Investigation of the 1-D inverse born technique

An ultrasonic digital signal processing technique which can be used to size isolated inhomogeneities in an otherwise homogeneous medium is examined. The technique is known as Born inversion and is theoretically valid for application to weak scatterers. However, accurate radius predictions have also been obtained experimentally for strong scatterers (voids). The technique was examined using synthetically generated ultrasonic signals from weak and strong scatterers, as well as experimental data from voids in high strength metals, to ascertain the application limits of the algorithm and to investigate why the technique is insensitive to different classes of scatterer. It was found that the part of the frequency spectrum used in the inversion routine has a very similar profile for weak and strong scatterers. Accurate sizing using Born inversion is only obtained if the bandwidth of the interrogating probe is adequate. However, the probe bandwidth requirements depend on the size of the flaw being examined, which is not known a priori. A methodology is presented which determines whether the match of flaw size to probe bandwidth is suitable. This has proved critical in obtaining accurate size estimates from the inversion.