超声显微成像中寄生信号构成机理与处置技术研究

The experimental investigation is focused on the objectives – acoustic lens of an acoustic microscope and its acoustical behavior – including a process which a series of accompanied derivant acoustic wave (signal) take place, as acoustic lens pulsed by an excitation to produce a focused ultrasound beam, and a relevant process the negative influence on acoustical imaging. Under the converse piezoelectric effects, all kinds of wave received by acoustic lens are transformed into a series of electric signals continuously distributed in echo signal pattern, participating in acoustical imaging process (A-, B- and C-Scan). The internal acoustic interactions and derivant processes, which are hidden or exposed inside results of various acoustical imaging through the media of the electric signals: it becomes difficult to measure accurate time interval information, for the reason of a real signal is mixed or covered by a parasitical signal in A-Scan; the real image of an internal micro structure is coved by a distortion image caused by a parasitic signal; and even some lamellar image (C-Scan) lose completely. All these influences are seriously harmful to acoustical imaging, evaluation and characterization. It becomes a miserable works for imaging characterization. Based on the investigation on the formation of parasitic signals, and the way it participates the imaging processes, try to obtain all physics resource inside the waveguide of acoustic lens and its mathematical model theoretically, to enrich and optimize the theory of acoustic microscopy; furthermore, to explore a set of new techniques and skills to overcome or reduce the negative influence of the parasitical signals; and to provide a new and powerful technology for the applications of scanning acoustic microscopy working for the evaluation and characterization in internal structure of a solid materials.

课题以声学显微镜超声镜头及其声学行为为研究对象，对其激励产生聚焦声波时伴生衍生声波，及其对显微成像施加负面影响的过程，进行系统实验研究。镜头产生的各类声波最终经逆压电效应，转换为连续分布的电声信号并参与到A-、B-和C-Scan成像。其内部声学交互作用和衍生过程由信号这个介质隐藏或显露在各种成像结果中:A-Scan图像发生寄生信号与有用信号的交叠，使信号的时间信息测量变得困难；B-Scan图像因寄生信号导致的畸形成像，与材料内部结构形成影像叠加覆盖；部分C-Scan层状图像完全缺失等，对超声显微成像、分析与表征构成极大危害，使图像分析表征工作苦不堪言。通过对隐藏的寄生信号其自身构成规律，以及其参与成像过程的规律研究，从理论上找出其物理源头及模型，完善丰富超声显微学理论，进而探索一套规避寄生信号的处置技术和新工艺，为超声显微成像更好应用于固体材料内部结构成像的研究与表征，提供更有效的新方法。

本课题对超短脉冲扫描超声显微镜系统的核心器件---聚焦超声镜头的寄生超声波及其电信号的物理机理，该寄生信号对材料结构成像过程中所表现出来的规律和作用，以及该行为对声成像和表征的负面影响进行系统的实验研究，试图从源头上找到导致超声寄生信号的来源，并以此找到优化超声镜头的设计和工艺的技术途径。.课题研究从超短脉冲电信号对圆盘型换能器的激励，产生超短脉冲的机械超声波，该超声波在超声镜头传导棒中的传播行为，重点是研究该超声波在镜头内部与传导棒的各个界面的声学交互行为进行理论梳理和实验验证，以及最终确定这些寄生信号在声成像几种模式上对应的作用规律等。.通过上述各层面的深入研究，明确了造成超声寄生信号的根本原因，本质上来自超声镜头顶部圆盘形换能器的环形边界，与棒体材料界面之间的声学交互行为，除了产生平面超声波以外，环形边界上所有点状声波源产生声波散射和衍射现象并产生积分效应，该具有积分效应的散射波再辐射出去，与超声镜头棒体的各个边界进行声学交互，同时还进行波的不同类型的变换，最终叠加成复杂的声波序列，并通过超声镜头的聚焦空穴辐射出去，作用到被测材料微观结构上，最终反射并被采集所表现出背底寄生声波的现象。实验研究表明，超短脉冲波束产生的波的形式，除了平面波外，还伴随镜头内部的声波的散射和衍射，在被收集的电信号的时间和空间上，表现出“挥之不去”寄生背景信号，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。.本课题从机理上揭示了超声镜头内部由于圆盘形换能器与棒体之间的声波交互作用，散射和衍射现象是不可忽略的因素，探明了其在几类超声成像模式上的表现形态及规律，从而探索出可否或减少寄生声信号的物理模型，同时如何研判标定寄生信号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。通过本课题的研究，从理论和技术工艺上丰富和发展了超声显微成像学及其新应用技术。