In this Letter, experimental realization of recently proposed DB metasurface is presented. A compact DB unit cell is proposed and its operating principle is tested both numerically and experimentally. Practical realization of a single layer DB metasurface, composed of 16 DB unit cells, is presented. Prototyped DB metasurface was measured in a waveguide environment and obtained experimental results support theoretically predicted DB properties.
To date, research on metasurfaces has predominantly focused on those with polarizabilities that are tangent to the metasurface. A few theoretical works have characterized metasurfaces with normal polarizabilities. In fact, experimental extraction of the surface polarizabilities of such metasurfaces has not been reported to date. Here, we provide full analytical, numerical, and experimental characterizations of a metasurface that can be described with polarizabilities in all three spatial directions. First, a set of equations is derived that allows a surface distribution of scatterers to be replaced by a sheet boundary condition. It is shown that the extraction of unknown polarizabilities in the normal direction necessarily requires scattering parameters obtained from oblique incidence. Closed-form expressions that relate scattering parameters to surface susceptibilities in all three spatial directions are given. It is shown that the reflection and transmission properties of the metasurface can be predicted, for an arbitrary angle of incidence, from the sheet parameters. In addition, we report the experimental characterization of a metasurface with polarizabilities in the normal direction. The free-space measurements were performed on a recently proposed DB surface at 10 GHz. Experiments confirmed that the sheet parameters do not change with angle of incidence. Consequently, it was possible to extract surface susceptibilities in the normal direction from measured transmission parameters alone. PACS numbers: 81.05.Xj, 41.20.Jb st sz s st sz J J J z j z j z
A counter-intuitive phenomenon of propagation below cut-off in a waveguide filled with an anisotropic mu-negative metamaterial is investigated analytically, numerically, and experimentally. It is shown that the equivalent plane waves that make up the waveguide mode are inhomogeneous, and this fact is responsible for subwavelength guiding of electromagnetic energy. It was also found that the microscopic ('in-cell') magnetic field distribution in a waveguide filled with split-ring resonators may significantly differ from the distribution in the homogenized waveguide. However, spatial averaging of a numerically calculated magnetic field across the unit cell yielded a distribution that was very similar to the distribution in the continuous mu-negative material. Experimental waveguides filled with split-ring resonators were prototyped in the 8-GHz band, and measurement results were found to be in good agreement with all analytical and numerical predictions. This shows that it is indeed possible to interpret the waveguide filled with split-ring resonators as a homogenized waveguide filled with a continuous anisotropic mu-negative metamaterial.
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