Detection at microwave frequencies based on self-adjoint sensitivity analysis

A novel general formulation of the response sensitivity analysis is proposed and implemented in a computationally efficient algorithm for the detection of electrically small scatterers in a known background medium. The responses of the background medium where no scatterers are present are modeled via ultra-wideband time-domain simulation. Using these modeled responses and the measured responses of the examined object, 3D derivative maps are obtained within the object's volume. The minima or maxima in these maps indicate the locations where the voxel permittivities and conductivities differ significantly between the measured and modeled media. Localization of the scatterers in a complex heterogeneous example is successfully conducted. The limitations of the detection algorithm and its resolution are studied using a homogeneous background example in terms of the number of transmission/reception points, the dielectric contrast and the size of the scatterer.