Elsevier

Photoacoustics

Volume 22, June 2021, 100248
Photoacoustics

Research article
Non-destructive laser-ultrasonic Synthetic Aperture Focusing Technique (SAFT) for 3D visualization of defects

https://doi.org/10.1016/j.pacs.2021.100248Get rights and content
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Highlights

  • LU-based F-SAFT algorithm is developed, a defect of ϕ=0.2 mm is visualized.

  • Non-destructive visualization of defects with line LU source.

  • Improved target depth detection by velocity mapping with separated laser sources.

  • Frequency range selected for improving SNR and reducing calculation time.

Abstract

The Laser Ultrasonic (LU) technique has been widely studied. Detected ultrasonic signals can be further processed using Synthetic Aperture Focusing Techniques (SAFTs), to detect and image internal defects. LU-based SAFT in frequency-domain (F-SAFT) is developed to visualize horizontal hole-type defects in aluminum. Bulk acoustic waves are non-destructively generated by irradiating a laser line-source, and detected using a laser Doppler vibrometer at a point away from the generation. The influence of this non-coincident generation-detection on the equivalent acoustic velocity used in the algorithm is studied via velocity mappings. Because the wide-band generation characteristic of the LU technique, frequency range selections in acoustic wave signals are implemented to increase Signal-to-Noise Ratio (SNR) and reconstruction speed. Results indicate that by using the LU F-SAFT algorithm, and incorporating optimizations such as velocity mapping and frequency range selection, small defects can be visualized in 3D with corrected locations and improved image quality.

Keywords

Laser ultrasound
Synthetic Aperture Focusing Technique (SAFT)
Non-destructive Test (NDT)
Imaging algorithm

Cited by (0)

Chen-Yin Ni is an Associate Professor at School of Electronic and Optical Engineering, Nanjing University of Science and Technology. Dr. NI received his Ph.D. from School of Science, Nanjing University of Science and Technology. He has expertise in applications of laser-generated ultrasound in non-destructive evaluation, laser interaction with materials, research involving optical, thermal materials science and other interdisciplinary areas of knowledge and technology.

Chu Chen is currently an Optical Engineering Graduate from School of Electronic and Optical Engineering, Nanjing University of Science and Technology. CHEN’s research work is supervised by Chen-Yin NI and Wei-Wei KAN. Recently, CHEN and her colleagues have devoted themselves to the research of Synthetic Aperture Focusing Technology using laser ultrasonic approaches.

Kai-Ning Ying is currently as a Biomedical Engineering Graduate from School of Electronic and Optical Engineering, Nanjing University of Science and Technology. He will continue his PhD in School of Science NJUST. Now his research focuses on Photoacoustic Tomography, Laser Ultrasound and Synthetic Aperture Focusing Technology.

Lu-Nan Dai is currently as a Ph.D. student major in Optical Engineering in School of Science, Nanjing University of Science and Technology supervised by Chen-Yin NI and Zhong-Hua SHEN. DAI is interested in Laser Ultrasound based NDT&E, especially LU based Synthetic Aperture Focusing Technology.

Ling Yuan, Associate Professor at School of Science, Nanjing University of Science and Technology. In 2008, Dr. YUAN graduated from Nanjing University of Science and Technology with a doctorate degree in optical engineering. Since 2008, Dr. YUAN has been engaged in teaching and scientific research in the School of Science, Nanjing University of Science and Technology. Her research directions are photoacoustic nondestructive testing, laser matter interaction mechanism and application.

Weiwei Kan received his Ph.D. from Nanjing University in 2015. He is currently an Associate Professor at School of Science, Nanjing University of Science and Technology. He acquired his teaching qualification in 2017 and began delivering the course of photoacoustics since then. His current research interest includes acoustic artificial materials, ultrasound imaging and laser ultrasound.

Zhong-Hua Shen is a Professor and Ph.D. supervisor of Nanjing University of Science and Technology. In 1999, she graduated from Nanjing University of Science and Technology with a doctorate degree in optical engineering. Since 2001, she has started working at Nanjing University of Science and Technology. Her research directions are laser ultrasonic non-destructive testing technology and application, laser-substance interaction mechanism and testing. From 2004–2009, she has visited the University of Heidelberg in Germany frequently and has established collaborations with many internationally renowned photoacoustic research groups.

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These authors contributed equally to this work.