Synthesis of innovative electromagnetic devices via inverse scattering techniques

This Thesis deals with the synthesis of innovative microwave devices via inverse scattering based theoretical tools and actual procedures. The electromagnetic scattering phenomenon occurs when the presence of an inhomogeneity in the space originates a perturbation of the field which is propagating. In the considered region of space, a new electromagnetic field occurs and such a total field is nothing but a superposition of the original one and the perturbation caused by the obstacle (or scatterer), which is called “scattered field”. The usual aim of an inverse scattering problem is to retrieve the location, the shape and the electromagnetic parameters of the scatterer by processing measurements of the scattered field. Several difficulties come into play in solving such a diagnosis problem, since the non linearity and the ill-posedness of the problem must be faced. Therefore, efficient solution strategies and regularization techniques have to be exploited to reach accurate and meaningful solutions. Interestingly, the inverse scattering problem can be turned into a synthesis problem, provided the starting data is no longer a collection of measurements but rather some field specifications arising from design constraints. In the Thesis, some methodologies already available in the inverse scattering community for diagnosis applications are extended and modified for design purposes. Theoretical results include a new representation for non radiating sources and spectral analysis of some scattering approximations which are both of interest for design of invisibility devices. Methodological results include two new effective solution procedures for the general inverse scattering problem. Moreover, a well known inversion procedure is considerably modified and extended in order to include the synthesis of the excitations of some primary sources. Last, but not least, a new procedure is proposed for the synthesis of Artificial Materials based devices which outperforms a more intuitive homogenization based method. Finally, the developed approaches and procedures are validated through the synthesis of an optimal monopulse antennas as well as of new invisibility cloaks.