In the field of non-destructive evaluation of structures, 2D and 3D imaging of internal flaws is a critical task. Defect imaging allows making informed follow-up decisions based on the morphology of the flaw. This paper will present advances in ultrasonic tomography for the 2D and 3D visualization of internal flaws in solids. In particular, improvements to the conventional tomographic imaging algorithms have been made by utilizing a mode-selective image reconstruction scheme that exploits the specific displacement field, respectively, of the longitudinal wave modes and the shear wave modes, both propagating simultaneously in the test volume. The specific mode structure is exploited by an adaptive weight assignment to the ultrasonic tomographic array. Such adaptive weighting forces the imaging array to look at a specific scan direction and better focus the imaging onto the actual flaw (ultrasound reflector). Moreover, the introduction of a global matched coefficient, computed through the matching of measured and expected times of flight for each pixel, is illustrated. The benefits deriving from the application of this coefficient to conventional imaging frameworks are shown. This study shows that the adaptive weighing based on wave structure and the integration of the global matched coefficient improve image contrast and resolution compared to a conventional ultrasonic imaging technique based on a delay-and-sum or minimum variance distortionless method. Results will be shown from experimental tests of simulated flaws in solids.
Simone Sternini, Thompson Vu Nguyen, and Francesco Lanza di Scalea, "Ultrasonic imaging using wave structure-based weights and global matched coefficients," Proc. SPIE 9805, Health Monitoring of Structural and Biological Systems 2016, 980527 (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 24, 2016; Published: 1 April 2016); https://doi.org/10.1117/12.2218931.
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