Microwave Nondestructive Evaluation of Disbonds Under Anechoic Tiles.

An experimental and theoretical study of a microwave nondestructive inspection technique to detect the presence of and evaluate the thickness of disbonds between anechoic tiles and the hull of the COLLINS class submarine is presented. The magnitude and phase of a reflected microwave signal in the absence and presence of a disbond is measured as a function of disbond thickness and frequency for i a layer of anechoic tile material and ii a COLLINS anechoic tile, both backed by a flat conducting plate. Disbond thicknesses of 0.0 to 1.5 mm are considered over a frequency range of 2 to 18 GHz. The results are in good agreement with theoretical predictions and clearly indicate that disbonds of 0.1 mm can be easily detected. Further development and potential problems are also described.