Phased array ultrasound is a widely used technique in non-destructive testing. Using piezoelectric elements as both sources and receivers provides a significant gain in information and enables more accurate defect detection. When all source-receiver combinations are used, the process is called full matrix capture. The total focusing method~(TFM), which exploits such datasets, relies on a delay and sum algorithm to sum up the signals on a pixel grid. However, TFM only uses the first arriving p-waves, making it challenging to size complex-shaped defects. By contrast, more advanced methods such as reverse time migration~(RTM) and full waveform inversion~(FWI) use full waveforms to reconstruct defects. Both methods compare measured signals with ultrasound simulations. While RTM identifies defects by convolving forward and backward wavefields once, FWI iteratively updates material models to reconstruct the actual distribution of material properties. This study compares TFM, RTM, and FWI for six specimens featuring circular defects or Y-shaped notches. The reconstructed results are first evaluated qualitatively using different thresholds and then quantitatively using metrics such as AUPRC, AUROC, and F1-score. The results show that FWI performs best in most cases, both qualitatively and quantitatively.

翻译：相控阵超声是无损检测中广泛应用的技术。使用压电元件同时作为发射源和接收器可显著提升信息获取量，从而实现更精确的缺陷检测。当使用所有发射-接收组合时，该过程称为全矩阵采集。利用此类数据集的全聚焦法（TFM）基于延迟叠加算法，在像素网格上对信号进行叠加。然而，TFM仅利用首达P波，这使得复杂形状缺陷的尺寸评估面临挑战。相比之下，逆时偏移（RTM）和全波形反演（FWI）等更先进的方法利用全波形数据进行缺陷重建。这两种方法均通过测量信号与超声模拟结果的对比实现缺陷检测：RTM通过一次正演与反演波场卷积识别缺陷，而FWI通过迭代更新材料模型来重建材料属性的实际分布。本研究针对含圆形缺陷或Y形切口的六个试样，对比了TFM、RTM和FWI的成像性能。重建结果首先通过不同阈值进行定性评估，继而采用AUPRC、AUROC和F1分数等指标进行定量分析。结果表明，在多数情况下FWI在定性与定量评估中均表现最优。