面向非规则界面双层介质超声全聚焦成像

Ultrasonic total focusing method for double-layer media with irregular interface

为解决盲测工况下双层介质全聚焦成像困难的问题,提出了一种基于虚拟源(VS)的全聚焦(TFM)成像技术。首先,利用全矩阵数据集中的对角线信号一次界面回波飞行时间,在非规则双层介质界面建立一系列虚拟源点。通过对虚拟源点插值或拟合处理得到实现非规则介质界面的重建。最后,通过重构的界面寻找可能的折射点,以满足盲测条件下非规则界面双层介质TFM的成像条件。盲测条件下的结果表明,VS-TFM图像中的非规则界面和缺陷位置与实际吻合。与基于虚拟源的合成孔径聚焦技术(SAFT)相比,对于凸面试块,VS-TFM图像的信噪比提升了4.66~13.31 dB;对于凹面试块,VS-TFM图像的信噪比提升了4.74~12.8 dB,且API值基本相同,成像时间几乎不增加。因此,本文所提方法将全聚焦成像的应用对象拓展至盲测工况下非规则双层介质。

To solve the problem of total focusing imaging of double-layer media under blind measurement conditions,this article proposes a total focusing method(TFM)based on virtual source(VS).Firstly,a series of virtual sources are established on the irregular interface of the double-layer media by using the first echo time-of-flight of the diagonal signals of full matrix capture data.Then,the irregular interface of the double-layer media is reconstructed by interpolating or fitting the virtual sources on the interface.Finally,the reconstructed interface is used for possible refraction points to achieve the TFM imaging condition for the irregular interface of double-layer media.The results show that the position of the surface and flaws are both located correctly in TFM images under blind measurement conditions.Compared with the synthetic aperture focusing technique(SAFT)imaging technology based on virtual source(VS),the signal-to-noise ratio of the VS-TFM images is improved by 4.66~13.31 dB in the convex specimen,and by 4.74~12.8 dB in the concave specimen,with nearly the same API values and minimal increase in imaging time.Therefore,the proposed method extends TFM imaging to double-layer media with irregular surfaces in blind measurement conditions.