Microvawe Imaging for Nondestructive Evaluation of Civil Structures

Subsurface imaging of civil structures is a subject of growing interest because of the need check the integrity of buildings, roads, and bridges in a non-invasive (and certainly nondestructive way). In this framework, this study is aimed at presenting a microwave imaging technique for crack or failure detection. The proposed approach is based on a numerically computed Green's function and on an effective evolutionary optimization technique. In order to evaluate the achieved results and to assess the effectiveness and current limitations of the proposed approach, a set of selected numerical simulation is presented. Introduction: Non-invasive diagnostics methods based on microwaves are currently used in various applications ranging from industrial and civil engineering to geophysical monitoring and biomedical analysis [1]-[4]. In this framework, microwave tomographic approaches have been recently proposed. [5]-[7]. Starting from the knowledge of the fields scattered from an unknown sample under test illuminated by means of a known probing electromagnetic source, these techniques are aimed at determining the distribution of the dielectric characteristics of the whole investigation domain. However, such a redundant information is not needed in non-destructive evaluation (NDE) and non-destructive testing (NDT) applications. Generally, only the reconstruction of a small defect buried in a completely known host medium is required. Consequently, customized approaches have been developed [8]-[10]. More in detail, these approaches resort to a parameterization of the unknown defect, assumed of rectangular shape, by defining some key features as the position, the dimensions and the orientation. Then, the inverse problem to be handled turns out to be notably simplified with a reduction of the overall computational burden for the optimization procedure. In this paper, an effective method called Inhomogeneous Green's based Approach (IGA), belonging to the class of NDE/NDT customized strategies, is applied to the civil engineering scenarios. The paper is organized as follows. After a brief presentation of the mathematical formulation (Sect. " Mathematical Formulation "), a numerical validation will be presented by considering selected experiments (Sect. " Numerical Validation "). Finally, some conclusion will be reported (Sect. " Conclusions "). Mathematical Formulation: Let us consider a standard inverse scattering problem (Fig. 1), where a two-dimensional scenario is illuminated by a set of V known electromagnetic sources radiating electric fields ,) , (y x E v inc V v ,..., 1 = .