Microwave Imaging of Layered Structures in Civil Engineering

This work is devoted to the reconstruction of layered dielectric structures in civil engineering using solution of inverse problem, when the measured reflection coefficient is given in frequency domain. The two-stage iterative technique has been applied to derive the permittivity profile. In the first stage, positions of the reflecting interfaces are obtained by the inverse Fourier transform of the reflection coefficient. Then, the unknown profile is represented in the form of steps built on the interfaces, with the step amplitudes being determined from a linear integral equation. The whole procedure is repeated several times until the convergence criterion is satisfied. To improve the form of the reconstructed dielectric profile, we used in this work step functions of finite width instead of abrupt Heaviside steps. Besides, the input reflection coefficient data before the inversion have been preprocessed by a free-space calibration method. The inversion technique has been successfully applied to reconstruct layered building constructions using real experimental data in the conditions of poor resolution and weak response of the reconstructed interface.