3-Dimensional Iterative Forward Model for Microwave Imaging

The efficient solution of a forward scattering problem is the key point in nonlinear inversion schemes associated with microwave imaging. In this paper the solution is presented for the volume integral equation based on the method of moments (MoM) and accelerated with the adaptive integral method (AIM). The proposed technique differs from the usual well-known MoM and AIM in the way the matrices are computed and stored. It is shown that the MoM matrix can be split in parts, which are independent of the material parameters of the scattering object. Then, provided with the actual values of the object parameters, the matrix is promptly restored in each iteration of the nonlinear inversion process. The coefficients of the multipole expansion of the basis functions in AIM are also computed irrespective of the object properties, so that the far-field contribution is computed on-the-fly via FFT in each iteration of the forward solution. Thus, the presented technique allows us to avoid the time-consuming procedure of the MoM matrix filling in each inversion iteration. Furthermore, the forward solution from the previous inversion iteration can be utilized in the next one as an initial guess, thus reducing the solution time for the forward model.