Wang Gonglin, Xu Caibin, Lai Quanqing, Deng Mingxi
College of Aerospace Engineering, Chongqing University, Chongqing 400044, China.
College of Aerospace Engineering, Chongqing University, Chongqing 400044, China.
Ultrasonics. 2025 Nov;155:107703. doi: 10.1016/j.ultras.2025.107703. Epub 2025 May 25.
When an ultrasound tone-burst propagates in an elastic solid with quadratic nonlinearities, a pulse wave with a carrier frequency of zero (referred to as zero-frequency wave, ZFW) will be generated due to material nonlinearity. The low acoustic attenuation characteristics of ZFW is particularly well-suited for defect detection of highly attenuative materials. In our previous study, large detection depths in high-density polyethylene (HDPE) have been demonstrated using ZFW. However, in practical engineering applications, defect detection in HDPE with irregular surfaces is hindered by limitations in complex propagation path and low coupling efficiency. To address this issue, using ZFWs generated by the propagation of high-frequency ultrasonic waves, a water immersion SAFT imaging method is proposed for HDPE with irregular surfaces. The proposed method, based on the priori knowledge of geometric interface between water and the measured HDPE with irregular surface, utilizes the Snell's law to get the propagation paths of the ZFWs. The propagation time of ZFW in water and HDPE is computed using these paths, through which its time-of-flight is obtained. The time-of-flight is subsequently utilized to calculate the intensity of each pixel. Finally, the normalized imaging results are finally generated after iterative computations across all scanning points. Experimental results show that the proposed method is capable of detecting side-drilled hole defects with a diameter of 1 mm and a longitudinal depth of approximately 100 mm in HDPE with irregular surfaces including incline surface, convex surface, and concave surface. These findings validate the effectiveness of the proposed method in detecting defects in highly attenuative materials with irregular surface, demonstrating its potential as a valuable tool for non-destructive testing.
当超声短脉冲串在具有二次非线性的弹性固体中传播时，由于材料非线性，会产生载波频率为零的脉冲波（称为零频率波，ZFW）。ZFW的低声衰减特性特别适合于高衰减材料的缺陷检测。在我们之前的研究中，已证明使用ZFW可在高密度聚乙烯（HDPE）中实现较大的检测深度。然而，在实际工程应用中，HDPE表面不规则时的缺陷检测受到复杂传播路径和低耦合效率的限制。为了解决这个问题，利用高频超声波传播产生的ZFW，提出了一种用于表面不规则的HDPE的水浸SAFT成像方法。该方法基于水与表面不规则的被测HDPE之间几何界面的先验知识，利用斯涅尔定律获取ZFW的传播路径。利用这些路径计算ZFW在水和HDPE中的传播时间，从而得到其飞行时间。随后利用飞行时间计算每个像素的强度。最后，在对所有扫描点进行迭代计算后，最终生成归一化成像结果。实验结果表明，该方法能够检测表面不规则（包括倾斜表面、凸表面和凹表面）的HDPE中直径为1mm、纵向深度约为100mm的侧钻孔缺陷。这些发现验证了该方法在检测表面不规则的高衰减材料中的缺陷方面的有效性，证明了其作为无损检测有价值工具的潜力。
