Design and Characterization of Functional Structures for Electromagnetic Waves

Abstract: This dissertation deals with design and characterization of functional structures for scattering of electromagnetic waves. An abundance of these structures can be found in nature, such as the structural coloration in the feathers of a peacock, the scales of butterflies and the shell of scarab beetles. Human design of structures providing specific interactions with electromagnetic waves have a long history. Today, these structures can be found in everyday products and applications like the filter of a microwave oven, shaded windows, polarizing glasses and 3D movies. A high demand of functional structures is also found in more advanced applications such as antenna design, electromagnetic scattering reduction for stealth applications, and in satellite communication systems.The dissertation consists of a general introduction and nine scientific papers, of which the majority have been published in peer-reviewed international journals. The general introduction sets the stage for the technical details contained in the included papers. Fundamental relations and scattering concepts in electromagnetic theory are presented, alongside with the approaches for design, optimization and experimental characterization of functional structures. The included papers can be divided into two main tracks: Papers I–VI concern satellite communications and Papers VII–IX are related to electromagnetic scattering characterization and reduction.In Papers I–V circular polarization selective structures for satellite communication applications are designed and characterized numerically and experimentally. A novel concept design is presented providing more than double the frequency bandwidth of previous designs. Furthermore, an experimental procedure and a data post processing scheme are presented for accurate characterization of circular polarization selective structures. In Paper VI a multiphysics study of a triaxial weave functioning as a reflector antenna surface is presented. The electromagnetic scattering properties of the structure are evaluated using numerical simulations and approximation models. These results are combined with an acoustic study and design guidelines for such space antennas are specified.In Papers VII–VIII electromagnetic radiation-absorbing materials for scattering reduction applications are evaluated. By using an analytic framework in canonical scattering problems, and numerical methods in more application oriented scenarios, two fast computation methods are developed. These methods are used to evaluate a number of different radiation-absorbing materials in different scenarios, and provide information of the physical interaction between electromagnetic waves and scatterers coated with said materials. Finally, in Paper IX different methods are utilized to locate defects in composite materials. Compressive sensing techniques are implemented to achieve sub-wavelength resolution of data extracted from experimentally acquired scattered fields. A key point is identifying that the scattering from hidden defects can be formulated as a sparse inverse scattering problem in some basis.