超声相控阵动态聚焦技术研究

发布时间：2018-04-02 05:18

本文选题：超声相控阵　切入点：动态聚焦　出处：《西南交通大学》2014年硕士论文

【摘要】：超声相控阵通过控制相控阵探头的延迟时间来实现声束偏转、聚焦,从而实现对工件进行快速高效的检测。超声相控阵系统中的关键技术是指通过对发射和接收声束的时间和空间的有效控制,来获得高质量的声束和声场。相控阵数字技术有相位延迟技术、动态聚焦技术、动态变迹技术、动态孔径技术和编码发射技术等研究方向,其中动态聚焦技术是比较重要的一项。动态聚焦技术能够提高焦点的焦区深度,减小焦点宽度,从而提高声束的一致性和空间分辨率,为缺陷的检测提供了更为可靠的依据。本文重点研究了超声相控阵聚焦技术的原理以及影响相控阵聚焦精度和分辨率的因素,提出了改善常规聚焦声束分辨率的方法和相控阵动态聚焦压缩存储算法,验证了动态聚焦技术在提高空间分辨率和成像一致性上的优越性。本文进行了以下方面的研究： 1、论述了超声相控阵检测相关原理,如换能器的声场辐射原理、相控阵进行无损检测时的声束控制原理。基于阵列换能器的辐射原理对一维相控阵换能器的声场建模,并系统的研究了换能器参数对聚焦声束的影响,通过对不同的阵元数、阵元间距等的聚焦声束的特性进行对比,建立了提高超声相控阵动态聚焦成像质量的参数选取依据。 2、讨论了延时精度对聚焦效果的影响,通过分析可知,在换能器阵列的参数已定的前提下,延时精度是影响动态聚焦声束的重要因素。对缺陷进行了仿真实验,通过实验可知,动态聚焦对成像质量有大幅度改善。 3、提出了一种基于超声相控阵聚焦延时参数的压缩存储方式。这种方法分三步：第一,将聚焦延时参数换算成相邻阵元之间的相对延时参数,然后取量化值；第二,分别存储相对延时参数的初始值和延时值发生变化的位置,以此完成了压缩存储；第三,在实现动态聚焦的过程中,将压缩存储的延时量进行实时解压,并将生成的延时参数传给换能器。结果验证：此方法可再保证聚焦声束质量的前提下大大减小延时参数所占内存。 4、基于FPGA设计了超声相控阵高精度发射模块,本文通过PLL(锁相环)的倍频和移相技术代替了外部的延迟线,从而使电路结构得到简化,使粗延时和细延时的实现在一块电路板上完成,在提高延时精度的前提下,解决了板间不同步的问题。
[Abstract]:Ultrasonic phased array can realize beam deflection and focus by controlling the delay time of phased array probe, so that the work piece can be detected quickly and efficiently.The key technology of ultrasonic phased array system is to obtain high quality sound beam and sound field by controlling the time and space of transmitting and receiving sound beam effectively.Phased-array digital technology includes phase delay technology, dynamic focusing technology, dynamic apodization technology, dynamic aperture technology and coded emission technology, among which dynamic focusing technology is an important one.The dynamic focusing technique can improve the focal depth and decrease the focus width, thus improving the consistency and spatial resolution of the sound beam, which provides a more reliable basis for defect detection.This paper focuses on the principle of ultrasonic phased array focusing technology and the factors that affect the accuracy and resolution of phased array focusing. A method to improve the conventional focusing sound beam resolution and a dynamic focusing compression storage algorithm for phased array are proposed.The advantages of dynamic focusing technique in improving spatial resolution and imaging consistency are verified.In this paper, the following aspects of the research:1. The related principles of ultrasonic phased array detection, such as the sound field radiation principle of transducer and the sound beam control principle of phased array nondestructive testing, are discussed.Based on the radiation principle of array transducer, the sound field of one-dimensional phased array transducer is modeled, and the influence of transducer parameters on focused sound beam is systematically studied.The parameter selection basis for improving the quality of ultrasonic phased array dynamic focusing imaging is established.2. The effect of delay precision on focusing effect is discussed. Through analysis, it is known that delay precision is an important factor affecting dynamic focusing sound beam on the premise that the parameters of transducer array have been determined.The simulation results show that dynamic focusing can improve the imaging quality greatly.3. A compression storage method based on ultrasonic phased array focusing delay parameters is proposed.This method is divided into three steps: first, the focusing delay parameters are converted into the relative delay parameters between adjacent array elements, and then the quantization values are taken; second, the initial values of the relative delay parameters and the positions where the delay values change are stored respectively.In the process of dynamic focusing, the time delay of the compressed storage is decompressed in real time, and the generated delay parameters are transmitted to the transducer.The results show that this method can greatly reduce the memory occupied by delay parameters on the premise of focusing sound beam quality.4. Based on FPGA, the high precision transmission module of ultrasonic phased array is designed. In this paper, the frequency doubling and phase shifting technology of PLL (PLL) are used to replace the external delay lines, so the circuit structure is simplified.The realization of coarse delay and fine delay is completed on a single circuit board, and the problem of non-synchronization between boards is solved on the premise of improving delay precision.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB553

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