Metamaterials—artificially structured microcircuits that can mimic the electromagnetic response of atoms and molecules—have vastly expanded the opportunities available for the design of electromagnetic structures. Starting in 2000 with the first report of a “left-handed” metamaterial, for which both the electric permittivity and magnetic permeability are simultaneously less than zero, metamaterials have been demonstrated to exhibit properties either difficult to achieve or non-existent in conventional materials. The left-handed metamaterial was a particularly striking example because it had been theorized as possible in 1968 by Russian physicist Victor Veselago, but had never been demonstrated before.
Over the past eight years, our understanding of metamaterials has enabled us to make progressively more sophisticated media, from simple optics to gradient optics, and most recently transformation optics. Transformation optical structures require the full flexibility offered by metamaterials, because these designs require simultaneous and independent gradients in the elements of the permittivity and permeability tensors. If the rather severe constitutive parameter requirements can be realized, entirely new types of devices can be designed by the transformation optical approach, including “invisibility cloaks” that can enable an object to be concealed over a finite electromagnetic band of frequencies. Like the first negative index metamaterial, the transformation optical cloak reveals what is possible as we start exercising the electromagnetic degrees of freedom offered us by metamaterials.
Dr. David R. Smith is currently the William Bevan Professor of Electrical and Computer Engineering Department at Duke University and Director of the Center for Metamaterial and Integrated Plasmonics. He also holds the positions of Adjunct Associate Professor in the Physics Department at the University of California, San Diego, and Visiting Professor of Physics at Imperial College, London. Dr. Smith received his Ph.D. in 1994 in Physics from the University of California, San Diego (UCSD). Dr. Smith’s research interests include the theory, simulation and characterization of unique electromagnetic structures, including photonic crystals and metamaterials. Dr. Smith is best known for his theoretical and experimental work on electromagnetic metamaterials. Metamaterials are artificially structured materials, whose electromagnetic properties can be tailored and tuned in ways not easily accomplished with conventional materials. Smith has been at the forefront in the development of numerical methods to design and characterize metamaterials, and has also provided many of the key experiments that have helped to illustrate the potential that metamaterials offer. Dr. Smith and his colleagues at UCSD demonstrated the first left-handed (or negative index) metamaterial at microwave frequencies in 2000--a material that had been predicted theoretically more than thirty years prior by Russian physicist Victor Veselago. No naturally occurring material or compound with a negative index-of-refraction had ever been reported until this experiment. In 2001, Smith and colleagues followed up with a second experiment confirming one of Veselago's key conjectures: the 'reversal' of Snell's law. These two papers--the first published in Physical Review Letters and the second in Science--generated enormous interest throughout the community in the possibility of metamaterials to extend and augment the properties of conventional materials. Both papers have now been cited nearly 2,000 times each.
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