A Well-Conditioned Non-Iterative Approach to Solution of the Inverse Problem

A novel methodology leading to well-conditioned formulation of the inverse scattering problem is proposed. The solution of the inverse scattering problem is made possible through elimination of the inherent ill-posedness of the inverse source problem. The latter is achieved by staging of the imaging experiment in a medium with the Green´s function exhibiting focusing properties. The method is shown to cast the inverse source problem into a well-conditioned matrix equation without addition of the non-physical regularization term to the pertinent integral equation. This is contrary to the conventional iterative optimization-like methods applied to regularized integral equation with non-directional Green´s function. The method is shown to be applicable in both traditional diffraction limited imaging where the evanescent waves do not participate in the information transfer from the object to the observation region as well as in the metamaterial media where focusing goes beyond the diffraction limit with the aid of the evanescent wave propagation. The diffraction limited imaging prototype is implemented using a parabolic reflector providing desired focusing properties of the Green´s function. The Raleigh criteria for diffraction limited resolution is revisited to demonstrate that upon availability of the medium providing sufficient focusing properties the resolution in the conventional diffraction limited microwave tomography can go up to half-wavelength. The implementation of algorithm in medium supporting evanescent wave propagation is demonstrated using the focusing Green´s function of the Veselago lens.