Chen Mu, Xu Xintao, Yang Keji, Wu Haiteng
The State Key Laboratory of Fluid Power and Mechatronic Systems, College of Mechanical Engineering, Zhejiang University, Hangzhou 310027, China.
Hangzhou Shenhao Technology Co., Ltd., Hangzhou 311121, China.
Sensors (Basel). 2024 Jan 27;24(3):832. doi: 10.3390/s24030832.
The total focusing method (TFM) has been increasingly applied to weld inspection given its high image quality and defect sensitivity. Oblique incidence is widely used to steer the beam effectively, considering the defect orientation and structural complexity of welded structures. However, the conventional TFM based on the delay-and-sum (DAS) principle is time-consuming, especially for oblique incidence. In this paper, a fast full-matrix imaging algorithm in the Fourier domain is proposed to accelerate the TFM under the condition of oblique incidence. The algorithm adopts the Chebyshev polynomials of the second kind to directly expand the Fourier extrapolator with lateral sound velocity variation. The direct expansion maintains image accuracy and resolution in wide-angle situations, covering both small and large angles, making it highly suitable for weld inspection. Simulations prove that the third-order Chebyshev expansion is required to achieve image accuracy equivalent to the TFM with wide-angle incidence. Experiments verify the algorithm's performance for weld flaws using the proposed method with the transverse wave and the full-skip mode. The depth deviation is within 0.53 mm, and the sizing error is below 15%. The imaging efficiency is improved by a factor of up to 8 compared to conventional TFM. We conclude that the proposed method is applicable to high-speed weld inspection with various oblique incidence angles.
全聚焦方法（TFM）因其高图像质量和缺陷敏感性，在焊缝检测中得到了越来越广泛的应用。考虑到焊接结构的缺陷方向和结构复杂性，斜入射被广泛用于有效地控制波束。然而，基于延迟求和（DAS）原理的传统TFM耗时较长，尤其是在斜入射情况下。本文提出了一种傅里叶域快速全矩阵成像算法，以加速斜入射条件下的TFM。该算法采用第二类切比雪夫多项式直接展开横向声速变化的傅里叶外推器。直接展开在广角情况下保持了图像的准确性和分辨率，涵盖了小角度和大角度，非常适合焊缝检测。仿真证明，需要三阶切比雪夫展开才能实现与广角入射TFM相当的图像精度。实验使用横波和全跳模式验证了该算法对焊缝缺陷的检测性能。深度偏差在0.53mm以内，尺寸误差在15%以下。与传统TFM相比，成像效率提高了8倍。我们得出结论，该方法适用于各种斜入射角的高速焊缝检测。
