Location

Snowmass Village, CO

Start Date

1-1-1995 12:00 AM

Description

The focused transducer combined with C-scan imaging is currently the workhorse of ultrasonic nondestructive evaluation (NDE) [1]. Its strength lies in its simplicity and high quality images. There is room for improvement, however. First, the lateral resolution of C-scan images is inversely proportional the diameter of the transducer. At a given operating frequency, the diameter of a transducer cannot be made arbitrarily large due to the accompanying increase in capacitance. Another limitation is that the depth of field of a focused transducer is proportional to its beam width. So the depth of field is relatively short for high resolution images requiring the use of multiple transducers which focus at different depths. Finally, the transducer has difficulty achieving consistent focus when inspecting parts with contoured surfaces. With the advent of computed imaging [2], many of the limitations of the focused transducer can be circumvented by sophisticated image reconstruction algorithms implemented on high-speed computers. One such image reconstruction algorithm is the Synthetic Aperture Focusing Technique (SAFT) [3]. The idea behind SAFT is to synthesize an aperture by coherently combining data from a set of transducer positions to form an image point. In a typical SAFT implementation, the raw data is obtained by digitizing the RF-waveforms from a scanned transducer focused on the surface of the part (see Fig. 1a). Subsequently, the A-scans are coherently combined to form focused images of the parf’s interior.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

14A

Chapter

Chapter 3: Interpretive Signal Processing and Image Analysis

Section

Imaging and Reconstruction

Pages

901-908

DOI

10.1007/978-1-4615-1987-4_113

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Ultrasonic Maximum Aperture Saft Imaging

Snowmass Village, CO

The focused transducer combined with C-scan imaging is currently the workhorse of ultrasonic nondestructive evaluation (NDE) [1]. Its strength lies in its simplicity and high quality images. There is room for improvement, however. First, the lateral resolution of C-scan images is inversely proportional the diameter of the transducer. At a given operating frequency, the diameter of a transducer cannot be made arbitrarily large due to the accompanying increase in capacitance. Another limitation is that the depth of field of a focused transducer is proportional to its beam width. So the depth of field is relatively short for high resolution images requiring the use of multiple transducers which focus at different depths. Finally, the transducer has difficulty achieving consistent focus when inspecting parts with contoured surfaces. With the advent of computed imaging [2], many of the limitations of the focused transducer can be circumvented by sophisticated image reconstruction algorithms implemented on high-speed computers. One such image reconstruction algorithm is the Synthetic Aperture Focusing Technique (SAFT) [3]. The idea behind SAFT is to synthesize an aperture by coherently combining data from a set of transducer positions to form an image point. In a typical SAFT implementation, the raw data is obtained by digitizing the RF-waveforms from a scanned transducer focused on the surface of the part (see Fig. 1a). Subsequently, the A-scans are coherently combined to form focused images of the parf’s interior.