Allowing for inhomogeneous anisotropy of a welded joint when reconstructing reflector images from echo signals received by an ultrasonic antenna array

Resumo

In order to improve the quality of reflector images in welded joints, a modification of the C-SAFT algorithm has been proposed that allows for inhomogeneous anisotropic properties of a test object. Two algorithms have been considered for calculating the times of delay of propagation of a pulse along a ray, viz. a geometrical ray-construction algorithm and an algorithm based on the ray tube description. The geometrical algorithm proceeds from the assumption that an inhomogeneous anisotropic medium can be divided into a set of homogeneous anisotropic layers. Ray construction is performed with allowance for ray refraction on the boundaries of these layers. The geometrical algorithm makes it possible to allow for two types of waves, their conversion, and uneven boundaries of the domains in the test object. Special cases of ray propagation have been considered that demonstrate limitations of calculating delay times by geometrical tracing. The algorithm based on the ray tube description is more versatile and makes it possible to calculate not only the propagation time of a pulse along a ray in an inhomogeneous anisotropic medium but also the pulse amplitude. The operability of the proposed approach has been demonstrated by numerical experiments on processing echo signals that have been calculated by the method of finite differences in a time domain.