Volume 34, Issue 1 (January 2006)
Ultrasonic Synthetic Aperture Imaging for Correcting the Refraction Artifacts Applied to Angle Beam Immersion Testing
The ultrasonic angle beam immersion testing is a commonly used ultrasonic nondestructive testing technique for automatically detecting nonhorizontal flaws. Since the physical characteristics of the liquid of the couplant is always largely different from those of the test object, a strong refraction of ultrasound occurs at the interface if the angle of incidence is not normal. This will increase the difficulty of estimating the size and position of the flaw from the image obtained by angle beam immersion testing.
Due to the rapid progress in computer technology, the flaw image may be reconstructed with better resolution in real time (or near real time) using the digital signal processing method. Therefore, a synthetic aperture focusing technique, which corrects the refracted effect, is proposed to reconstruct the image obtained from angle beam immersion testing. After processing, the position and size of the flaw can be directly read from the processed image. Two specimens were fabricated and scanned, and the scan images were processed using this technique to verify this imaging technique. The experimental results show that the position and size of the flaw can be directly and accurately estimated from the processed image.