Over the past decade, intense research into the properties of engineered, artificial materials has shown that remarkable effective material properties can be realized by controlling the geometry of sub-wavelength, metallic circuits. Metamaterials have been demonstrated that support material properties that do not appear in naturally occurring materials. The negative index medium that precipitated the field a decade ago provided an early and compelling example. Leveraging the control over material parameters now available, we can design new devices based on precisely patterned spatial gradients in the anisotropic tensor components of an effective medium. The “invisibility cloak,” demonstrated by our group at Duke in 2006, is just such a possibility, though there are many others.
As remarkable as their passive material properties are, metallic metamaterials also have the capability to provide new classes of active, tunable and nonlinear media. Because the electromagnetic fields are strongly enhanced within the capacitive regions of metallic, resonant metamaterials, it is possible to hybridize the response of conventional materials introduced into the high field regions of metamaterial composites with the engineered, passive properties of the host metamaterial. Hybrid metamaterials are good candidates for applications at infrared and visible wavelengths, since they can perform a useful operation on incoming light—such as wave mixing, modulation, tuning or harmonic generation—within a minimal propagation length.
Metamaterials are naturally described using the physics-based language of effective medium theory and electrodynamics. The materials description of metamaterials is complementary to that of the engineering description, which can usually be applied with equivalent results; the advantage of either description is most likely related to the particular design under consideration. As metamaterials are now transitioning into a variety of application spaces, including radar, antennas and communications, the interdisciplinary mix of the material and engineering descriptions is becoming routine.
In this talk, I will describe several nearer term potential applications of metamaterials, and will discuss ongoing efforts and opportunities at Intellectual Ventures to take the next steps towards metamaterials commercialization.
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.<p
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.