Acoustic near-field imaging of defects based on the dynamic shear strain analysis

A Quantitative acoustical imaging technology is used or developed to classify the region of defect. This method estimates characteristics of the elasticity of a region of interest having somewhat inhomogeneity contrasted to the surrounding materials. However, strong incident waves overlap with the weak scattered waves, which are difficult to be interpreted from the observed signals. The proposed nearfield imaging method can be summarized as follows. 1) The distributions of the normal displacement of the object surface is governed by the 2-dimensional wave equation in the Lamb-wave field. 2) When the single propagating wave front exists on the surface of the object with no defect, the orthogonal pair of the out-of-plane shear strains are linearly dependent each other. Therefore the determinant of a covariance matrix which is composed of the orthogonal pair of the shear strains becomes zero. 3) When a region of interest having somewhat inhomogeneity exists, scattered wave arises in the Lamb-wave field. Consequentry, the determinant becomes larger than zero because of the independency between the orthogonal pair over the region of the scattered and incident wave field.