Wavefield imaging is a powerful visualization tool in nondestructive evaluation for studying ultrasonic wave propagation and its interactions with damage. To isolate and study damage scattering, damage-free baseline data is often subtracted from a wavefield. This is often necessary because the damage wavefield can be orders of magnitude weaker than the incident waves. Yet, baselines are not always accessible. When the baselines are accessible, the experimental conditions for the baseline and test data must be extremely similar. Researchers have created several baseline-free approaches for isolating damage wavefields, but these often rely on specific experimental setups. In this paper, we discuss a flexible approach based on ultrasonic guided wave digital surrogates (i.e., numerical simulations of incident waves) and transfer learning. We demonstrate this approach with two setups. We first isolate reflections from a circular, 2 mm diameter half-thickness hole on a 10 × 10 cm steel plate. We then isolate 8 circular, half-thickness holes of various diameters from 1 mm to 40 mm on a 60 × 60 cm steel plate. The second plate has a non-square geometry and the data has multi-path reflections. With both data sets, we isolate damage reflections without explicit experimental baselines. We also briefly illustrate the comparison of our dictionary learning method with wavenumber filtering technique which is often used to enhance the defect wavefields.

中文翻译：

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Sim-to-Real：采用超声导波数字替代和迁移学习进行损伤可视化

波场成像是一种强大的无损评估可视化工具，用于研究超声波传播及其与损伤的相互作用。为了隔离和研究损伤散射，通常从波场中减去无损伤基线数据。这通常是必要的，因为损伤波场可能比入射波弱几个数量级。然而，基线并不总是可以访问的。当基线可访问时，基线和测试数据的实验条件必须极其相似。研究人员已经创建了几种用于隔离损伤波场的无基线方法，但这些方法通常依赖于特定的实验设置。在本文中，我们讨论了一种基于超声导波数字代理（即入射波的数值模拟）和转移学习的灵活方法。我们通过两种设置演示了这种方法。我们首先从 10 × 10 cm 钢板上的一个直径为 2 mm 的圆形孔中隔离反射。然后，我们在 60 × 60 厘米的钢板上隔离 8 个直径从 1 毫米到 40 毫米不等的圆形半厚度孔。第二块板具有非方形几何形状，数据具有多路径反射。使用这两个数据集，我们在没有明确实验基线的情况下隔离了损伤反射。我们还简要说明了我们的字典学习方法与通常用于增强缺陷波场的波数滤波技术的比较。在 60 × 60 cm 的钢板上开出 1 mm 到 40 mm 各种直径的半厚孔。第二块板具有非方形几何形状，数据具有多路径反射。使用这两个数据集，我们在没有明确实验基线的情况下隔离了损伤反射。我们还简要说明了我们的字典学习方法与通常用于增强缺陷波场的波数滤波技术的比较。在 60 × 60 cm 的钢板上开出 1 mm 到 40 mm 各种直径的半厚孔。第二块板具有非方形几何形状，数据具有多路径反射。使用这两个数据集，我们在没有明确实验基线的情况下隔离了损伤反射。我们还简要说明了我们的字典学习方法与通常用于增强缺陷波场的波数滤波技术的比较。