【作者】 汪歆；

【导师】 陈建平；

【作者基本信息】 上海交通大学 ， 电磁场与微波技术， 2009， 博士

【摘要】 微弱磁场传感器具有广泛应用,包括导航、军事、航空、航天等领域。随着窄线宽激光光源、单模光纤及相关光器件性能的不断完善,不仅光纤传感器的种类在增加,其性能也在不断地提高。光纤微弱磁场传感器因其灵敏度高,被认为是替代传统纯电学检测手段的最有竞争力的技术。基于光纤干涉仪和磁致伸缩材料的干涉型光纤微弱磁场传感器是最有望走向实用的技术之一。因此,开展干涉型光纤微弱磁场传感器的研究具有重要意义。本论文主要研究高灵敏度和稳定性的迈克耳逊(Michelson)干涉型光纤微弱磁场传感器的若干关键问题,包括:干涉型光纤微弱磁场传感器理论与原理,干涉型光纤微弱磁场换能器的设计和实现,干涉型光纤微弱磁场传感器的解调技术、磁场探测能力、稳定性与温度特性等。首先,论文系统分析和总结了干涉型光纤传感器的基本理论和Michelson干涉型光纤微弱磁场传感器的工作原理,主要包括:磁致伸缩效应与光纤中光相位的调制原理、基于Michelson光纤干涉仪的干涉型光纤传感器的结构和原理、Michelson干涉型光纤磁场传感器相位检测原理与关键技术的实现、系统不稳定的原因及其解决措施等。其次,论文对偏振无关Michelson干涉型光纤微弱磁场换能器进行了深入系统的研究,在分析干涉型光纤微弱磁场传感器系统灵敏度基础上,提出了相应的设计和制作方案。在骨架设计与制作方面,分析和对比了不同材料、形状和结构磁场换能器的性能,确定了圆柱形作为换能器的基本结构,并使用胶木材料完成了换能器骨架的制作。在Michelson光纤干涉仪设计与制作方面,建立了偏振无关Michelson光纤干涉仪可见度的数学模型,对可见度的限制因素进行详细的数值分析。计算结果表明,干涉仪臂长差是其中最重要的一项因素。借助光学精密反射仪实现了对光纤干涉仪臂长差的精确测量和控制,能有效消除臂长差对可见度的影响,臂长差可以被控制在1 mm以内,在此基础上制作出了高可见度偏振无关Michelson光纤干涉仪。在换能器设计和制作方面,在对应力和负载效应问题进行深入分析的基础上,通过反复的实验比较,确定了粘贴剂的选取原则,给出了合理、有效的粘贴方式,形成了一套磁场换能器的制作方法和工艺,并完成了换能器的制作。接着,论文研究了两种传感信号检测技术:基于硬件电路的解调技术和软件解调技术。在硬件解调方面,主要是对传统锁定放大器电路进行改进,使之具有更好的检测性能。在软件解调方面,详细研究了偏振无关Michelson干涉型光纤磁场传感器的噪声来源,包括:环境噪声、光源噪声、热噪声、散弹噪声以及电噪声等,分析了这些噪声的特点及对光纤干涉仪输出信号光相位的影响,发现热噪声是限制光纤干涉仪最小可探测相位的最主要噪声。在此基础上,提出了一种基于软件解调和自适应谱线增强器的信号解调方案,给出了具体的实现方法。论文系统测试和分析了所研制的传感器在使用硬件解调方案时的系统性能,包括:换能器机械谐振频率与频率响应,传感器系统稳定性,输入光功率和交流激励磁场幅度与系统输出的关系,传感器系统灵敏度和分辨率,以及磁场换能器方向性等。实验结果表明,在没有任何磁屏蔽措施的普通实验环境下,该磁场传感器系统具有良好的稳定性和优异的微弱磁场探测能力,最低可探测磁场在1 Hz和5 Hz处约为0.10 nT/Hz1/2和0.04 nT/Hz1/2,与目前国内已报道的同类型磁场传感器相比,具有一定优越性。本文的检测技术工作是与课题组其他同学共同完成的。然后,针对干涉型光纤磁场传感器的实用化问题,论文对干涉型光纤微弱磁场传感器的温度特性进行了分析。以弹性波理论为切入点,推导了带状磁场换能器机械谐振频率的理论模型,给出了导致机械谐振频率随外界环境温度的变化而变化的各个因素,并通过模态分析找出了其中最主要的因素。通过一系列的实验,对换能器机械谐振频率、系统输出以及系统灵敏度的温度特性进行了测试,并拟合出了相应的温度特性函数,结果显示磁场换能器机械谐振频率以及传感器系统性能会受到外界环境温度的强烈影响。在实际应用中,为了减少环境温度对系统性能的影响,论文提出两种温度补偿的方案并进行了验证。最后,对论文工作进行了总结和展望。更多还原

【Abstract】 The weak magnetic field sensors can be widely used in military affairs, aeronautics, spaceflight, and etc. With the progress and improvement of narrow linewidth laser sources, single-mode fiber and related fiber-optic devices, not only more types of fiber optic sensors have been developed but also the performances have been improved tremendously. Fiber-optic sensor detecting weak magnetic field is considered to be the most competitive alternative for traditional pure electrical detections because of its high sensitivity in theory. Fiber-optic interferometric sensors based on fiber-optic interferometer and magnetostrictive material is believed to be one of the sensing technologies that can be put into practical applications. Therefore, it is significant to carry out a study on fiber-optic interferometric sensors detecting weak magnetic field.This dissertation presents some key issues in high sensitive and stable fiber-optic Michelson interferometric weak magnetic field sensors, including theory and principle of fiber-optic interferometric weak magnetic field sensor, design and implementation of fiber-optic interferometric transducer, the demodulation schemes, the ability in detecting magnetic field, the stability and the temperature dependence of the fiber-optic interferometric sensor developed, etc.Firstly, the dissertation systematically analyzes and summarizes the fundamentals of fiber-optic interferometric sensors and the operating principles of fiber-optic Michelson interferometric sensors, including the magnetostriction effect and the principle of optical phase modulation in optical fibers, the basic structure and principle of fiber-optic interferometric sensors based on fiber-optic Michelson interferometer, the principle and realization of key techniques of phase detection of fiber-optic Michelson interferometric sensors, the cause of system instability and corresponding solving method, etc.Secondly, the dissertation investigates the fiber-optic interferometric weak magnetic field transducer based on fiber-optic polarization- insensitive Michelson interferometer. Based on the analysis of the dependent factors of the system sensitivity, the designing and implementing schemes of the key components are presented. By comparison the performances of the most popular shapes and structures that are generally adopted in fiber-optic interferometric magnetic field transducers, a cylindrical bakelite transducer framework is chosen and implemented. The performance of fiber-optic Michelson interferometer is an important factor to determine the system sensitivity, therefore the mathematical model of visibility is established for the polarization- insensitive fiber-optic Michelson interferometers so that the limitation factors of visibility can be analyzed. Numerical analysis indicates that the fiber length difference between the interferometric arms is the primary factor that limits the visibility. With the help of the precision reflectometer, the fiber length difference between the interferometric arms can then be precisely measured and maintained to be less than 1 mm to ensure high visibility. Based on the analysis of stress and loading effects, appropriate adhesive and selected and bonding methods are studied. A set of comprehensive techniques on design and implementation of the magnetic field transducer are developed through lots of experimental comparison and experience accumulation.Thirdly, the dissertation studies two kinds of sensing signal detection techniques, the hardware circuit based demodulation technique and software demodulation technique. In hardware circuit based demodulation technique, the traditional lock-in amplification circuit is modified so that a better detection can be ensured. In software demodulation technique, the noise sources of polarization-insensitive fiber-optic Michelson interferometric sensor are studied, including environmental noise, optical source noise, thermal noise, shot noise and electronic noise, etc. Their characteristics as well as their influences on the optical phase of the output signal of fiber-optic interferometers are carefully analyzed. Thermal noise is found to be the major noise to decide the minimum detectable optical phase of fiber-optic interferometer. Accordingly, a sensing signal demodulation scheme based on software demodulation and adaptive line enhancer is presented and realized. By using hardware circuit based demodulation scheme, the dissertation systematically tests and analyzes the system performance of polarization-insensitive fiber-optic Michelson interferometric sensor developed, including the transducer’s mechanical resonant frequency and frequency response, system stability, the effect of input optical power and amplitude of AC dither magnetic field on system output, system sensitivity and resolution, and the directivity of magnetic field transducer, and etc. The results show that the fiber-optic Michelson interferometric magnetic field sensor has not only good stability but also excellent ability in detecting weak magnetic field. The minimum detectable magnetic field is about 0.10 nT/Hz1/2 and 0.04 nT/Hz1/2 at 1 Hz and 5 Hz, respectively, without any mumetal shield in the ordinary laboratory environment. This part of the dissertation is collaborated with the members of the research group that the author is engaged.Forthly, the dissertation experimentally investigates the temperature dependence of the performance in fiber-optic interferometric magnetic field sensors. The cause of temperature dependence is briefly described. The theoretic model of the mechanical resonant frequency is evolved from elastic wave theory for ribbon-like magnetic field transducers based on magnetostrictive material and optical fiber. The factors that are responsible for the ambient temperature induced change of the mechanical resonant frequency are discussed. Among these factors, the primary one is analyzed by using modal analysis. The temperature dependences of the transducer’s mechanical resonant frequency, the sensor system output, and the sensor system sensitivity are tested, and the corresponding temperature dependence functions are fitted through performing a series of experiments. The experimental results show that the magnetic field transducer’s mechanical resonant frequency and the sensor system performance are strongly affected by the ambient temperature. These results also indicate that essential measures must be applied to make the measurement of the fiber-optic interferometric weak magnetic field sensor be independent of ambient temperature. Accordingly two temperature compensation schemes are presented and experiments are conducted to verify the feasibility.Last, a conclusion and expectation are made for the dissertation.更多还原