Non-contact inspection of construction materials using 3-axis multifunctional imaging system with microwave and laser sensing techniques

In this paper, the design of a 3-axis multifunctional imaging system with microwave and laser sensing techniques is described, and the results of its application to non-contact testing of construction materials are presented. This system can provide automated control of the movement of sensing units including a microwave antenna and a laser displacement sensor for contour following, optimization of standoff distance, and two imaging capabilities. First, the system is capable of generating images of the specimen under investigation using microwave data and displacement data, separately. In this case, the displacement data is used to generate 2-D images and a 1-D profile of the specimen surface while microwave images may provide information on interior structure of the specimen. Second, a combination of microwave and laser displacement sensor techniques can generate microwave images of the specimen by providing an optimal standoff distance and removing automatically, at hardware level, the change of the standoff distance. The applicability of the system to non-contact detection of metal and dielectric targets embedded in layered structures and flaws such as cracks on the surface of tilted and cylindrical specimens has been demonstrated.