About the Event
Recently a new generation of structures has been proposed that do not scatter electromagnetic field i.e. that can cloak a certain object. A practical realization of such cloaks requires materials that are not found in nature, but which can be synthesized using metamaterial approach. Experimental demonstration (Schurig, et al.) opened a large discussion about limitations of the proposed structures in terms of losses, dispersion and sensitivity to the incidence angle.
The focus of this presentation is to show the results of a detailed analysis of uniaxial multilayer cylinders used for invisible cloak realization and to also highlight some directions for future designs. The analysis approach is based on the modal approach, i.e. the radial field distribution is described with a modified Bessel differential equation that takes into account the radial anisotropy of the proposed structures. For the oblique incidence case we have developed more general analysis approach in which distribution of the electromagnetic field in radial direction is determined using finite-difference discretization of the appropriate partial differential equations. This analysis was also expanded in order to model dispersion effects, and finally for the purposes of optimization a PSO algorithm was implemented. With this we have developed a software platform that can be used to rigorously characterize cylindrical cloaks, provide us with an insight on actual problems and show how to simplify and improve some characteristics.
The second part of presentation will discuss the analysis of conformal antennas. Starting from the basic principles of Green’s functions and spectral domain approach, the idea was to modify the analysis method in order to make it computationally more efficient (and by this to create suitable tools for the first stage of the design process). This concept was applied in the analysis of various conformal antennas and periodic structures. For example, a novel hybrid method for the analysis of electrically large conformal antennas (containing microstrip or waveguide radiating elements and multilayered dielectric coating) named Spectral Domain – Uniform Theory of Diffraction (SD - UTD) was developed. It combines the advantages of the spectral domain approach - the ability to study multilayer canonical structures - and of the UTD method - the ability to analyze general curved structures. The same idea was extended to enable the analysis of curved periodic structures. Complexity and needed computation time of the moment method analysis approach is additionally reduced by applying particular series acceleration techniques to the partial sums encountered in these problems. The Wynn’s ε-acceleration technique is investigated and modified in order to achieve better convergence. The results show excellent convergence properties when applying this method to the analysis of antennas printed on cylindrical and spherical substrates.
Zvonimir Sipus was born in Zagreb, Croatia, in 1964. He received the B.Sc. and M.Sc. degrees in electrical engineering from the University of Zagreb, Croatia, in 1988 and 1991, respectively, and the Ph.D. degree in electrical engineering from Chalmers University of Technology, Gothenburg, Sweden, in 1997. From 1988 to 1994, he worked at Rudjer Boskovic Institute, Zagreb, Croatia, as Research Assistant, involved in the development of detectors for explosive gases. In 1994, he joined the Antenna Group at Chalmers University of Technology, where he was involved in research projects concerning conformal antennas and soft and hard surfaces. In 1997 he joined the Faculty of Electrical Engineering and Computing, University of Zagreb, where he is now a Professor. Since 2008 he is the Head of the Department of Wireless Communications there. From 1999-2005 he was also an adjunct researcher at the Department of Electromagnetics, Chalmers University of Technology. His main research interests include numerical electromagnetics with application to antennas, microwaves, and optical communications.