Research On FDTD Method To Electromagnetic Scattering Problems In Microwave Imaging For Reinforced Concrete Structure

With the development of the electromagnetic theory and the improvement of the computer performance, the computational electromagnetism has been developed fatherly in recent years. Finite Difference Time Domain (FDTD) method is an important method of computational electromagnetic research. It alternately samples chronological electric and magnetic fields, meshes the electric field into Yee unit, that is to say, disperses Maxwell's equations into the explicit differential equations, and gets the iterative solution. Therefore, with the initial value of given reply electromagnetic problem, the FDTD method is able to get the electromagnetic field distribution in space at anytime step by step. Here will take the FDTD method to solve practical problems.In this paper, microwave dissemination in the reinforced concrete as research subjects for questions compute and research. The specific problem-solving steps are given according to basic idea of FDTD and the microwave detection principle of the reinforced concrete structure. Including calculating the microwave frequency band of measuring reinforced concrete structure, meshing the model, differential equations describing high-frequency electromagnetic fields from Maxwell's equations to difference calculate for each Yee unit, loading the plane wave to the boundary of the total field with 0 degree according to the condition of its accession, and in the outer layer truncating the simulation region with PML, using this model to simulate the scatting of reinforced concrete in infinite space. In the selection of the absorbing boundary, this paper programming two absorbing boundaries to simulate propagation of wave in free space with MATLAB. From the theoretical comparison to the numerical simulation, it is found that the PML absorbing boundary condition is superior to Mur absorbing boundary condition.Finally, Variable specification reinforced concrete models are built and simulation is made on 3.0GHz microwave frequency by using Fortran programming language. By this way, electric field intensity-location relation image is received. It displays steel bar distributing situation in concrete intuitively. Compare with the normalized simulation result of ANSYS, the curves superposition degree is satisfying with small error. The results indicate that the whole design is reasonable. It is feasible and convenient to realize nondestructive testing for reinforced concrete structure by using FDTD method.