Ultrasonic-image reconstruction with surface mapping and synthetic-aperture techniques
Synthetic-aperture image-enhancement techniques have been used to improve the resolution in ultrasonic images. In general it is believed that global surface variations will not degrade the resolution of the image but only produce errors in the location of the image relative to the actual location of the flaw. A sample which has a surface variation which is not untypical of the shrinkage around a weld is imaged in ultrasound. The image produced with standard synthetic-aperture enhancement which does not include corrections for the surface variations is of no better quality than the unenhanced image. The image produced accounting for the surface variations by using the front surface echo to map the surface does resolve the flaws. However, due to transducer side-lobe interference, the front-surface echo does not map the surface accurately enough for the enhancement algorithm to produce precise locations for the images of the flaws. Enhanced images of targets viewed with ultrasonic shear waves also show improved resolution. However, the problems with transducer side-lobes interfering with the front surface echo are worse with shear waves. Also the reconstruction process is more complex. Both these lead to inaccuracies in the locations of the flaws. Phase and amplitude measurements of waves reflected from a crack as a function of frequency and aperture position show promise of discriminating crack size. Measurements made on stainless-steel bars with fatigue cracks are discussed.
- Research Organization:
- EG and G Idaho, Inc., Idaho Falls (USA)
- DOE Contract Number:
- AC07-76ID01570
- OSTI ID:
- 6432991
- Report Number(s):
- EGG-FM-5667; ON: DE83009197
- Country of Publication:
- United States
- Language:
- English
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