Simulation-based microwave imaging of plain and reinforced concrete for nondestructive evaluation

Abstract

The focus of this paper is the implementation of a backpropagation algorithm as a potential solution for the inverse source problem for microwave imaging of plain and reinforced concrete targets. The data used in imaging was obtained from numerical simulation of far-field microwave scattering by concrete targets using typical frequency bandwidth of commercially available radar systems. A finite difference-time domain (FD-TD) technique was used for the simulations. Electromagnetic (EM) properties of concrete for various moisture conditions were obtained from a previous study. A total of four simulations were performed using a Gaussian pulse wave excitation for dry and moisture saturated concrete cylinders with and without a rebar at the center. The reflected and transmitted fields were recorded along two measurement lines. Images reconstructed using the backpropagation algorithm showed the potential of the method for concrete non destructive testing (NDT) while drawing attention to its limitations mainly due to the linearizing assumptions made in the algorithm’s formulation. Key words: Nondestructive testing (NDT), microwave, imaging, concrete, ground penetrating radar (GPR), finite difference-time domain (FD-TD), simulation, backpropagation.