多盲孔缺陷的超声兰姆波时域拓扑能量成像方法研究

A study of the time-domain topology energy based ultrasonic Lamb wave imaging method for multi-blind hole defects

传统超声成像方法受瑞利准则的约束,难以对缺陷间距小于成像分辨率阈值的多缺陷进行成像。提出了一种基于时域拓扑能量的超声兰姆波成像方法,将逆散射拓扑成像方法中的拓扑渐进过程转换成求解直接声场和伴随声场。然后通过将伴随声场进行时间反转,两个声场将具有在缺陷处聚焦,在非缺陷处不聚焦的特性。将直接声场和伴随声场进行融合,以时域拓扑能量值作为像素值进行成像,从而使表征缺陷的精度较高。建立了缺陷间距小于分辨率阈值的多盲孔缺陷有限元模型,通过"一发多收"的方式激发S0模式和采集缺陷散射信号,并进行时域拓扑能量成像。仿真结果表明:对于多盲孔缺陷,时域拓扑能量成像法能够获得比延时叠加法和时间反转成像法更高的分辨率,并且能在缺陷间距小于成像分辨率阈值时进行成像。

The traditional ultrasonic imaging methods are constrained by Rayleigh criterion, so it is difficult to image multiple defects in the case of defect spacing less than the imaging resolution threshold. In this paper, an ultrasonic Lamb wave imaging method based on time-domain topological energy is proposed, which converted the topological gradual process in the inverse scattering topological imaging method into solving the forward sound field and the adjoint sound field. Then, the two sound fields, in which the adjoint sound field is time reversed, have the characteristics of focusing at the defects rather than focusing in the non-defective area. By fusing the forward sound field and the adjoint sound field and using the time-domain topological energy value as the pixel value for imaging, the defect can be characterized with high precision. In this paper, the finite element models of multi-blind hole defects in the case of defect spacing less than the imaging resolution threshold is established. The S0 mode Lamb wave is excited and the defect scattering signals are collected in the way of "one transmitter and multiple receiver" for time-domain topological energy imaging. The simulation results show that for multi-blind hole defects, the time domain topological energy imaging(TDTE) method can obtain higher resolution than the delay and sum(DAS) method and the time reversal(TR) imaging method, overcome the influence of mode conversion and achieve high-resolution imaging in the case of the defect spacing less than the imaging resolution threshold.