Investigation of embedded structures in media with unknown acoustic properties

For the nondestructive evaluation of components with ultrasound a priori information about the specimen is necessary. So the time of flight to a defect is measured and, with known sound velocity, it is possible to determine the correct location of the defect. In general, the sound velocity is assumed as known. If it is not known, the sound velocity has to be determined additionally. This can be done, for example, by measuring the time of flight to the backwall with ultrasound and the thickness of the specimen with a caliper gauge. However, this is impossible to realize with single-sided access to the specimen. For determining the size of inclusions, several techniques like the half-value method or the DGS-method (Distance Gain Size) are established. These methods are based on the assumption of (circular) plane reflectors. Therefore, they cannot be applied on the size determination of inclusions with curved surfaces.