ABSTRACT
Gradient-refractive-index (GRIN) materials play an important role in inhomogeneous metamaterials. As we all know, the refractive index n = ϵ μ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315373614/16315673-39d0-4b15-8745-43c49a87259a/content/inline-math44.tif"/> . This means that the materials can be realized by tailoring their permittivity and/or permeability. In most cases, these materials are isotropic and nonmagnetic, that is, their electromagnetic (EM) parameters can be characterized by a scalar dielectric constant. However, as the technology evolves and more magnetic materials are involved in this area, GRIN materials employing inhomogeneous and magnetic materials can also be envisioned. In this chapter, however, we only focus on nonmagnetic materials.
