中文摘要：

本文提出虚拟源与合成孔径技术相结合的成像方法来实现对双层结构的内部缺陷成像。通过相控阵探头延时聚焦的方法在界面形成虚拟声源，并对有机玻璃/钢双层结构中的聚焦声场进行了仿真，结果显示聚焦声束穿过界面后形成扩散球面波，适合采用合成孔径聚焦技术成像。实验中采用128阵元探头对含有横穿孔缺陷的有机玻璃/钢样品进行测量和波形采集，应用自适应滤波方法抑制界面回波，最后对波形使用合成孔径聚焦成像，得到的图像比B扫描成像具有较高的信噪比和横向分辨率，并且分辨率不随深度变化。

英文摘要：

We propose a new imaging method of double layer solid structure based on virtual source combined with SAFT(Synthetic aperture focusing technique).Ultrasound emitted from a phased array was focused at the interface and considered as the virtual source which detected deeper layer.In this paper,stress fields in plexiglas/steel structure are simulated by finite element method.The results show that wave front of transmitted wave is spherical which is very suitable for SAFT.Experiments were performed on plexiglas/steel with sided-hole defects on phased array system which excited focused ultrasound and transferred recorded data to PC.Then,the SAFT was applied on filtered wave data to obtain the image.The experimental results demonstrate that proposed method are superior to traditional B-scan imaging mode in both image quality and resolution.