Microwave nondestructive detection and evaluation of disbonding and delamination in layered-dielectric slabs

A microwave nondestructive technique for the detection and evaluation of disbonding and delamination in layered-dielectric-slabs backed by a conducting plate is discussed. The theoretical development of the technique is given. An incident wave illuminating such a medium is first considered, and the characteristics of the wave reflected by the metal plate are then formulated. An effective reflection coefficient whose phase characteristics are used in the detection and evaluation of delaminations in the media is determined in this way. The characteristics of this phase as a function of several parameters, such as delamination dielectric constant and thickness, slab dielectric constant, and thickness and the frequency of operation are investigated. The experimental apparatus is described. It was used to perform several experiments to test and verify the theory. Very good agreement was obtained between the theoretical and experimental results. In general, it was concluded that higher frequencies, thicker dielectric plates, and lower values of delamination dielectric constants tend to produce better results for evaluating the nature of a delaminated layer. This technique is simple and easily applicable to environments where these types of layered-slab are used