Dynamic weighted phase shift migration for the ultrasonic phased array imaging of wrinkles in thick composites

A dynamic weighted phase shift migration (DW-PSM) is proposed to detect wrinkles of high depth, i.e., larger than 10 mm, in thick fiber reinforced composites with ultrasonic phased arrays. The weighting factors are first introduced for the attenuation and dispersion respectively into modified K-K relations. A pre-processing procedure is then applied to correct the instantaneous phase difference into equal between adjacent layers. After evaluating the effective attenuation coefficients by averaging through all the phased array elements, an optimal weighting factor ratio is determined for each sample. Different to the depth information loss with classical PSM, wrinkles located at 11 mm, 15 mm, and 16 mm can be identified eventually in 18 mm hybrid carbon/glass fiber composite samples based on DW-PSM. A great resolution can be obtained by adopting appropriate frequency, weighting factors and migration steps. The detection errors of wrinkle angles are only 1.97 %, 2.38 %, and 2.42 %, respectively.