Dual-laser integrated microwave imaging system for nondestructive testing of construction materials and structures

Microwave near-field imaging techniques have been successfully used for the nondestructive testing of construction materials in civil infrastructures. In this technique, the distance between the microwave antenna and the material, which is referred to as standoff distance is an important parameter. The standoff distance should be kept constant during the scanning process or there should be a proper compensation method to overcome any change in the distance. The undesired change in the standoff distance may mask the indication of flaws. However, civil infrastructures are composed of construction materials with different geometrical shapes and sharp edges, and maintaining the constant standoff distance during the scanning process is a challenging task. For this purpose, a novel dual-laser integrated microwave imaging system is proposed. The proposed system consists of a novel integrated sensing unit with two laser displacement sensors and a single microwave antenna that automatically follows the contour of the material under test at a constant standoff distance and generates microwave images. The proposed system performs contour following at hardware level and does not require any calibration or complex compensation algorithm. The comparison of two microwave antennas is performed to find the suitable antenna for different materials. The proof of concept of the developed system for the nondestructive testing of construction materials with different geometrical shapes is provided.