Cai Bowen, Bo Luyu, Campbell Andrew, Li Jiali, Qiu Chongpeng, Liu Hongye, Yu Lingyu, Tian Zhenhua
Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061, USA.
Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29208, USA.
Ultrasonics. 2025 Aug 6;157:107787. doi: 10.1016/j.ultras.2025.107787.
Guided wave phased arrays, which use multiple sensors in compact patterns to perform damage imaging through phase delays, have garnered significant interest for the rapid inspection of large composite panels. Previous phased arrays typically used large, wired ultrasonic transducers attached to composites, limiting array reconfigurability and preventing contactless inspection from a distance. This study presents a fully noncontact guided wave phased array imaging approach, which utilizes a dual laser-based guided wave generation and sensing system, namely a pulsed laser-scanning laser Doppler vibrometer (PL-SLDV) system, along with synthetic phased array beamforming and wavefield analysis. The PL-SLDV system employs a Q-switched PL module to generate nanosecond laser pulses that excite ultrasonic guided waves through the thermoelastic effect. To ensure consistent laser-to-ultrasound energy conversion across different composites and prevent potential thermal damage to composites, the laser pulses are directed onto a thin aluminum patch bonded on the composite. The SLDV acquires guided wave signals based on the Doppler effect, and its integrated galvo mirrors can quickly steer laser beam directions to scan a composite plate, thereby acquiring guided wave signals at various array points. Time/phase delays are then applied to the acquired signals through post-processing for synthetic phased array beamforming. To generate inspection images using the acquired wave signals, an improved delay-and-sum (DAS) imaging algorithm is introduced. It uses adaptive weighting factors and incorporates phase delay and back-propagation phase shift, accounting for the frequency- and direction-dependent dispersion relation, to overcome the dispersion effect and directional dependency of waves in anisotropic materials. Moreover, the fusion of phased array imaging and a wavefield analysis approach, which can extract frequency-wavenumber dispersion relations from experimental wavefields, enables our phased array method to perform damage imaging without requiring prior knowledge of composite properties, such as mechanical properties or theoretical dispersion curves. Additionally, the noncontact wave generation/acquisition feature of our PL-SLDV system allows for inspecting composites from a distance and easily constructing phased arrays with different patterns. Proof-of-concept experiments demonstrate that multiple defects in different directions can be successfully detected. Additionally, this study reveals that PL-generated guided waves can contain multiple modes, such as A, S, SH, A, S, and SH modes, offering valuable insights for researchers interested in using PL-generated guided waves.
导波相控阵通过紧凑排列的多个传感器利用相位延迟进行损伤成像，在大型复合材料面板的快速检测方面引起了广泛关注。以往的相控阵通常使用连接在复合材料上的大型有线超声换能器，限制了阵列的可重构性，且无法进行远距离非接触检测。本研究提出了一种完全非接触的导波相控阵成像方法，该方法利用基于双激光的导波产生和传感系统，即脉冲激光扫描激光多普勒测振仪（PL-SLDV）系统，结合合成相控阵波束形成和波场分析。PL-SLDV系统采用调Q脉冲激光模块产生纳秒激光脉冲，通过热弹性效应激发超声导波。为确保在不同复合材料上激光到超声的能量转换一致，并防止对复合材料造成潜在热损伤，激光脉冲被导向粘贴在复合材料上的薄铝片。激光多普勒测振仪基于多普勒效应获取导波信号，其集成的振镜可快速改变激光束方向以扫描复合材料板，从而在不同阵列点获取导波信号。然后通过后处理对采集到的信号应用时间/相位延迟进行合成相控阵波束形成。为了利用采集到的波信号生成检测图像，引入了一种改进的延迟求和（DAS）成像算法。该算法使用自适应加权因子，并结合相位延迟和反向传播相移，考虑了频率和方向相关的色散关系，以克服各向异性材料中波的色散效应和方向依赖性。此外，相控阵成像与波场分析方法的融合，能够从实验波场中提取频率-波数色散关系，使我们的相控阵方法在无需复合材料特性（如力学性能或理论色散曲线）先验知识的情况下进行损伤成像。此外，我们的PL-SLDV系统的非接触波产生/采集特性允许从远距离检测复合材料，并轻松构建具有不同图案的相控阵。概念验证实验表明，可以成功检测到不同方向的多个缺陷。此外，本研究还表明，脉冲激光产生的导波可以包含多种模式，如A、S、SH模式，为对使用脉冲激光产生的导波感兴趣的研究人员提供了有价值的见解。
