磁感应断层成像技术中的相位差检测技术探究

发布时间：2018-01-22 15:57

本文关键词： 磁感应断层成像相位测量 DDS 锁相环鉴相器　出处：《云南师范大学》2017年硕士论文　论文类型：学位论文

【摘要】：磁感应断层成像技术(Magnetic Induction Tomography,MIT)依据涡流检测原理获得与目标物体电导率分布相关的信息,可用于机体组织水肿的非接触测量,受到医疗检测领域的广泛关注。MIT技术通过检测磁场的相位变化来检测出电导率,但由于生物组织的电导率太小,导致相位的高精度测量难度较大。目前比较常用的模拟相位差检测方法可分为时序法和乘法器电路法,但模拟器件的温度漂移会导致相位偏移较大。除了上述方法外,目前还有数字正交变换法、数字相关法等数字鉴相方法。数字相位检测方法相对比较灵活,但是实时性低且实现成本较高。根据MIT的技术特点,相位差检测系统的精度越低则成像质量越高,但是目前大部分的相位差检测系统精度普遍不够,如何高效精确地测量频率较高的磁场的相位变化成为了MIT技术的核心问题。本文研究了可用于MIT技术的几种相位差检测方法,并通过理论和实验对比各自的特性,所涉及的鉴相方法包括:乘法鉴相法、数字正交变换法、数字相关法、FFT谱分析法、AD8302法。研究中利用多通道DDS信号发生器产生相位差已知的两通道10MHz正弦信号,后端鉴相器相关实验则有两种不同的实现方法:对于数字鉴相法先将模拟信号采样转换为数字信号后使用各数字鉴相方法对信号的相位差进行检测;对于模拟鉴相法直接将两通道信号输入到模拟鉴相器中进行鉴相。通过对比各鉴相方法发现:傅里叶谱分析法具有较好的鉴相精度和较广鉴相范围(精度:±0.2°,范围:0-360°)。本文还分析并实现了基于锁相环器件实现的相位差检测方法,搭建了实际的实验系统,通过实验证明锁相环实现的鉴相精度能够达到0.2°(10MHz),相对于傅里叶变换法实时性较强,但由于电流泵的死区影响导致其鉴相范围较小。本文最后提出了基于DDS信号源和高、低精度鉴相器组合鉴相的主动移相鉴相法,并使用锁相环器件和AD8302实现了实际的主动移相鉴相实验系统的设计。通过实验测试发现,主动移相鉴相法可以避开鉴相器的非线性区域和低精度区,能够改善传统鉴相方法的鉴相范围和鉴相精度(精度:±0.2°,范围0-180°),具有一定的参考价值和应用前景。
[Abstract]:Magnetic Induction Tomography (mitt) is used to obtain the information related to the electrical conductivity distribution of the target object according to the principle of eddy current detection. It can be used for non-contact measurement of tissue edema. MIT technology has attracted wide attention in the field of medical detection. MIT technology detects electrical conductivity by detecting the phase change of magnetic field, but the electrical conductivity of biological tissue is too small. It is difficult to measure the phase with high precision. At present, the analog phase difference detection methods can be divided into sequential method and multiplier circuit method. In addition to the above methods, there are digital phase discrimination methods such as digital orthogonal transform method, digital correlation method and so on. The digital phase detection method is relatively flexible. According to the technical characteristics of MIT, the lower the accuracy of the phase difference detection system, the higher the imaging quality, but most of the current phase difference detection system is generally not accurate enough. How to measure the phase change of magnetic field with high frequency and high efficiency has become the core problem of MIT technology. This paper studies several phase difference detection methods which can be used in MIT technology. And through the theoretical and experimental comparison of their characteristics, the phase detection methods involved include: multiplication phase detection method, digital orthogonal transform method, digital correlation method FFT spectrum analysis. AD8302 method. The multi-channel DDS signal generator is used to generate two-channel 10MHz sinusoidal signal with known phase difference. There are two different methods in the experiment of back-end phase discriminator: firstly, the analog signal is sampled into digital signal by digital phase discriminator, and then the phase difference of the signal is detected by each digital phase discriminator method. For the analog phase detection method, the two-channel signal is directly input into the analog phase discriminator for phase detection. By comparing each phase detection method, it is found that the Fourier spectrum analysis method has better phase identification accuracy and wider phase detection range (. Accuracy: 卤0.2 掳. The detection method of phase difference based on PLL device is also analyzed and realized, and a practical experimental system is built. The experimental results show that the phase detection accuracy of the PLL can reach 0.2 掳/ 10MHz / L, which is better than the Fourier transform method. However, due to the influence of the dead zone of the current pump, the range of phase detection is small. Finally, an active phase shift phase detection method based on DDS signal source and combination of high and low precision phase discriminator is proposed. The practical active phase shift phase detection system is designed by using PLL device and AD8302. The experimental results show that the active phase shift method can avoid the nonlinear region and low precision area of the phase detector. It can improve the range and precision of the traditional phase detection method (accuracy: 卤0.2 掳, range 0-180 掳), which has certain reference value and application prospect.
【学位授予单位】：云南师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN763.3;TN911.8

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