title: Inverse wave field extrapolation: a different NDI approach to imaging defects.
abstract: Nondestructive inspection (NDI) based on ultrasound is widely used. A relatively recent development for industrial applications is the use of ultrasonic array technology. Here, ultrasonic beams generated by array transducers are controlled by a computer. This makes the use of arrays more flexible than conventional single-element transducers. However, the inspection techniques have principally remained unchanged. As a consequence, the properties of these techniques, as far as characterization and sizing are concerned, have not improved. For further improvement, in this paper we apply imaging theory developed for seismic exploration of oil and gas fields on the NDI application. Synthetic data obtained from finite difference simulations is used to illustrate the principle of imaging. Measured data is obtained with a 64-element linear array (4 MHz) on a 20-mm thick steel block with a bore hole to illustrate the imaging approach. Furthermore, three examples of real data are presented, representing a lack of fusion defect, a surface breaking crack, and porosity.
authors.affiliation: Röntgen Technische Dienst, Rotterdam, Zuid-Holland, The Netherlands. n.portzgen@rtd.nl
authors.forename: Niels
authors.initials: N
authors.lastname: Pörtzgen
authors.forename: Dries
authors.initials: D
authors.lastname: Gisolf
authors.forename: Gerrit
authors.initials: G
authors.lastname: Blacquière
mesh_terms: D000465:Algorithms; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D016247:Information Storage and Retrieval / Q000379:methods; D008420:Manufactured Materials / Q000032:analysis*; D008422:Materials Testing / Q000379:methods*; D009716:Numerical Analysis, Computer-Assisted; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014463:Ultrasonography / Q000379:methods*