【作者】 邹爱民；

【导师】 程德福；

【作者基本信息】 吉林大学 ， 测试计量技术及仪器， 2011， 博士

【摘要】 探地雷达是近十几年来发展起来的地球物理探测仪器,广泛应用于工程、环境等无损探测。目前取得良好应用效果的探地雷达系统均为超宽带脉冲体制,仪器设备主要依赖进口。本文以隧道地质预报这一应用为背景,开展了低频段脉冲探地雷达相关技术研究工作。给出了一种仪器总体设计方案,由超宽带收发天线、超宽带脉冲源模块、采集与控制模块、上位机等组成,实现了超宽带脉冲电磁波的产生、辐射、接收、数据采集、处理成像等功能。在超宽带脉冲产生方面,通过选择合适的雪崩三极管及电路结构实现了用较少数量的雪崩三极管产生较大幅度的纳秒级窄脉冲,这样的工作方式可增强雪崩电路的稳定性。基于此思想,设计了单级雪崩三极管串行级联电路。获得的纳秒级窄脉冲的幅度、频谱、重复频率等指标满足隧道地质预报对脉冲探地雷达的基本要求。脉冲源电路与应用于超宽带雷达系统中的脉冲源的对比结果表明,本文设计的脉冲源具有结构简单、性能稳定等优点。针对平面对称阵子类超宽带天线做了大量的研究工作,指出了平面蝶形天线在较高的频点上方向图变异问题,并与平面半椭圆天线做了对比,分析了其本质原因,指出了其最佳的脉冲辐射方向。提出了两种方法来实现超宽带脉冲源电路与平面蝶形天线系统的匹配:集总阻感加载方法和射频变压器匹配法。实测结果证明了这两种方法的有效性和实用性。为实现平面对称振子天线的定向辐射特性,对振子的边缘形状做了优化设计,并提出了屏蔽式四分之一椭圆天线(SQEA)的概念。仿真结果表明,此天线具有良好的阻抗带宽,时域脉冲辐射失真小,前后比可达35dB,能有效屏蔽非目标方向的辐射。超宽带脉冲通过空间辐射和电路系统的反射,对同步系统中的时钟信号形成了强烈的干扰,对此设计了基于光耦器件和瞬态抑制器件的干扰抑制电路,提高了系统同步精度。基于Windows环境,设计了上位机软件,实现了数据的实时采集、传输、处理、A-scan、B-scan显示成像、存储及系统控制等功能。更多还原

【Abstract】 As a geophysics exploration instrumentation with the highest resolution rising in the last decade, Ground penetrating radar (GPR) has been already widely used in the fields of construction,tunnel engineering,environment,archaeology and military for non-destructive testing.UWB pulse-GPR system is the most successful and has been proved in the practice as a useful geophysics exploration instrumentation.Instrument equipments of GPR system are mainly depended on import now. In order to ensure the safety of tunnel constructing and avoiding geological disaster,it is necessary to predict the geology in front of the tunnel face using scientific instruments.It is called Tunnel geology prediction(TGP).Tunnel seismic method associated with GPR method can accurately predict geology several ten meters in front of the tunnel face.This paper takes this application as background,and attempts to design and produce the low-resolution Pulse-GPR instrument equipments to meet the application requirement of tunnel geological prediction (TGP).The main research work of this paper are as follows:(1) The design of the low-resolution pulse GPR system.The instrument system consists of four parts:ultra-wideband(UWB) transceiver antennas,UWB pulser module, data acquisition module and the host computer.It achieves the assignment as followings:generation of UWB pulse, transmission and receival, data acquisition and imaging.(2) Design of the UWB pulser.UWB pulser is proposed to genetrate nanosecond time domain pulse.The principle of avalanche transistor and the basic circuit of avalanche transistor is analysed.Main methods of generating UWB pulse are compared with each other.Series-wise avalanche circuit and Marx circuit based on avalanche transistor are contrasted.Avalanche transistors that have high avalanche beakdown voltage and high cut-off frequency are elaborately selected and tested.Single stage series-wise avalanche circuit can achieve the proposed nanosecond time domain pulse and requires the least avalanche transistors.Single stage series-wise avalanche circuit is designed and applied in the UWB Pulse-GPR system as the UWB pulser.Testing results show that the pulse outputed by the pulser has several advantages such as high frequency stability,high waveform stability,high repetition frequency. This is necessary that the pulser can be used in the Pulse-GPR system. The amplitude and spectrum of the pulse are suitable in the pulse-GPR system for the application of TGP. The UWB pulser is compared with other pulser used in UWB radar system and they have respective advantages and disadvantages.The pulser designed in the paper has simple structure and stable performance.(3) Design and match methods of the planar bowtie antenna.UWB planar dipoles antennas are familiar in the UWB Pulse-GPR system and they are simulated and analysised by HFSS and CST software. Performance of plannar Bowtie antenna is given under different structure parameter.The paper investigated the split of radiation pattern when Bowtie antenna works on high frequence(compared to its structure).The substaintial reason is analysed.The problem astricted the bandwidth of the radiation pattern and decided the best radiation direction of the antenna.The extent of the split problem is decided by the equivalent degree in the side of the Bowtie antenna.In order to achieve the match between the antenna and the pulser a resistively-inductively loaded (RL-loaded) method for bowtie antenna is theoretically and experimentally investigated.The antenna has been designed for transmission of Gaussian-like pulses with duration of 5ns.The RL-loading method raised in this paper makes the UWB pulse generator and the antenna-feed system get matched fast in the laboratory.The time-domain waveforms and VSWR of the antenna are shown in this paper.RF transformer (JTX-2-10T+) is used as high frequency,wide band balun and it can make that the 75ohm coaxial-cable and the antenna get matched.(4) Design of the SQEA. In order to achieve expected pattern,the edge of the UWB planar dipoles antenna is optimized and a shield quarter-ellipse antenna(SQEA) is raised.SQEA has expected input impedance and its front-to-back ratio (F/B) can reach 35dB which can effectively avoid the unexpected noise from the poor environment.(5) Suppression of jamming pulse in synchronization system.UWB pulse coupled from the pluser and transmitted by the antenna employs itself as jamming in the synchronization system. So the circuit based on optical coupler(OC) and transient voltage suppressor (TVS) is designed to isolate and filter the jamming pulse. Testing results show the the method can effectively avoid error trigger and improve the precision of the synchronization system.(6) Design of the software.The software system is programmed under windows OS.It achieves the performance of real-time data acquisition,transfer,processing, A-scan、B-scan imaging, store and controlling system.The main innovation points of the paper are as follows:(1) Single stage series-wise avalanche circuit is designed and applied in the UWB Pulse-GPR system as the UWB pulser.Testing results show that the pulse outputed by the pulser has several advantages such as high frequency stability,high waveform stability,high repetition frequency. This is necessary that the pulser can be used in the Pulse-GPR system. The amplitude and spectrum of the pulse are suitable in the pulse-GPR system for the application of TGP.(2) The paper investigated the split of radiation pattern when Bowtie antenna works on high frequence(compared to its structure).Two methods(the RL-loading, RF transformer matcher) is raised in this paper to get the match between the pulser and the antenna.(3) SQEA is raised in this paper to achieve expected F/B and shield performance.(4) The circuit based on optical coupler(OC) and transient voltage suppressor (TVS) is designed to suppress jamming pulse.It can improve the precision of the synchronization system.更多还原