基于虚拟源的非规则双层介质频域合成孔径聚焦超声成像

Frequency domain synthetic aperture focusing technique for irregular two-layered medium based on visual source

为实现非规则双层介质的快速超声成像,提出一种基于虚拟源(VS)的频域合成孔径聚焦技术(SAFT)。首先,借助VS技术在未知界面几何形状的不规则双层介质的表面建立一系列虚拟源点。其次,对所建不均匀分布的虚拟源点进行插值处理,得到近似表征分层界面形状的数学表达式。然后,根据界面表达式,建立表征网格成像区域内速度分布的速度模型。最后,在非稳态相位迁移成像实施过程中,利用声速模型适应每个迁移步进位置上声速的水平变化。通过凸面和正弦曲面工件成像实验验证频域VS-SAFT的有效性,同时对比时、频域VS-SAFT的成像结果和运算效率。结果表明,2种VS-SAFT图像基本还原了缺陷位置和工件表面形状。单核测试条件下,频域VS-SAFT的计算时间仅为0. 47~0. 53 s,而时域VS-SAFT需要91. 21~93. 54 s。

To achieve high-speed ultrasonic imaging for irregular two-layered medium,one kind of frequency domain synthetic aperture focusing technique(SAFT)based on visual source(VS)technique is proposed.Firstly,VS technique is adopted to construct a series of VS points at the interface of an unknown testing object with irregular two-layered structure.Secondly,the expression of irregular interface is obtained by the interpolation processing with the coordination of VS points.Thirdly,the velocity model is formulated,which represents the velocity distribution in the mesh imaging region according to the expression.Finally,the velocity model is used to accommodate lateral velocity variation for each migration interval during the implementation process of the non-stationary phase shift migration imaging.The performance of the method is evaluated using the convex surface and the sinusoidal curve surface,respectively.Meanwhile,the imaging results and the operation efficiency of the frequency domain VS-SAFT are compared with the time domain VS-SAFT.Experimental results show that the defect location and the surface shape are displayed accurately in two kinds of VS-SAFT images.In the single CPU core condition,the calculation time is only 0.47~0.53 s for the frequency domain VS-SAFT.However,the time domain VSSAFT need consume 91.21~93.54 s.