The Power of Metamaterials: From Negative Refraction to Invisibility Cloaks

In 2000, our group (then at UCSD) presented the first experimental demonstration of a negative index medium [1-4]. The existence of such a material had been postulated decades earlier by Russian physicist Victor Veselago [5], yet a material with a negative index had never been found or synthesized using conventional materials. However, from an electromagnetic point-of-view, what constitutes a medium actually provides an enormous amount of flexibility, so that new materials can be created by combining macroscopic (but subwavelength) elements into a composite. In this way, artificial materials—or metamaterials—can be constructed that have electromagnetic properties beyond those that can be found in naturally occurring materials. Negative index metamaterials, in which both the electric permittivity and the magnetic permeability are negative, represent one very interesting example. But negative index materials are just the beginning of the unique structures that are possible: metamaterials with spatial gradients in the permittivity and/or permeability tensors have also been developed and have shown potential as lenses and similar devices [6, 7]. More recently, we and others have shown that a new class of electromagnetic devices—closely related to gradient index metamaterials—can be designed by applying coordinate transformations to Maxwell’s equations. In particular, we have determined the necessary transformation that proscribes the material parameters for an invisibility cloak [8, 9]. The cloak represents just one compelling example of the structures that can be designed via transformation optics [8, 9]. The structures that result from the transformation optics approach are inherently anisotropic and exhibit very complicated spatial gradients in all of the constitutive tensor elements. Yet, we believe that even these complex structures should be realizable, at least in some frequency bands and in some approximation, by the use of metamaterials.
David Smith earned his Ph.D. in Physics from the University of California at San Diego, and then worked as a postdoc researcher on plasmon resonant particles as optical labels for biological and biochemical assays. Smith's research interests include photonic crystals, metamaterials and negative index media, plasmon nanophotonics, and self-monitoring composites. Smith's research, featured in the June 2004 issue of Physics Today, demonstrated that materials engineered to have negative permittivity and permeability demonstrate exotic behavior such as negative refractive index to subwavelength focusing.
Research Interests: Photonic crystals; Metamaterials and negative index media; Plasmon nanophotonics; Self-monitory composites.