Abstract
This paper presents a defect characterization method by spatio-temporal gradient analysis over the Lamb wave field. The surface ultrasound waves that propagate in the direction of the layer are potential candidates of non-destructive evaluation (NDE) methodology. The proposed method has an ability to classify the surface acoustic wave field through the rank of the covariance matrix defined over the four-dimensional vector space which is spanned by following components: a vertical displacement, its vertical velocity, and a pair of shear strains of the surface. The covariance matrix provides the information about defects. The determinant of the covariance matrix, therefore, is proposed as the index of homogeneity of the object surface. In this study, the computational process in wave field near the defects is discussed and their physical meanings are investigated through FDTD-simulations and acoustic experiments.
