聚焦超声信号畸变机理及其声显微成像的应用研究

The study is based on the investigated object - focused ultrasound beam of acoustic microscope, starting from ultrasound signals structure and giving deep investigation on the distortion behavior of the acoustic aberrant signal, as a result of the longitudinal and transverse waves generated by the interaction between the focused ultrasound beam and material micro-structures. The core of the subject is to observe and investigate the micro-variation discipline of the reflected or transmitted ultrasound signals formation in the time axis and spatial scales, as the interaction process between the focused ultrasound waves and microstructure of material; To reveal the mechanism of intrinsic relation about various material microstructure and signal distortion; To cognize the discipline about the signal distortion manifestations in several types of acoustical imaging mode; Further, for distinguishing of the material (sub) micron-scale structural features in the two- and three-dimensional acoustical imaging, to provide a set of new analytical characterization method, proposing a signal synthesized analysis mode, which is based on the ultrasound signal distortion analysis and the time-resolved technique in acoustical imaging; To promote the accuracy of the analysis and improve the characterization of acoustic microscopy imaging. To propose a concept of ultrasound distortion signal for the first time and intends to establish a mathematical physics model of the ultrasound signal distortion mechanism, in order to explore a set of new technique can be applied to the field of acoustical imaging for material science and non-destructive testing/evaluation (NDT/E), enriching and optimizing the theory and skill of acoustic microscopy imaging, and developing new applications in the field of material science and high-precise mechanical techniques.

本课题以超短脉冲超声显微成像技术激励产生的脉冲聚焦波束为研究对象，针对该波束与材料微观结构交互作用过程中，其纵波、横波信号发生失真的畸变行为展开深入研究。研究的关键在于观测和探究其交互作用时，来自材料内部微观结构的反射或透射原因，造成超声信号在时序及空间构成上微观变化现象，从机理上揭示材料各种微观结构形态与信号畸变的内在联系；探究此类信号畸变在几类超声成像模式里的表现形态及规律；继而对材料内部(亚)微米尺度的结构元素在二维和三维声成像上的甄别，提出一套基于"声信号畸变"方法，与超声成像"时间处置"技术相统一的信号综合分析法，提高超声显微成像技术对块材内部微观结构分析表征的准确度。本课题首次提出超声信号畸变的现象并研究建立超声信号畸变机理的数理模型，丰富和完善超声显微成像理论,探索开发一套用于微观结构的无损检测与评估新表征方法，拓展在材料学科研究和高精密机械工艺等领域的新应用。

本课题对基于超短脉冲技术的扫描超声显微镜系统，对材料内部结构进行成像过程中出现超声信号畸变行为，以及该行为对声成像和表征的负面影响进行系统研究，试图从源头上找到导致超声信号畸变的原由，以探明该行为及其导致表征失实的机理，为可能的优化途径寻找理论依据。. 课题围绕超声成像系统的相关技术环节展开，对所有潜在要素进行系统的技术梳理和实验研究，涵盖了短脉冲声波在超声镜头内传导棒中的传播行为，重点对镜头外部声学行为，即激励声波与样品内部结构声学交互过程，以及超声畸变在声成像几种模式上对应规律几方面展开。. 通过上述各层面的深入研究，排除了畸变行为来自系统的干扰因素和超声镜头内部的声学交互过程，明确了造成超声信号畸变的根本原因本质上恰恰是镜头外部的声学交互行为，即来自聚焦激励声波对被测材料微观结构进行声学激励的交互过程，由此产生的声波衍生行为：超短脉冲聚焦波束与材料内部不同形态(缺陷、孔穴、内含物等)的微米尺度结构元素之间的交互，应运产生声学散射和衍射现象，衍生出反射声波在时间和空间上差异，被超声镜头聚焦孔径捕获后转换为超声电信号，出现叠加复合行为所表现出的信号畸变，在一维A超声信号序列图上、二维超声成像模式上(纵向侧切二维B超和不同深度水平横切二维C超图像)分别表现为信号的叠加、曲线扬起和成像模糊化等消极结果，就此揭开了超声信号畸变的“谜底”。. 本课题从机理上揭示了聚焦声波与材料微观结构形态之间声学交互作用与信号畸变的内在联系，探明了其在几类超声成像模式上的表现形态及规律，给出了基于声信号畸变判定方法和成像上的表征方法，提高利用超声显微镜技术对块材内部微观结构分析表征的准确度。课题的另一重要衍生成果是提出Square Column条块分割模型和基于isosurface等值面技术，在扫描超声显微镜技术领域实现了三维超声成像技术，探索开发出基于信号畸变综合分析表征方法和三维超声成像原型技术，丰富和发展了超声显微成像学及其新应用技术。