Location

La Jolla ,CA

Start Date

1-1-1989 12:00 AM

Description

Ultrasonic non-destructive testing (NDT) techniques are widely used to detect flaws or defects within structural and functional components, and to classify and characterize the defects by their size, shape, location, orientation etc. Techniques which have been used include: A-scan, B-scan and Synthetic Aperture Focusing Technique (SAFT). Of these, A-scan is difficult to interpret without extensive operator training, and may lead to unreliable inspections. B-scan is easy to interpret, but it also has some disadvantages, such as that forming a B-scan image with an unfocused transducer leads to poor lateral resolution, and if using a focused transducer, the dynamic focusing technique has to be used to obtain good lateral resolution in all the regions of interest. SAFT, on the other hand, can get an image with good lateral resolution in all the regions of interest. The basic principle of SAFT is to apply a signal processing algorithm to a collection of raw A-line data from different transducer positions. The algorithm allows each point within the inspected volume to be focused upon by mathematically simulating the action of a lens. This algorithm involves the summation of the raw RF data shifted by predicted time delay. SAFT has been used for the fine grained materials ultrasonic evaluation with excellent results [9] [10]. However, use of SAFT in coarse grained material results in an image which suffers from ultrasonic speckle. The presence of speckle reduces the detectability of targets. This problem is also encountered in ultrasonic A-scan and B-scan coarse grained material testing.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

8A

Chapter

Chapter 3: Interpretive Signal and Image Processing

Section

Image and Signal Processing

Pages

727-734

DOI

10.1007/978-1-4613-0817-1_91

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Speckle Reduction in Ultrasonic SAFT Images in Coarse Grained Material Through Split Spectrum Processing

La Jolla ,CA

Ultrasonic non-destructive testing (NDT) techniques are widely used to detect flaws or defects within structural and functional components, and to classify and characterize the defects by their size, shape, location, orientation etc. Techniques which have been used include: A-scan, B-scan and Synthetic Aperture Focusing Technique (SAFT). Of these, A-scan is difficult to interpret without extensive operator training, and may lead to unreliable inspections. B-scan is easy to interpret, but it also has some disadvantages, such as that forming a B-scan image with an unfocused transducer leads to poor lateral resolution, and if using a focused transducer, the dynamic focusing technique has to be used to obtain good lateral resolution in all the regions of interest. SAFT, on the other hand, can get an image with good lateral resolution in all the regions of interest. The basic principle of SAFT is to apply a signal processing algorithm to a collection of raw A-line data from different transducer positions. The algorithm allows each point within the inspected volume to be focused upon by mathematically simulating the action of a lens. This algorithm involves the summation of the raw RF data shifted by predicted time delay. SAFT has been used for the fine grained materials ultrasonic evaluation with excellent results [9] [10]. However, use of SAFT in coarse grained material results in an image which suffers from ultrasonic speckle. The presence of speckle reduces the detectability of targets. This problem is also encountered in ultrasonic A-scan and B-scan coarse grained material testing.