be realized, such as polarization conversion, anomalous reflection or refraction, and surface wave coupling. These phenomena make metasurface have great potential in microwave device designs, antenna design, and sensor application, etc. The dissertation mainly presents and explains the mechanism of metasurface that can be applied to metasurface design. To be more specific, the major research work in the dissertation is presented as follows:
1) Study of the mechanism of the reflective and transmissive metasurfaces. First, the generalized Fresnel formula is proposed for the interface of the metallic elements, and the equivalent circuit method is developed to determine the corresponding expression for metallic cut-lines. Then, the tangential network transmission theory is established for reflective metasurface at oblique incidence, in which the total reflected wave can be acquired by summing multiple reflected and refracted waves. Finally, four-dimensional characteristic matrix theory is proposed for transmissive metasurface since the the series summation will be hard. In the theory, a series of four-dimension matrices are established to relate total tangential fields in different interfaces, which directly yields the total reflection and transmission matrices of the metasurface.
2）Study of the multiple band design and analytical design for polarization converter based on the metasurface. In order to expand the band of the polarization converter, anisotropic metallic structures with different sizes are combined to increase the plasmon resonance frequencies and a three-band polarization converter is realized. Simultaneously, the analytical method is established for polarization converter to improve the design efficiency. Firstly, the tangential network transmission theory is used to solve the total reflection matrix of the metasurface, which includes the electrical parameters of the metallic elements. Then, the analytical expression of the electrical parameters can be obtained by theoretical derivation or simulation fitting. Finally, the geometric parameters of the unit structure can be deduced by the total reflection matrix according to characteristic of the polarization converter.
3）Study of the Babinet principle for the complementary metasurface. The existing Babinet principle requires that the substrate should be uniform or that the periodic metallic elements should be isotropic. Three physical models are proposed for the case where the periodic complementary metallic elements are placed in the interface of different substrates. Both the first and second models are based on the generalized Babinet principle which can be applied to complementary electric disk and magnetic disk in the interface of different substrates. The former requires that only the magnetic disk should be dual, while the latter requires that both the substrates and the magnetic disk should be dual. After solving the fields of the dual electric disk (metallic cut-lines), the tangential transmission matrix of the complementary periodic metallic elements can be determined. When the incident angle is not very large, both the first and the second models are reliable. In order to realize the theoretical analysis at large incident angles, an effective substrate in the interface of the complementary metallic elements is introduced in the third model. As the thickness of the effective substrate approaches zero, a suitable boundary condition is provided for the periodic complementary metallic structures. The theoretical results are highly consistent with the simulation ones at arbitrary incident angle.
4）Study of the mechanism and application of gradient metasurface. Firstly, a refractive index gradient metasurface is constructed and confirmed to realize “anomalous reflection” and “surface wave coupling” through wave path difference in the substrate from the perspective of geometric optics. Then, the refractive index gradient metasurface is classified to be a special phase gradient metasurface, which is generally composed of the metallic resonant units with gradient reflective or transmissive phase distribution. After that, a three-band polarization-independent surface plasmon polariton coupler based on the phase gradient metasurface is designed and examined to bound to the surface. Finally, according to the reciprocity principle, the surface plasmon polariton coupler can also convert the surface wave into a plane wave through a suitable splitter feed. Thereby, a planar antenna with high gain and low profile at X band is designed based on the surface plasmon polariton coupler.
Translated Keyword
[Babinet principle, Four-dimensional characteristic matrix theory, Gradient metasurface, Metasurface, Polarization converter, Surface plasmon polariton planar antenna, Tangential network transmission theory]
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