超声时间反转法自适应聚焦和目标检测
文献类型：学位论文
| 作者 | 魏炜 |
| 学位类别 | 博士 |
| 答辩日期 | 1999 |
| 授予单位 | 中国科学院声学研究所 |
| 授予地点 | 中国科学院声学研究所 |
| 关键词 | 时间反转法 超声自适应聚焦和检测 聚焦增益 聚焦波束 |
| 中文摘要 | 时间反转法是一种具有独特优点的自适应聚焦方法，不论介质和换能器阵列状况如何，在不需要它们的先验知识的情况下，可实现自适应聚焦。本文是针对现实的时间反转镜（即阵元是有限数目和有限宽度的换能器阵列）的自适应聚焦和检测，作理论和实验研究。理论上采用远场近似，直接在时域上得到简明的解析解，实验是采用我们研制的实验系统进行。我们主要研究聚焦束的特性，即聚焦增益和聚焦束的横向分辨率（束宽）。本文首先就均匀介质中时间反转法的聚焦过程在不同目标位置、不同阵列孔径、不同阵元数目等情况下的聚焦性能进行理论分析和实验研究，定量比较两者结果是相符的。因此这种分析方法可以作为实际的时间反转镜系统分析和设计的物理基础和依据。对于分界面是平行的或者是倾斜的分层介质，从理论上给出时间反转前后声扬的解析表达式。实验和理论分析都可见，当存在界面时，无须知道界面形状的任何知识，均可以实现自适应聚焦，它充分证明时间反转法是自适应聚焦的一个有力方法。与流体介质不同，固体中的激发将同时产生纵波和横波。理论分析和实验证明，时间反转法可以让纵波和横波同时聚焦。用紧贴固体表面的换能器阵列作时间反转镜，在平表面和弯曲表面进行的时间反转自聚焦实验，其结果与结论分析所得结果一般地符合较好。这也表明无论换能器状况如何它都能实现自适应聚焦。最后，本文还能超声检测中经常遇到的问题，即界面与目标区分问题，提出了用时间反转换元接收法进行目标区分，特别是它能判定反射信号是来自目标还是来自界面，这在实用上有较大的潜在价值。 |
| 英文摘要 | Ultrasonic time reversal (TR) is such a unique technique that it can realize self-adaptive focusing without the prior knowledge of the media and the transducer array. In this paper, we carried the theoretical and experimental research of self-focusing and testing performance, including the focusing gain and resolution of the focused beams, for the practical time reversal mirror(TRM) (that is to say, the transducer array which composed of the finite number of elements with finite width). The theoretical results are obtained directly in the time domain while the experiments are carried using the TRM system established in our laboratory. First, the TR focusing performance, under different target positions, different transducer array apertures, and different number of the elements, are researched. Quantitative comparison of theoretical results and the experiment ones show that they coincide with each other. So this method of analysis can be used as the physical basis to design and analyze the TMR system. As for the layered medium whose interface is parallel or slant, the experiments and the theoretical analyses show that the self-focusing can be realized without any knowledge of the interface condition. This proves adequately that TR is a powerful method to realize self-focusing. Different without the fluid, there are two kinds of wave generated in the solid, viz. transverse wave and shear wave. The theoretical analysis and experiments show that TR can focus these two kinds of wave synchronously. Using the time reversal mirror located directly on the plane and curving surface, the TR experiment results show good coincidence with the theoretical ones. These also show that TR can realize the self -focusing In addition, aiming at the problem faced in ultrasonic TR self-adaptive testing viz. distinguishing the interface from the target, the method of changing the revceiver after TR is proposed to distinguish targets, especially it can be used to judge whether the signal is reflected from target or interface. This will be potentially useful in practice. |
| 语种 | 中文 |
| 公开日期 | 2011-05-07 |
| 页码 | 129 |
| 源URL | [http://159.226.59.140/handle/311008/614]  |
| 专题 | 声学研究所_声学所博硕士学位论文_1981-2009博硕士学位论文 |
| 推荐引用方式 GB/T 7714 | 魏炜. 超声时间反转法自适应聚焦和目标检测[D]. 中国科学院声学研究所. 中国科学院声学研究所. 1999. |
入库方式： OAI收割
来源：声学研究所
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