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Hyperbolic metamaterial (HMM) research has led to the fabrication of devices which have unbounded k-space ellipsoids. Alternating layers of films with alternating signs of relative permittivity or permeability in a given direction enable multi-layer surfaces that are, in theory, either perfectly reflective or transmissive at an angle dependent upon the free space wave vector and ratios of the permittivity or permeability in the normal and transverse directions. By having knowledge of the electromagnetic properties of the constituent materials of a multi-layer HMM over a given bandwidth, the functionality of these structures can be altered by changing the fill fraction of the constituents. One potential device design that results is that of a flat electromagnetic wave collimator. The degree to which a multi-layer HMM collimates comes from the contrast in the magnitudes of the relative permeability or permittivity in the normal and transverse directions. With a large material parameter contrast at a given frequency, the number of transverse wave vectors that allow for successful EM wave propagation at the HMM/atmosphere interface approaches zero. This leads to propagation of a narrow angular cone of waves relative to the surface normal of the HMM. Herein we show that analytical calculations are in relatively good agreement with finite element method electromagnetic simulations performed in COMSOL’s RF module and compare dispersion relations of known materials to the resulting collimation generated in a corresponding HMM. We thereby use existing material data and predictive theories show how to tailor the frequency response of HMMs.
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Daniel B. Fullager, Michael A. Fiddy, "Design theory of thin film hyperbolic metamaterial colimators," Proc. SPIE 9544, Metamaterials, Metadevices, and Metasystems 2015, 95441T (1 September 2015); https://doi.org/10.1117/12.2187690