Ying Kai-Ning, Ni Chen-Yin, Dai Lu-Nan, Yuan Ling, Kan Wei-Wei, Shen Zhong-Hua
School of Science, Nanjing University of Science and Technology, Nanjing 210094, China.
School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China.
Photoacoustics. 2022 May 14;27:100370. doi: 10.1016/j.pacs.2022.100370. eCollection 2022 Sep.
The Synthetic Aperture Focusing Technique (SAFT) is an imaging algorithm used in laser ultrasonics (LU) to visualise the appearance of defects. However, ultrasound excited by a pulsed laser has the characteristics of wide bandwidth and multi-mode directivity patterns, leading to common problems in the SAFT process, such as low utilisation of ultrasound information and possible artefacts. To solve these problems, a Multi-mode Time-domain SAFT (MMT-SAFT) algorithm is proposed in this paper. The influence of ultrasonic directivity is discussed according to the imaging depth range, and imaging with multiple LU modes is performed to reduce artefacts. Simulations and experimental results prove the feasibility of the MMT-SAFT algorithm, which not only presents a clearer image of the upper part of defects but also improves image quality compared with time-domain SAFT using a single ultrasonic mode. The proposed technique can provide feasible directions for laser ultrasonic defect imaging.
合成孔径聚焦技术（SAFT）是一种用于激光超声（LU）的成像算法，用于可视化缺陷的外观。然而，脉冲激光激发的超声波具有宽带宽和多模方向性图案的特点，导致SAFT过程中存在常见问题，如超声信息利用率低和可能出现的伪像。为了解决这些问题，本文提出了一种多模时域SAFT（MMT-SAFT）算法。根据成像深度范围讨论了超声方向性的影响，并采用多种LU模式进行成像以减少伪像。仿真和实验结果证明了MMT-SAFT算法的可行性，该算法不仅能更清晰地呈现缺陷上部的图像，而且与时域SAFT使用单一超声模式相比，还提高了图像质量。所提出的技术可为激光超声缺陷成像提供可行的方向。
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