Abstract
Over the past several years, the concept of transformation optics has emerged as a new method of designing
complex electromagnetic structures and devices. In the transformation optics approach, the behavior of a wave is
modified by conceptually warping the space through which it propagates. The wave, fixed to its original
coordinate frame, is thereby modified in accordance with the transformation. With the desired design found, the
optimized coordinate transformation can then be introduced in Maxwell’s equations and used to renormalize the
constitutive material parameters.
Transformation optics is an intuitive approach to electromagnetic design that has already produced compelling
new opportunities. The recently reported “invisibility cloak” is an example of the unique classes of structures
now available with this unique design approach. However, these new opportunities come at a significant cost.
The materials generally specified by the transformation optical approach are typically extremely complex,
requiring independent spatial gradients in all of the constitutive tensor elements. Such materials would be
difficult if not impossible to achieve in any practical sense. Yet, recent developments in artificially
structured materials—or metamaterials-have provided us with a path to the realization of transformation optical
media.
Because there are an infinite set of transformations that will accomplish the identical functionality, there are
huge opportunities for optimizing and tuning the design to more easily facilitate realization by metamaterials.
Fabrication and material constraints can be fed back into the design procedure, resulting in the greater
likelihood of practical structures. Using a variety of optimization approaches, the first transformation optical
"cloaks" were, in fact, demonstrated this year by two groups at wavelengths near 1.5 microns. These experiments
indicate that there are bright prospects for achieving remarkable transformation optical structures at IR and
visible wavelengths.
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| Biography of
David R. Smith
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.
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.
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.
Since those first metamaterial experiments, Smith has continued to study the fundamentals and potential
applications of negative index media and metamaterials. In 2004, Smith began studying the potential of
metamaterials as a means to produce novel gradient index media. By varying the index-of-refraction throughout a
material, an entire class of optical elements (such as lenses) can be formed. Smith showed that metamaterials
could access a much larger range of design space, since both the magnetic and the electric properties could be
graded independently. Smith and colleagues demonstrated several versions of gradient index optics, an activity
that continues in his lab today.
The introduction of controlled spatial gradients in the electromagnetic properties of a metamaterial flows
naturally into the broad concept of transformation optics—a new electromagnetic design approach proposed by Sir
John Pendry in 2006. To illustrate of the novelty of this design approach, Pendry, Schurig and Smith suggested
in 2006 that an 'invisibility cloak' could be realized by a metamaterial implementation of a transformation
optical design. Later that same year, Smith’s group at Duke University reported the demonstration of a
transformation optical designed “invisibility cloak” at microwave frequencies. The concept of transformation
optics has since attracted the attention of the scientific community, and is now a rapidly emerging
sub-discipline in the field. Smith's work on transformation optics has been featured in nearly every major
newspaper, including a cover story in USA Today, The New York Times, The Chicago Tribune, The Wall Street
Journal, The Washington Post and many more. Smith and his work on cloaking have also been featured on television
news programs inlcuding The Today Show, Countdown with Keith Olbermann, Fox News, CNN and MSNBC. Smith's work
has also been highlighted in documentary programs on The History Channel, The Discovery Channel, The Science
Channel, the BBC and others.
In 2002, Smith was elected a member of The Electromagnetics Academy. In 2005, Smith was part of a five member
team that received the Descartes Research Prize, awarded by the European Union, for their contributions to
metamaterials and other novel electromagnetic materials. Smith also received in 2005 the Stansell Research Award
from the Pratt School of Engineering at Duke University. In 2006, Dr. Smith was selected as one of the
“Scientific American 50,” a group recognized by the editors of Scientific American for achievements in science,
technology and policy. In 2008, Smith received a numbered coin from DARPA DSO (Defense Sciences Office) for his
metamaterial contributions. He also took part as a panelist in a Congressional Briefing that year, "Basic
Research Drives Defense Technologies." Dr. Smith’s work has twice appeared on the cover of Physics Today, and
twice been selected as one of the “Top Ten Breakthroughs” of the year by Science Magazine. Smith has more than
twenty patent disclosures, with four issued patents relating to plasmonics and metamaterials.
This website is maintained by Yongyi Mao, and was last
updated on Sept 12, 2009
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