Metasurfaces for general transformations of electromagnetic fields
Professor Sergei Tretyakov, Aalto University, Finland
Abstract
Electromagnetic fields can be controlled and transformed using engineered materials, often called metamaterials. The conventional paradigm of using metamaterials for transformations of electromagnetic fields implies that we engineer artificial materials in such a way that the polarization and conduction currents induced in the material, acting as secondary sources, create the desired fields outside or inside of the metamaterial sample. Huygens’ principle tells, however, that the same fields outside of the sample volume can be found as those generated by equivalent surface currents flowing only on the volume surface. Thus, it appears that the same field transformations can be achieved by engineering only surface currents of the volume surface, and there appears to be no reason why the volume enclosed by such an “engineered surface” could not be made negligibly small. In this review talk we will discuss electrically (optically) thin composite sheets with engineered and optimized properties: metasurfaces for general transformations of electromagnetic fields. The main motivation is a possibility to realize quite general functionalities (absorption, polarization transformations, control over reflection phase, focusing, etc.) using just single arrays of electrically small engineered particles. In this talk we will explain what physical properties of metasurface unit cells are responsible for various field transformations, provide basic design equations, and illustrate the potentials of this technology by several examples from our experimental work.
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Professor Sergei Tretyakov, Aalto University, Finland
Professor Sergei Tretyakov, Aalto University, Finland
Professor Sergei A. Tretyakov (Fellow, IEEE) received his Dipl. Engineer-Physicist, the Candidate of Sciences (PhD), and Doctor of Sciences degrees (all in radiophysics) from the St. Petersburg State Technical University, Russia, in 1980, 1987, and 1995, respectively. From 1980 to 2000 he was with the Radiophysics Department of the St. Petersburg State Technical University. From 2000 he has been working in Helsinki University of Technology, Finland, which became Aalto University in 2010, after a merge with two other universities in Helsinki. Presently, he is professor of radio engineering at the Department of Radio Science and Engineering, Aalto University, Finland. The main scientific interests of Professor S. Tretyakov are electromagnetic field theory, complex media electromagnetics, antennas, and microwave engineering. He is the author or co-author of four research monographs, 16 book chapters, and more than 240 journal papers.
Metasurface Transformation Electromagnetics
Professor Stefano Maci, University of Sienna, Italy
Abstract
Metasurfaces constitute a class of thin metamaterials, able to support surface wave propagation. At microwave frequencies, they are constituted by sub-wavelength size patches printed on thin grounded or ungrounded dielectric substrates. By averaging the tangential fields, the metasurfaces may be characterized by homogenised isotropic or anisotropic boundary conditions, which can be approximated through a homogeneous equivalent impedance. In absence of losses, this impedance supports a surface-wave propagation. The impedance can be spatially modulated by locally changing the sizes/orientation of the local printed element. This allows for a deformation of the wavefront which addresses the local wavector along not-rectilinear paths. In fact, the modulated anisotropic impedance imposes a local modification of the dispersion equation and, at constant operating frequency, of the local wavevector. The effect of the metasurface-modulation can be analized in the framework of Transformation Optics This talk reviews theory and implementation of metasurface transformation optics in microwave devices.
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Professor Stefano Maci, University of Sienna, Italy
Professor Stefano Maci, University of Sienna, Italy
Stefano Maci is a Professor at the University of Siena (UNISI) and Director of the PhD School of Information Engineering and Science, which presently includes about 60 PhD students. Since 2000, he has been P.I. of 10 research projects funded by the European Union (EU) and by the European Space Agency (ESA). In 2004 he founded the European School of Antennas (ESoA), a PhD school that presently comprises 35 courses on Antennas, Propagation, and Electromagnetic Theory. He is presently Director of ESoA, a member of the Delegate Assembly of EurAAP (European Association of Antennas and Propagation), a member of the TAB (Technical Advisory Board) of the URSI Commission B, Chair of the Award Committee of the IEEE Antennas and Propagation Society (US), a member of the AP Executive Board of IET (UK), a Distinguish Lecturer of IEEE. He was recipient of several awards, among which the EurAAP Carrier Award 2014. He is author of 130 papers published in international journals, 10 book chapters, and about 300 papers in proceedings of international conferences.
A new look at transformation electromagnetics approach for designing electromagnetic devices such as flat lenses, reflectarrays and blankets for radar cross section reduction of real-world objects
Professor Raj Mittra, Pennsylvania State University, USA
Abstract
In this paper we present an alternative approach to addressing the problem of designing a number of practical “microwave” devices such as: blankets serving as absorbers for radar targets; flat lenses; and reflectarrays. Recently, these design problems been dealt with by a number of researchers using the transformation optics (TO) algorithm, which is based upon transforming the geometry of an object from real space to virtual space while keeping the Maxwell’s field solutions from real space to virtual space intact. The TO algorithm typically leads to designs that call for anisotropic values in real space in order to preserve the field variations as we navigate from the real space to virtual space and vice versa. In contrast to the TO, the proposed algorithm is based on “Field Transformation (FT),” as opposed to geometry transformation. The FT algorithm has been designed to transform the electromagnetic field distribution in an input aperture, generated by a given source distribution, to a desired distribution in the exit aperture. We show how we can cast the design problem into a Scattering Matrix approach, wherein the case of RCS reduction problem the design is based on controlling only the Magnitude of S11, whereas for the Lens or Reflectarray problems, we specify only the desired Phase of S12 without being concerned about its magnitude. In contrast to this, the TO imposes strict conditions on both the magnitude and phase characteristics of S11 and S12, which in turn calls for anisotropic metamaterials. The Scattering Matrix/Field Transformation approach avoids these problems altogether and is able to work with only materials for the lens and reflectarray problems, and with realizable complex (materials that have wideband characteristics and do not suffer from the shortcomings of the MTMs.
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Professor Raj Mittra, Pennsylvania State University, USA
Professor Raj Mittra, Pennsylvania State University, USA
Raj Mittra is a Professor in the Electrical Engineering department of the Pennsylvania State University, where he is the Director of the Electromagnetic Communication Laboratory. Prior to joining Penn State he was a Professor in the Electrical and Computer Engineering at the University of Illinois in Urbana Champaign from 1957 through 1996, when he moved to his present position at the Penn State University. Currently, he is also a Professor at the University of Central Florida in Orlando, FL.He is a Life Fellow of the IEEE, a Past-President of AP-S, and he has served as the Editor of the Transactions of the Antennas and Propagation Society. He won the Guggenheim Fellowship Award in 1965, the IEEE Centennial Medal in 1984, and the IEEE Millennium medal in 2000. Other honors include the IEEE/AP-S Distinguished Achievement Award in 2002, the Chen-To Tai Education Award in 2004, the IEEE Electromagnetics Award in 2006, and the IEEE James H. Mulligan Award in 2011. He has been a Visiting Professor at Oxford University, Oxford, England and at the Technical University of Denmark, Lyngby, Denmark.
Spatial transformation enabled electromagnetic devices: From radio frequencies to optical wavelengths
Professor Douglas Werner, Pennsylvania State University, USA
Abstract
Transformation optics provides scientists and engineers with a powerful new design paradigm to tailor the material properties of a medium (i.e., the spatial distribution and/or anisotropy), thereby allowing for comprehensive manipulation of electromagnetic waves with unprecedented flexibility. Based on such a mathematical framework, various interesting electromagnetic wave phenomena have been revealed over the last decade and employed to develop a wide range of novel devices that target applications throughout the electromagnetic spectrum. This presentation will focus on both theoretical and experimental investigations into the design of transformation optics enabled devices for shaping or controlling electromagnetic waves (radiation and scattering), at radio frequencies as well as optical wavelengths. Several types of coordinate mappings, which are variations based on the originally proposed transformation optics design methodology, are exploited for different applications to provide expanded design flexibility, enhanced device performance, and reduced implementation complexity. These include the complex coordinate transformation for simultaneous amplitude and phase control, linear coordinate transformations for broadband operation, conformal mappings with electrically tunable transformed space geometry for microwave antenna systems, and quasi-conformal mappings for optical applications. The illustrated design examples will serve to demonstrate the comprehensive capability of transformation optics in controlling electromagnetic waves, while the associated devices will open up new pathways toward future synthesis and design of integrated electromagnetic components, ranging from the microwave to optical spectral regimes.
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Professor Douglas Werner, Pennsylvania State University, USA
Professor Douglas Werner, Pennsylvania State University, USA
Douglas H. Werner holds the John L. and Genevieve H. McCain Chair Professorship in the Pennsylvania State University Department of Electrical Engineering. He is the director of the Computational Electromagnetics and Antennas Research Lab (CEARL) as well as a faculty member of the Penn State Materials Research Institute (MRI). He has received numerous awards including the inaugural IEEE Antennas and Propagation Society Edward E. Altshuler Prize Paper Award and the Harold A. Wheeler Applications Prize Paper Award in 2011 and 2014 respectively. Prof. Werner has published over 600 technical papers and proceedings articles. He has also published several books including Genetic Algorithms in Electromagnetics (Hoboken, NJ: Wiley/IEEE, 2007) and Transformation Electromagnetics and Metamaterials: Fundamental Principles and Applications (London, UK: Springer, 2014). He is a Fellow of the IEEE, the IET, and the ACES.