Prof. Ari Sihvola
Aalto University, Department of Radio Science and Engineering
Box 13000, FIN-00076 Aalto
Ari Sihvola was born in 1957, in Valkeala (Finland). He received the degrees of Diploma Engineer in 1981, Licentiate of Technology in 1984, and Doctor of Technology in 1987, all in Electrical Engineering, from the Helsinki University of Technology (TKK), Finland. Besides working for TKK and the Academy of Finland, he was visiting engineer in the Research Laboratory of Electronics of the Massachusetts Institute of Technology, Cambridge, in 1985–1986, and in 1990–1991, he worked as a visiting scientist at the Pennsylvania State University, State College. In 1996, he was visiting scientist at the Lund University, Sweden, and for the academic year 2000–2001 he was visiting professor at the Electromagnetics and Acoustics Laboratory of the Swiss Federal Institute of Technology, Lausanne.
In the summer of 2008, he was visiting professor at the University of Paris XI, France. Ari Sihvola is professor of electromagnetics in Aalto University School of Electrical Engineering (Aalto University was created in 2010 as a merger of three universities: Helsinki University of Technology, Helsinki School of Economics, and the University of Art and Design).
His scientific interests range from electromagnetic theory, complex media, materials modeling, remote sensing, and radar applications, into engineering education research and history engineering and technology. Ari Sihvola is Chairman of the Finnish National Committee of URSI (International Union of Radio Science), Vice Chairman of the Commission B (Fields and Waves) of the international URSI, and Fellow of IEEE. In 1990’s, he has served as Chairman of the IEEE AP–MTT Chapter for several years. He was awarded the five-year Finnish Academy Professor position in 2005–2010. He is also director of the Finnish Graduate School of Electronics, Telecommunications, and Automation (GETA). Author of several books and hundreds of publications, Ari has been active in organizing conferences and workshops, convening and chairing sessions, and serving in advisory, technical, and organizing committees for numerous national and international scientific symposia as member, secretary, or chairman. In TKK and Aalto University, Ari Sihvola has received several teaching awards, like the “Teacher of the Year” Prize in 1995 from the Student Union of TKK.
Characterization and Effective Description of Heterogeneous and Composite Electromagnetic Materials
In the analysis of electromagnetic fields interacting with material structures, the response of medium is condensed in dielectric and magnetic material parameters, like permittivity, conductivity, and permeability. In complicated and anisotropic media, these material parameters may need to be generalized from scalar quantities into matrices, or equivalently dyadics. The complicated response of materials is very often of structural origin, in other words the manner in which a heterogeneous mixture is formed determines its macroscopic electromagnetic material parameters. This lecture deals with the variety of ways how one is able to characterize and effectively describe the macroscopic dielectric and magnetic behavior of composite materials with given properties of the constituents and the geometrical microstructure. The rich history of homogenization of mixtures will be reviewed, including Clausius−Mossotti, Lorenz−Lorentz, Maxwell Garnett, Bruggeman, and other homogenization principles, and their ranges of applicability will be assessed. Mixing principles will be applied to mixtures that display very interesting properties that differ strongly from those of the constituent materials, like, for example, aqueous, strong-contrast, lossy, plasmonic, chiral, and bianisotropic mixtures.
Boundary Conditions and Extreme-Parameter Materials in Electromagnetics
In electromagnetics, the distinction between a boundary and an interface is fundamental. It is essential to emphasize the difference between these two concepts because very often in applied electromagnetics and in metamaterials studies, confusions exist. One often hears the question: “What is the material behind the surface on which a boundary condition is assumed?” The answer is, of course, that such a question is meaningless: nothing in the space on the other side of the boundary affects the fields in the domain of interest. On a boundary of a given spatial domain, electromagnetic fields have to be forced to satisfy a certain boundary condition in order to uniquely determine the field solutions. An interface problem is fundamentally different: the fields in the two domains have an interaction through tangential continuity conditions across the interface. The boundary–interface issue has a special significance in metamaterials studies where quite often the focus is on media with extreme constitutive parameters. Even if the boundary problem is different from the interface problem, they can be approximations or idealizations of each other. However, here it is important to keep clear what is the starting point and what is the approximation. Sometimes the interface problem is approximated by a boundary problem, which idealizes the situation and hence simplifies the analysis. The complementary procedure is a synthetic approach, where the boundary problem is primary and the question is how to construct and synthesize a real-world material structure that would best approximate the starting-point situation with the ideal boundary. In this lecture, I focus on this important distinction and show how well certain boundary conditions and complex surfaces can be simulated by material structures.
Philosophy of Metamaterials and Metasystems
Metamaterials have entered into the mainstream of electromagnetics, high-frequency engineering, and materials science research within a relatively short period. Even if the rapid progress in this field owes very much to earlier studies, it has managed to find a distinct profile and visibility within the first decade of the 21st century. Seminars, workshops, sessions, and even congresses dedicated to metamaterials are being organized, and the journal Metamaterials, published by Elsevier, runs already its sixth yearly volume (in 2012). Several books on the topic have appeared during the latest years. The potential for applications of metamaterials in the nanoscale, by manipulation of optical waves, has given rise to the field of metatronics. The prominence of metamaterials research wave is affecting the way electromagnetics problems and questions are approached even to the extent that one may talk about a metamaterials paradigm in research. The essential property in metamaterials is their unusual and desired qualities that appear due to their particular design and structure. These advantageous properties are not straightforward linear functions of the constituents from which the metamaterial is built up. A sample of metamaterial is more than a sum of its parts, analogously to the taste of ice-cream, which is not a direct sum of the flavors of ice and cream. Taking a more general perspective, we may observe that in the field of electromagnetic materials, there are several examples of media that fully deserve to be labeled metamaterials. Chiral (spatial-parity-breaking structures) materials, artificial magnetism, magnetoelectric materials, percolation processes, extremely anisotropic media, and other special media are complex enough to fall in the category of metamaterials. This lecture discusses fundamental issues associated with metamaterials, like possibilities to find a unique definition for them, the spatial scales and geometrical constellations for which one can talk meaningfully about metamaterials, and meta-type characterization of engineering structures and systems in general.