Defect imaging and characterization in composite structures using near-field microwave nondestructive testing techniques

The use of composites as building materials in different industries, aircrafts, cars, ships, buildings, bridges, etc., is rapidly growing. Composite structures become weaker than expected due to the presence of an inhomogeneity or a disbond within their layers. The presence of these defects can cause catastrophic results unless their presence is detected and their effects are assessed. Microwave nondestructive imaging techniques have several unique attributes which make them attractive for inspecting composite structures. Near-field microwave imaging is based on transmitting a wave into a dielectric structure, which is located in the near-field of a sensor, and using a signal proportional to the magnitude or phase of the transmitted or reflected wave to create a two or three dimensional image of the structure under investigation. To analyze the features and properties of an experimental image, it is important to form and optimize the image theoretically before application. In this paper, we will present the image formation model and illustrate its potential on optimizing the detection capability of subsurface inclusions in multi-layered composites.