Producing near-zero-index/directivity-tunable metamaterials using transformation optics
01 Dec 2021-Journal of The Optical Society of America B-optical Physics (Optical Society of America)-Vol. 38, Iss: 12, pp 3737-3742
TL;DR: In this article, a set of transformation mapping functions are introduced to produce near-zero-index metamaterials using non-transformation optics (TO) materials, which can be used in applications like radiators with highly tunable directivity.
Abstract: In some literature [Prog. Electromagn. Res.106, 107 (2010)PELREX1043-626X10.2528/PIER10060103], zero-index metamaterials are regarded as non-transformation optics (TO) materials. In this paper, for the first time, to the best of our knowledge, sets of transformation mapping functions are introduced to produce near-zero-index metamaterials using TO. In addition, other than producing near-zero materials, it is shown that the proposed structures can be used in applications like radiators with highly tunable directivity when the parameters of the transformation functions are adjusted. In near-zero-index metamaterials, the refractive index is near zero when either permittivity or permeability, or both, are near zero. The introduced mapping functions are applied to a desired space. Then, using Maxwell’s equations, the wave equation and consequently the wavenumber of the transformed space is obtained. From the wave equation the obtained wavenumber is near zero. Therefore, it is concluded that the transformed space is a near-zero-index material. The mapping is provided for open and enclosed spaces. At the end, a parametric numerical analysis is provided for various sets of obtained parameters for the introduced near-zero-index materials. From the analysis it is shown that the proposed structures can also be used as radiators with tunable directivity.
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