共查询到20条相似文献,搜索用时 156 毫秒
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Fabbri M. Albano P.G. Pretelli M. Negrini F. Ohsaki H. 《Applied Superconductivity, IEEE Transactions on》2001,11(4):4116-4122
A pulsed magnetic field can be applied using small coils to generate a strong magnetic field for the magnetization of the high-Tc superconductors (HTS) to be used as quasi-permanent magnets in flywheels and motors. The dynamic electromagnetic behavior of two melt-processed ring-shaped Y-Ba-Cu-O bulks using the pulsed field magnetization (PFM) process has been experimentally investigated and analyzed. The flux trapped in the bulk by PFM process was compared to the flux trapped by field cooling process. Both cases then have been analyzed with a numerical model based on the finite-element method (FEM). The power-law model was utilized to relate the electric field to the current density inside the superconductor. The dependence of the critical current density on the magnetic field density was taken into account. Measured and calculated results are compared and discussed 相似文献
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Chunyong He Yang Hou Liang Liu Zhengxiang Gao 《Applied Superconductivity, IEEE Transactions on》2004,14(4):2025-2030
The distributions of the magnetic field and temperature in a superconducting-disk magnetized by pulse field, and the levitation force between this disk and a permanent magnet are calculated. The calculation is based upon the current motion and the heat diffusion equations in the disk. The critical current density as a function of magnetic field and temperature is taken into account. The dissipation power in the superconducting or the normal state region is distinguished. The trapped field may reach 17 T at 29 K by pulsed field magnetization. The effects of the amplitude of the current pulse on the distributions of magnetic field in the disk and on the levitation force are discussed. 相似文献
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针对高空核电磁脉冲(high altitude electromagnetic pulse,HEMP)试验研究,分析了电小环天线测量原理和频率特性,建立了传感器数值模型,研究了其脉冲接收特性,设计了一种B-dot传感器,研制了一套脉冲磁场测量系统.结果表明:当环面半径小于20 mm,传感器的上限截止频率达到720 MHz以上,标定结果显示测量系统整机的上升时间小于1 ns.应用该系统测试HEMP模拟器的电磁脉冲环境,并与电场测量结果进行了比对和验证,结果与理论相符,该系统具备HEMP模拟器产生的快前沿脉冲磁场的测量能力,同时可推广应用于其他强脉冲磁场测量. 相似文献
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Xiaosong Li Qiaofu Chen Jianbo Sun Yu Zhang Long G. 《Applied Superconductivity, IEEE Transactions on》2005,15(3):3808-3813
In a high-temperature superconducting (HTS) transformer, the leakage magnetic field decreases the critical current and increases the ac loss in the tapes. Moreover, because of nearly zero resistance of HTS tapes, a slight unbalance of the branch inductances of the windings might result in heavy circulating current. So, the numerical analysis of the leakage magnetic field and circulating current is especially necessary for an HTS transformer design. In this paper, the influence of the winding configurations on the stray field and circulating current is studied. That is, the magnetic field distribution is analyzed by finite-element method and then, based on the inductance matrix obtained after a magnetic field analysis, the circulating current is calculated by circuit analysis. Some measures for improving the leakage field and circulating current distribution are also proposed to make HTS transformers more efficient. 相似文献
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《Applied Superconductivity, IEEE Transactions on》2008,18(3):1698-1703
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潘征石立华熊久良李跃波黄刘宏 《微波学报》2019,35(2):1-5
低频脉冲磁场对屏蔽体的耦合效应与低频磁场自身参数、屏蔽体尺寸、材料特性及屏蔽体结构有关,作用过程比较复杂,实际耦合强度和规律应以试验研究结果确定。目前关于时变磁场的研究成果主要集中在单频磁场、快沿磁场等方面,而且效应试验研究较少。针对此种情况,文章选取钢板、纯铁板和铜板等几种常用的金属材料,制作了相应的屏蔽体缩比模型,利用低频脉冲磁场模拟试验系统研究了两者的耦合规律,分析了电磁参数等因素对耦合特性的影响,在一定程度上弥补了目前研究成果的不足。 相似文献
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理论分析了光学脉冲磁场传感器中偏振方位角对灵敏度和信噪比的影响, 提出了用偏振方位角的大小来提高脉冲磁场传感器灵敏度的方法。实验结果表明, 当偏振方位角分别为45°, 60°, 70°和80°时对应的灵敏度为1.8/T,1.9/T,2.9/T和4.6/T,因此增加偏振方位角可提高磁场传感器的灵敏度。实验结果和理论分析相吻合,验证了此方法的正确性。 相似文献
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《Antennas and Propagation, IEEE Transactions on》2009,57(8):2260-2269
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The switching time of a-Si thin-film transistors (TFTs) was measured. During pulsed operation there are dynamic changes of threshold voltage (V t) and gate capacitance which occur mostly on a time scale ranging from microseconds to milliseconds. These can be qualitatively explained in terms of the fraction of the induced channel charge which is trapped in deep states in the semiconductor, and its spatial distribution. The value of V t can decrease by a much as 3 V during a pulse and also depends on the duty cycle. In pulsed operation, V t is always less than the static value; hence, the current output will be higher than calculated from the static characteristics and will depend on the duty cycle. The effective mobility remains nearly constant with changes of operating cycle. The change in source-gate capacitance confirms the inward diffusion of the trapped charge 相似文献
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《Microwave Theory and Techniques》1983,31(8):613-624
The use of modulation schemes in short-range microwave field sensors are discussed and in particular the ideas are applied to low-cost self-detecting doppler sensors based on a two-terminal negative resistance diode oscillator which acts as a load variation detector. FM-CW and pulse modulation techniques are described which can lead to improved performance in these sensors, and experimental results of bias modulation, varactor modulation, and pulsed operation of transferred-electron oscillators are presented. Modulation techniques can be applied in order to eliminate false alarms due to unwanted targets by enabling the doppler sensor to measure or discriminate target range, and the potential merits of different schemes based on frequency modulation with linear and sinusoidal modulation patterns are explored. A novel environmental profiling technique is proposed which exploits the response of frequency-modulated sensors to multiple stationary targets for use in a versatile short-range surveillance system employing digital processing techniques. The mechanism of pulsed operation in self-detecting sensors is described, and the effects of temperature variations in the active device, which result in frequency chirp, are considered. The technique of extracting the doppler signal from the pulsed bias current using a pulse cancellation circuit is demonstrated, and the effects of bias current changes during the pulse (due to temperature variations) on the use of this type of circuit are discussed. 相似文献
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光镊已成为捕获和操纵微米尺度粒子和生物细胞的有效手段,而目前常用的光镊光源为连续激光或长脉宽的脉冲光。提出飞秒激光光镊的概念.将飞秒激光序列脉冲视为对连续光的周期抽样,借助于连续光光镊的分析方法,建立了飞秒激光光镊对电介质微粒产生的轴向光学力的理论模型。给出影响捕获微粒的主要因素,指出存在最佳束腰半径和被捕获粒子半径。数值计算结果表明选取合适的飞秒激光脉冲能量、束腰半径、脉冲波长以及微粒与周围媒质的相对折射率.微米尺寸的微粒完全能被飞秒激光稳定捕获。综合考虑被捕获微粒所受的脉冲式光学梯度力、重力和布朗惯性力的作用,讨论了飞秒激光光镊轴向光学梯度力的脉冲式特点及实现稳定捕获的条件。 相似文献
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基于有限元分析法的激光剥离技术中GaN材料瞬态温度场研究 总被引:1,自引:0,他引:1
用有限元分析法模拟计算Al2O3/GaN的激光剥离,分析了采用不同能量密度脉冲激光辐照时GaN材料内的瞬态温度场分布。采用波长248nm的KrF准分子激光器对Al2O3/GaN样品进行激光剥离实验。实验结果与有限元数值模拟结果一致。分析了影响GaN材料温度场分布的因素,在激光光源一定的条件下,温度随时间和深度变化较快。在实现激光剥离时,脉冲激光的能量密度应不低于阈值条件,但为了避免温度过高对器件产生损伤,脉冲激光的能量密度存在上限。多脉冲激光辐照时,脉冲频率是另一关键参量,计算得到了不同能量密度的脉冲激光辐照时频率的选取范围。 相似文献
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提出了磁场辅助激光沉积类金刚石(DLC)膜技术,在硅基底附近添加磁力线向基底收拢的磁场,用以迫使侧向飞行的离子向基底靠拢并参与成膜。由于离子向基底的集中,使其在膜层中含量大幅上升,间接地减少了大颗粒的比例,因此,与无磁场条件下制备的DLC膜相比,引入磁场不仅提高了DLC膜的沉积速率,而且提高了其机械硬度;更重要的是,间接地证明了激光对靶材离化的高效性,为脉冲激光沉积(PLD)结合磁过滤技术提供了可行性的依据。 相似文献
14.
Pulsed-field magnetization of a bulk high Tc superconductor (HTS) is evaluated by using a macroscopic numerical simulation code. Local heat generation in the HTS during the pulsed-field magnetization is discussed to clarify the dynamic magnetization process. Nonlinear dependence of shielding current on the dynamic magnetic field is considered by using the flux flow-creep model. Dependence of flow resistivity on the magnetic field and temperature are also evaluated with the Bardeen-Stephen and the Tinkham models. It is numerically confirmed that reported experimental results are due to a decrease of the shielding current caused by local heat generation 相似文献
15.
Sivasubramaniam K. Huang X. Laskaris E. T. Zhang T. Bray J. W. Forgarty J. M. Nold R. A. 《Applied Superconductivity, IEEE Transactions on》2006,16(4):1971-1975
High-temperature superconducting (HTS) coils are generally stable against transient thermal disturbances. Protection against spontaneous quenches is not a main design issue for an HTS coil. However, HTS coils used in many electric devices such as motors, generators, transformers, and current limiters will operate under over-current fault conditions, which may result in a coil quench and thermal runaway. Those electric devices should be able to ride through some grid fault conditions and remain functional. This requires a certain over-current capability of the HTS coils. This paper discusses the over-current requirements from grid faults and the thermal transient responses of a BSCCO coil. It presents the analysis results of the coil subjected to over-current pulses at different operating conditions. The study also investigates the thermal runaway current and its relationship with the over-current pulse 相似文献
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该文以非合作水声脉冲信号为对象,研究非合作条件下水声信号的单水听器匹配场定位。首先根据水声脉冲信号的短时瞬态非平稳特性,设计具有自适应径向高斯核函数的时频分布进行频率估计。然后利用声场传播模型计算声场,求解海洋信道脉冲响应。由计算出的信道脉冲响应和水听器上的接收信号,使用时域最小二乘的方法得到搜索网格区域上的拷贝场信号。最后通过建立误差代价函数,获得表征目标位置的模糊表面,实现利用单个水听器对非合作水声脉冲信号的匹配场定位。通过仿真实验和实际海试数据的验证,证明了该方法的有效性。 相似文献