Ni Chen-Yin, Chen Chu, Ying Kai-Ning, Dai Lu-Nan, Yuan Ling, Kan Wei-Wei, Shen Zhong-Hua
School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China.
School of Science, Nanjing University of Science and Technology, Nanjing 210094, China.
Photoacoustics. 2021 Feb 27;22:100248. doi: 10.1016/j.pacs.2021.100248. eCollection 2021 Jun.
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.
激光超声（LU）技术已得到广泛研究。检测到的超声信号可使用合成孔径聚焦技术（SAFT）进一步处理，以检测内部缺陷并成像。基于LU的频域SAFT（F-SAFT）被开发用于可视化铝中的水平孔型缺陷。通过照射激光线源非破坏性地产生体声波，并使用激光多普勒测振仪在远离产生点的位置进行检测。通过速度映射研究这种非重合产生-检测对算法中使用的等效声速的影响。由于LU技术的宽带产生特性，对声波信号进行频率范围选择以提高信噪比（SNR）和重建速度。结果表明，通过使用LU F-SAFT算法，并结合速度映射和频率范围选择等优化方法，可以在三维空间中可视化小缺陷，缺陷位置得到校正，图像质量得到提高。
