Retrieval of Composite Model Parameters for 3-D Microwave Imaging of Biaxial Objects by BCGS-FFT and PSO

This article presents the 3-D quantitative microwave imaging of homogeneous biaxial anisotropic objects with their optical axes being in arbitrary directions. Two sets of model parameters, the anisotropic dielectric parameters and the angles of optical axes with respect to the user-defined coordinate system, are retrieved iteratively. In the forward model, the total fields are solved from the discretized combined field volume integral equations (CFVIEs) by the stabilized biconjugate gradient fast Fourier transform (BCGS-FFT) method. In the inversion model, the optimized solutions for two sets of model parameters are obtained by the particle swarm optimization (PSO) method. If the geometric models of the homogeneous anisotropic objects are unknown, a full-wave inversion method, the variational Born iterative method (VBIM), is combined with the multiparametric structural consistency constraint (SCC) to find the spatial boundaries of the homogeneous objects in advance. Two numerical examples are used to test the proposed method, and the results show that BCGS-FFT-PSO not only has strong adaptability for optical axes angles varying in wide ranges but also can retrieve composite model parameters of multiple homogeneous biaxial objects simultaneously even when the measured data are contaminated by noise.