3d Microwave Imaging Technology Using Antenna Array for Damage Assessment of Concrete Structure

Various nondestructive evaluation (NDE) techniques have been studied to locate steel rebars or dowels, and to detect invisible damage such as voids and cracks inside concrete and debonding between rebars and concrete caused by corrosions and earthquakes. In this study, 3-dimensional (3D) microwave imaging technology was developed to detect such damage and to locate steel rebars or dowels. Extending their earlier analytical work on 2D image reconstruction, the authors have developed an imaging algorithm with visualization software for reconstructing a 3D volume image. This paper presents a numerical focusing procedure, which allows the recovery of a 3D object from its scattered field. A multi-frequency technique was applied in order to improve the quality of the reconstructed image. The effectiveness of the numerical focusing and the multi-frequency techniques was demonstrated through numerical simulations. Furthermore, innovative design of the antenna array is described, in which a hybrid approach for network distribution was used.