摘要
REBCO(RE为稀土元素Y、Gd等)高温超导体因其独特的抗磁特性和良好的自稳定磁悬浮性在磁浮轴承和磁悬浮轨道交通等领域具有广泛应用,超导体和永磁体之间的相互作用力特性是超导磁悬浮系统设计、制作和应用的基础,是人们研究和关注的重点。本文利用超导体与永磁体之间较大的磁悬浮力、良好的磁悬浮稳定性、以及永磁体之间较强的磁力和良好的刚性,研究REBCO高温超导块材与永磁体的组合形式对其磁悬浮力的影响,并进行了相关的应用探索,利用超导理论和磁学理论对实验结果进行了阐释。
首先,介绍了三维空间磁场和磁力测试系统的结构、工作原理和测试功能；分析了现有测试系统微弱信号采集存在的问题,并通过硬件上采用二次稳压和滤波技术,软件上采用极值和均值相结合的混合滤波算法进行了改进。实验结果表明,改进后的测试系统有效的抑制了干扰信号的影响,提高了信噪比,微弱信号的数据质量得到了明显改善；对三维磁力测量卡具进行了改进；研究了单畴GdBCO高温超导块材在轴对称、零场冷条件下的磁悬浮力特性,结合Bean模型对超导磁悬浮力的磁滞特性进行了分析。结果表明,磁悬浮力具有明显的磁滞现象,通过优化外加磁场分布和提高磁场强度,可获得较大的超导磁悬浮力；研究了场冷条件下单畴GdBCO超导块材磁悬浮力的特点,结果发现,在一定的场冷高度范围内,随着场冷高度增加,超导体的捕获磁场强度减小,磁悬浮力增大,吸引力减小。
其次,研究了永磁体的组合形式对超导磁悬浮力的影响。通过对方形永磁体的不同组态形式对单畴GdBCO超导块材磁悬浮力的影响,发现不同的磁体数量和组态形式,在超导体中产生感应环流及其半径不同,在磁体数量相同的情况下,磁极数越少感应环流半径越大；研究了条状永磁体组合形式及间距对超导磁悬浮力的影响,实验结果表明,采用最佳的三个条状永磁体比两个条状永磁体组成的组合磁体可使超导体获得较大的磁悬浮力,并结合磁体的磁场分布进行了分析和解释；研究了超导体相对于永磁体做横向运动时对其磁悬浮力的影响,在此基础上,提出了获得较大的悬浮力的可能途径；研究了条状永磁体的组合形式对超导磁悬浮导向力的影响规律、以及辅助永磁体对单畴GdBCO超导块材磁悬浮力的影响规律,并利用电磁场有限元法(FEMM)分析解释了其磁场变化规律。结果表明,当超导体与永磁体的组合形式为HTS-(PM-PM↑-PM)时,系统的超导磁悬浮力最大；当超导体与永磁体的组合形式为HTS-(PM↓-PM↑-PM↓)时,系统的磁悬浮导向力、以及磁悬浮系统的稳定性更好。当测量轴对称情况下超导体与圆柱形永磁体(磁体的N指向超导体)的磁悬浮力时,在超导体两侧引入两个辅助永磁体,当放在超导体两侧的辅助永磁体磁极N指向GdBCO超导块材PM↓-(PM-HTS-PM)时,系统的磁悬浮力及其刚度得到明显提高；当辅助永磁体的磁极N竖直向上PM↓-(PM↑-HTS-PM↑)时,磁悬浮力则减小。比较系统地研究了聚磁极的引入及其宽度变化对超导磁悬浮力的影响,发现引入宽度合适的聚磁材料可提高磁体的磁场强度和超导体的磁悬浮力。
研究了轴对称情况下辅助永磁体的磁极取向对单畴GdBCO超导块材的捕获磁场分布和磁悬浮力的影响,实验结果表明,当辅助永磁体相对于测量用永磁体的磁极取向相同时,磁悬浮力减小；磁极取向相反时,磁悬浮力增加。研究了非轴对称情况下,超导体的捕获磁场对其磁悬浮力的影响,发现超导体和测量用永磁体间的磁悬浮力与磁化用永磁体相对于GdBCO超导块材的水平位置(x)密切相关,当x=0、测量用永磁体的磁极与被磁化GdBCO超导块材的磁极取向相同(PMl1↓-SCPM↓)时,超导体的磁悬浮力最小；当x=0、测量用永磁体的磁极与被磁化GdBCO超导块材的磁极取向相反(PM1↓-SCPM↑)时,超导体的磁悬浮力的最大。
最后,在超导磁悬浮系统(HTS-PM)中引入永磁磁悬浮(PM-PM)。研究了场冷高度对超导磁悬浮和混合磁悬浮系统磁悬浮力的影响,并进行了对比分析。结果表明,永磁磁悬浮(PM-PM)的引入有效地提高了混合系统的磁悬浮力；就混合磁悬浮系统(HTS-PM和PM-PM)的构建形式对磁悬浮力的影响进行了初步研究,发现混合磁悬浮系统的磁悬浮力与磁体的磁场分布、以及永磁磁悬浮的合理引入等密切相关。
在以上研究的基础上,设计制作了一种磁悬浮列车演示模型,对模型设计原理和操作方法做了较为详细的叙述,分析了磁体组合形式对磁悬浮列车模型出现失稳、倾斜、跳跃、震荡、减速或停止等现象原因。
High levitation force and good self stability of REBCO (RE=Y、Gd) bulk superconductors make it possible for applications such as superconducting magnetic bearings and levitation transportation systems etc.. These applications are based on the levitation force characteristics between the superconductors and magnets, so it is very important for us to investigate the levitation properties between superconductors and magnets. In this paper, the effect of magnet configurations on the levitation force of REBCO bulk superconductor have been investigated and interpreted based on the theory of superconductivity, and a small maglev model has been designed and constructed; the main results are as following:
A levitation force and magnetic field distribution measurement system was used in this work. In order to improve the accuracy of the measurement system, a filtering circuits and a hybrid filtering algorithm have been designed and applied; the results show that the quality of signal to noise ratio has been effectively improved after the modification. A levitation force measurement device in three dimensions improved. The levitation force, between a single domain GdBCO bulk superconductor and a cylindrical permanent magnet, has been investigated in coaxial symmetry at zero field cooling state. The results show that the levitation force has an obvious hysteresis and directly dependent on the applied magnetic field, and higher levitation force can be obtained by optimizing the magnetic field during the measurement process. It is also found that the repulsion force increases and the attractive force decreases when the field-cooling height between the single domain GdBCO bulk superconductor and permanent magnet increases. The results are well interpreted based on the Bean model.
The effect of magnet configurations on the levitation force of a single domain GdBCO bulk superconductor has been investigated. For small cubic permanent magnets(less than the size of the GdBCO bulk), it is discovered that the levitation force is closely related with the number and configuration of cubic permanent magnets, for a given number of cubic magnets, the fewer the cubic magnet number and the magnetic poles, the higher the levitation force of the superconductor; For small bar magnets(the width and height less than the length, but the length near to the size of the GdBCO bulk), It is found that reasonable configuration of assembled bar magnets(ABM) can produce higher levitation force, three bar magnets can generate higher levitation force than that of two bar magnets. The levitation force and guidance force between a bulk superconductor and assembled bar magnets has also been investigated and interpreted. It is found that the higher levitation force is obtained in the HTS-((?)-PM↑-(?)) configuration, and larger guidance force is obtained in HTS-(PM↓-PM↑-PM↓) configuration. Effects of additional permanent magnet configuration on the levitation force of a single domain GdBCO bulk superconductor have been investigated with a cylindrical permanent magnet in their coaxial configuration at liquid nitrogen temperature, the magnetic pole N of the cylindrical permanent magnet is directed to the GdBCO bulk superconductor in their coaxial configuration. It is found that the larger levitation force is obtained in the PM↓-((?)-HTS-(?)) configuration, and smaller levitation force is obtained in the PM↓-(PM↑-HTS-PM↑) configuration. The width effects of the iron for condensing magnetic field on the levitation force indicate that reasonable iron width is helpful to enhance the magnetic flux density and improve the levitation force of the superconductors.
The effect of magnetization methods with additional permanent magnet on the magnetic field distribution and levitation force of single domain GdBCO bulk superconductor have been investigated with a cubic permanent magnet in their coaxial configuration at liquid nitrogen temperature. It is found that:if the N pole of the cubic permanent magnet, during the levitation force measurement, is placed above the GdBCO bulk superconductor and in downward direction, the maximum levitation force can be improved, when the N pole of the additional cubic permanent magnet points to upward and stick together to the bottom of the GdBCO bulk. The maximum levitation force can be improved (or reduced), when the GdBCO bulk superconductor is closely placed below and magnetized by the additional cubic permanent magnet with N pole in upward(or downward) direction, and removed away after the magnetization.
The effect of lateral magnetization position(x) between a cubic permanent magnet and GdBCO bulk superconductor at fixed height on the levitation force has been measured, it is found that the largest (or smallest) maximum levitation force is obtained at x=0when the magnetic poles N of the magnetized GdBCO bulk is in a direction opposite (or parallel) to the magnetic pole N of the permanent magnet used for measurement.
A hybrid levitation system of permanent magnet-permanent magnet levitation (PM-PM) and high temperature superconductor-permanent magnet levitation (HTS-PM) has been also investigated; it is found that the levitation force and stiffness of the hybrid system can be modified by the combination of HTS-PM and PM-PM levitation.
A small HTS maglev model has been designed and constructed for the demonstration of interaction properties between the high temperature bulk superconductor and different magnet configurations, which can demonstrate the normal, instability, tilting, jumping, shocking, or stopping phenomena of the maglev gestures.
引文
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