Colloquium
February 4, 2004

Dr. Vasundara V. Varadan
George & Boyce Billingsley Chair and Distinguished Professor
Department of Electrical Engineering, University of Arkansas

Negative Permittivity, Permeability and Refractive Index in Ordered and Random Metamaterials

The concept of negative index materials (NIM) postulated by Veselago (1967) have commanded intense interest after recent experimental demonstration of negative refraction by engineered structures. NIM are intriguing not only for the potential applications to super lenses and near field focusing but also because the physics of NIM appear counter intuitive. This talk will overview the field and discuss interesting experimental results that have lead to direct negative index measurements (both negative permittivity and permeability) at MW frequencies. Experimental results showing negative permittivity, permeability and refractive index are presented for ordered and random metamaterials that exhibit plasmonic resonances at the frequency range of interest. Measurements are made using a pair of horn antennas with dielectric lenses that illuminate planar samples with focused plane waves. Several different types of scattering elements were used to make the samples, such as – left, right and racemic mixtures of small metallic springs, metallic Omega shaped elements, combinations of split ring resonators and wire elements. It is shown that it is possible for all such scatterers to exhibit negative refraction. It is believed that this may be the first time that negative dielectric and magnetic properties have been measured experimentally. It is shown that disordered structures can also lead to NIM behavior thus periodicity is not required. Nonreciprocal behavior in pseudochiral media exhibiting NIM behavior is examined. Homogenization methods that are used by experimentalists and theorists alike to derive effective medium properties are discussed with reference to NIM. Finally, challenge in realizing near term applications with engineered NIM will be discussed.