ABSTRACT
This chapter describes the development of a few negative refractive index (NRI) metamaterials with periodic structure whose unit cells are based on the concept of pairing two suitably shaped conductors, for microwave and optical frequencies. The presented metamaterial structures can be considered as generalizations of the short-wire or strip-pair design, which have been demonstrated to provide a magnetic response and negative permeability and to constitute an effective alternative to split ring resonators (SRRs). Materials based on coupled-particle arrangements with significantly different geometries may lead to negative index materials as well. The chapter investigates the properties at optical frequencies of certain plasmonic metamaterials whose constitutive unit cell generally consists of a cluster of metallic nanospheres. It shows that macroscopic effects in the response of these metamaterials are caused by the electromagnetic coupling between the metallic nanospheres closely packed in the metamaterial unit cell.
