PNNL

Abstract

This study compares selected analytical approaches for imaging a near-surface resin-rich defect in a thin graphite/epoxy plate with the use of backscattered ultrasound. The same backscattered waveforms were used to produce peak-to-peak, signal energy, and entropy images. All of the entropy images exhibit better border delineation and defect contrast than the either peak-to-peak or signal energy. The best results are obtained with the use of the joint entropy of the backscattered waveforms with a reference function. Two different references are examined. The first is a reflection of the insonifying pulse from a stainless steel reflector. The second is an approximate optimum obtained from an iterative parametric search. The joint entropy images produced using this reference exhibit three times the contrast obtained in previous studies.