车载探地雷达回波信号增强技术的研究

发布时间：2018-06-27 12:40

本文选题：车载探地雷达 + 回波信号增强　；参考：《西南交通大学》2016年硕士论文

【摘要】：我国铁路隧道和高速铁路隧道已经位于世界首位,铁路隧道的病害普查和定期健康状态检查,急需一种无接触式的快速无损检测手段。探地雷达无损检测技术广泛于隧道质量与病害检测,但是由于目前普遍使用地面耦合天线,不具备快速检测条件。为了能在列车正常运行条件下检测隧道,我国研究了具有快速检测特点的车载探地雷达隧道检测系统。该系统采用空气耦合天线,天线安装在车辆限界以内。由于天线离隧道壁距离增大,导致深层反射回波信号减弱。本文针对这一问题,开展深层反射回波信号增强技术的研究,为我国高速铁路隧道车载探地雷达检测技术提供技术支持,具有重要的意义。目前深层反射回波信号增强主要在雷达数据后处理软件中实现,这种方法没有增强有用信号,虽然可以抑制部分系统噪声,但对信噪比的提高十分有限。为了克服现有方法的缺点,本文的研究是在接收天线之后、取样头之前采用硬件对回波信号进行时变增益放大,它只放大回波有用信号,而对系统噪声不做任何放大,从而提高了信噪比,同时补偿了因天线离隧道壁距离增大而造成的扩散损失。本文在电磁波传播理论基础上,分析了电磁波的衰减机理,并得出球面指数补偿(SEC)增益为依据的增益补偿方法。由于目前使用的车载探地雷达隧道检测系统采用等效采样原理,因此本文着重分析了接收系统的回波信号等效采样方法和电路,包括该方法的理论分析,采样保持、数模转换。在等效采样理论和现有硬件条件下,首次提出了“等效时变增益放大”概念,根据“等效时变增益放大”概念,设计和制作了时变增益放大电路,经过多次改进,达到了对回波信号时变增益放大目标。试验结果表明,本文设计的时变增益(TVG)放大电路,最大增益可以到达13分贝,可以补偿2.5米的几何衰减。采用本文的研究成果,天线与隧道壁最大距离可增加到4.75米,能够满足我国高铁双线隧道单边检测的要求,具有实用意义。
[Abstract]:China's railway tunnel and high-speed railway tunnel have been ranked first in the world. The disease survey and periodic health condition inspection of railway tunnel are in urgent need of a non-contact rapid nondestructive testing method. Ground penetrating radar (GPR) nondestructive testing technology is widely used in tunnel quality and disease detection, but the ground coupled antenna is widely used at present, so it is not suitable for rapid detection. In order to detect the tunnel under the normal running condition of the train, the tunnel detection system of on-board ground penetrating radar (GPR) with the characteristics of fast detection has been studied in China. The air-coupled antenna is used in the system, and the antenna is installed within the vehicle limit. The deep reflection echo signal is weakened due to the increase of antenna distance from tunnel wall. In order to solve this problem, the research of deep reflection echo enhancement technology is carried out in this paper, which provides technical support for the detection technology of on-board ground penetrating radar in high-speed railway tunnels in China, which is of great significance. At present, the deep reflection echo signal enhancement is mainly realized in the radar data post-processing software. This method does not enhance the useful signal, although it can suppress part of the system noise, but the improvement of signal-to-noise ratio is very limited. In order to overcome the shortcomings of the existing methods, the research in this paper is that after receiving the antenna, the sampling head uses hardware to amplify the echo signal with time-varying gain, which only amplifies the useful echo signal, but does not amplify the system noise. Thus the signal-to-noise ratio (SNR) is improved and the diffusion loss caused by the increase of the antenna distance from the tunnel wall is compensated. Based on the theory of electromagnetic wave propagation, the attenuation mechanism of electromagnetic wave is analyzed, and the gain compensation method based on spherical exponent compensation (SEC) is obtained. Due to the principle of equivalent sampling used in the current vehicle GPR tunnel detection system, this paper focuses on the analysis of the equivalent sampling method and circuit of the echo signal of the receiving system, including the theoretical analysis of the method, the sampling and holding, and the digital-analog conversion. Under the condition of equivalent sampling theory and existing hardware, the concept of "equivalent time-varying gain amplification" is proposed for the first time. According to the concept of "equivalent time-varying gain amplification", a time-varying gain amplifier circuit is designed and fabricated. The target of time-varying gain amplification of echo signal is achieved. The experimental results show that the maximum gain can reach 13 decibels and the geometric attenuation of 2.5 meters can be compensated by the time-varying gain (TVG) amplifier designed in this paper. The maximum distance between the antenna and the tunnel wall can be increased to 4.75 m, which can meet the requirement of one-sided detection of the double-line tunnel of high-speed rail in China, and it is of practical significance.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U457.4

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