多缺陷兰姆波拓扑成像

将时间反转理论与拓扑优化思想结合在一起，引入了直接声场和伴随声场的概念。通过将时间反转后的兰姆波散射信号作为伴随声场中的二次激励源，实现了信号在缺陷处的聚焦，并根据时域拓扑能量公式计算出检测区域内各点的拓扑能量值，从而对薄板内多缺陷进行表征。有限元仿真和实验表明：在多缺陷情形下，延迟叠加法（Delay and Sum，DAS）因受瑞利准则的约束而在缺陷间距小于分辨率阈值时，无法对缺陷位置进行定位；时域拓扑能量法通过兰姆波时间反转聚焦、图像融合，不仅提高了缺陷检测分辨率，还消除了多模式、有噪声环境下伪像的干扰。有效推动了兰姆波在板类结构无损检测中的应用。

Multi-defect Lamb wave topological imaging

This paper combines time reversal theory with topology optimization ideas and introduces the concept of forward acoustic field and adjoint acoustic field. The time-inverted Lamb wave scattering signal is used as the secondary excitation source in the adjoint acoustic field, and the signal is focused at the defect. Then, the topological energy value of each point in the detection area is calculated according to the time domain topological energy formula. As a result, multiple defects in the sheet are characterized. Finite element simulations and experiments show that in the case of multiple defects, the delay-and-sum (DAS) method is unable to locate the defect when the defect spacing is smaller than the resolution threshold because of the constraints of the Rayleigh criterion; however, through Lamb wave time reversal focusing and image fusion, the time domain topological energy method can not only improve the defect detection resolution, but also eliminate the interference of artifacts in a multi-mode noisy environment. Lamb wave is effectively promoted in nondestructive testing of board structures.