本文選題：車載探地雷達(dá) + 回波信號增強　； 參考：《西南交通大學(xué)》2016年碩士論文

【摘要】：我國鐵路隧道和高速鐵路隧道已經(jīng)位于世界首位,鐵路隧道的病害普查和定期健康狀態(tài)檢查,急需一種無接觸式的快速無損檢測手段。探地雷達(dá)無損檢測技術(shù)廣泛于隧道質(zhì)量與病害檢測,但是由于目前普遍使用地面耦合天線,不具備快速檢測條件。為了能在列車正常運行條件下檢測隧道,我國研究了具有快速檢測特點的車載探地雷達(dá)隧道檢測系統(tǒng)。該系統(tǒng)采用空氣耦合天線,天線安裝在車輛限界以內(nèi)。由于天線離隧道壁距離增大,導(dǎo)致深層反射回波信號減弱。本文針對這一問題,開展深層反射回波信號增強技術(shù)的研究,為我國高速鐵路隧道車載探地雷達(dá)檢測技術(shù)提供技術(shù)支持,具有重要的意義。目前深層反射回波信號增強主要在雷達(dá)數(shù)據(jù)后處理軟件中實現(xiàn),這種方法沒有增強有用信號,雖然可以抑制部分系統(tǒng)噪聲,但對信噪比的提高十分有限。為了克服現(xiàn)有方法的缺點,本文的研究是在接收天線之后、取樣頭之前采用硬件對回波信號進行時變增益放大,它只放大回波有用信號,而對系統(tǒng)噪聲不做任何放大,從而提高了信噪比,同時補償了因天線離隧道壁距離增大而造成的擴散損失。本文在電磁波傳播理論基礎(chǔ)上,分析了電磁波的衰減機理,并得出球面指數(shù)補償(SEC)增益為依據(jù)的增益補償方法。由于目前使用的車載探地雷達(dá)隧道檢測系統(tǒng)采用等效采樣原理,因此本文著重分析了接收系統(tǒng)的回波信號等效采樣方法和電路,包括該方法的理論分析,采樣保持、數(shù)模轉(zhuǎn)換。在等效采樣理論和現(xiàn)有硬件條件下,首次提出了“等效時變增益放大”概念,根據(jù)“等效時變增益放大”概念,設(shè)計和制作了時變增益放大電路,經(jīng)過多次改進,達(dá)到了對回波信號時變增益放大目標(biāo)。試驗結(jié)果表明,本文設(shè)計的時變增益(TVG)放大電路,最大增益可以到達(dá)13分貝,可以補償2.5米的幾何衰減。采用本文的研究成果,天線與隧道壁最大距離可增加到4.75米,能夠滿足我國高鐵雙線隧道單邊檢測的要求,具有實用意義。
[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.
【學(xué)位授予單位】：西南交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：U457.4

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