Ultrasonic phased-array (PA) systems have been widely adopted in the field of nondestructive evaluation for material characterization and imaging of internal defects. Whereas many defects exhibit complex three-dimensional structures, most PA systems provide only two-dimensional images. In this Letter, we demonstrate the ability to create high-resolution 3D images of internal defects using a PA system based on a piezoelectric and laser ultrasonic system (PLUS). The PLUS combines a piezoelectric transmitter to insonify the structure to be inspected with a laser Doppler vibrometer to create a matrix array of receiver points without contact. The small size of the laser beam results in an ultra-multiple number of elements on the order of thousands, which is impossible to achieve with a conventional piezoelectric matrix array transducer. An emission from a piezoelectric transmitter compensates for the intrinsically low sensitivity of a laser Doppler vibrometer. After formulating the 3D imaging algorithm of the PLUS, we demonstrate that the PLUS with 4096 receiving points (i.e., 64 × 64 points) achieves high-resolution 3D imaging in a specimen with a flat bottom hole. We also visualize the complex structure of stress corrosion cracking. We believe that the 3D imaging capability of the PLUS may open up new avenues to the accurate evaluation of material strength, the identification of the types of defects, and the elucidation of the mechanisms of defect initiation.

中文翻译：

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面向固体 3D 超声成像的超高分辨率相控阵系统

超声波相控阵 (PA) 系统已广泛用于材料表征和内部缺陷成像的无损评估领域。尽管许多缺陷表现出复杂的三维结构，但大多数 PA 系统仅提供二维图像。在这封信中，我们展示了使用基于压电和激光超声系统 (PLUS) 的 PA 系统创建内部缺陷的高分辨率 3D 图像的能力。PLUS 结合了一个压电发射器，用激光多普勒测振仪对要检查的结构进行声波处理，以创建一个无接触的接收点矩阵阵列。激光束的小尺寸导致了数千个数量级的超多个元件，这是传统压电矩阵阵列换能器无法实现的。压电发射器的发射补偿了激光多普勒测振仪固有的低灵敏度。在制定了 PLUS 的 3D 成像算法后，我们证明了具有 4096 个接收点（即 64 × 64 点）的 PLUS 在具有平底孔的标本中实现了高分辨率 3D 成像。我们还可视化了应力腐蚀开裂的复杂结构。我们相信 PLUS 的 3D 成像能力可能为材料强度的准确评估、缺陷类型的识别以及缺陷引发机制的阐明开辟新的途径。我们证明了具有 4096 个接收点（即 64 × 64 点）的 PLUS 在具有平底孔的样品中实现了高分辨率 3D 成像。我们还可视化了应力腐蚀开裂的复杂结构。我们相信 PLUS 的 3D 成像能力可以为材料强度的准确评估、缺陷类型的识别以及缺陷引发机制的阐明开辟新的途径。我们证明了具有 4096 个接收点（即 64 × 64 点）的 PLUS 在具有平底孔的样品中实现了高分辨率 3D 成像。我们还可视化了应力腐蚀开裂的复杂结构。我们相信 PLUS 的 3D 成像能力可能为材料强度的准确评估、缺陷类型的识别以及缺陷引发机制的阐明开辟新的途径。