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All-angle broadband ENZ metamaterials

A novel type of metamaterial is presented to produce broadband near-zero effective permittivity to a defined polarized probing electromagnetic wave with varying angles of incidence. The metamaterial has a uniaxial unit cell structure made up of symmetric periodic multilayer superlattices with a rotational symmetry about the polarization of the probing electromagnetic wave. The unit cell is rigorously constructed based on the Bergman–Milton spectral representation of the effective permittivity, and its electrodynamic properties are theoretically verified by the eigenmode analysis, the band structure, the dispersion relation, and the isofrequency contours. The eigenmode analysis illustrates that the unit cell can be effectively regarded as a photonic crystal or a waveguide according to the incidence direction of the probing electromagnetic wave, and either of them is of the dynamic microstructure related to the frequency, which results in a broadband response. Meanwhile, the band structure, the dispersion relation, and the isofrequency contours show that the unit cell has the near-zero effective permittivity at all angles of incidence of the specified polarized probing electromagnetic wave. Finally, the reflection/transmission/absorption spectra to the prescribed polarization probing electromagnetic wave vividly reveal the all-angle broadband near-zero effective permittivity property of the metamaterial.