Simulation of dielectric resonator for a high-T_c radio frequency superconducting quantum interference device

Nowadays,the high-critical-temperature radio frequency superconducting quantum interference device (high-T c rf SQUID) is usually coupled to a dielectric resonator that is a standard 10 × 10 × 1 mm 3 SrTiO 3 (STO) substrate with a YBa 2 Cu 3 O 7-δ (YBCO) thin-film flux focuser deposited on it.Recently,we have simulated a dielectric resonator for the high-T c rf SQUID by using the ANSOFT High Frequency Structure Simulator (ANSOFT HFSS).We simulate the resonant frequency and the quality factor of our dielectric resonator when it is unloaded or matches a 50-impedance.The simulation results are quite close to the practical measurements.Our study shows that ANSOFT HFSS is quite suitable for simulating the dielectric resonator used for the high-T c rf SQUID.Therefore,we think the ANSOFT HFSS can be very helpful for investigating the characteristics of dielectric resonators for high-T c rf SQUIDs.     

Basic properties of an rf SQUID involving two Josephson junctions connected in series

We have studied the basic characteristics of a radio frequency superconducting quantum interference device (rf SQUID) involving two Josephson junctions connected in series, the case for the widely used grain boundary junction (GBJ) rf SQUID. It is found that the SQUID properties are determined mainly by the weaker junction when the critical current of the weaker junction is much lower than that of the other junction. Otherwise, the effect of the other junction is not negligible. We also find that only when the hysteresis parameter β is less than 1-α, where α is the critical current ratio of the two junctions, will the SQUID operate in the nonhysteretic mode.     

Ground state of a superconducting π ring array under external magnetic fields

The ground state of a two-dimensional square superconducting π ring array has been investigated. The circulating currents of the π ring array will spontaneously magnetize to the `antiferromagnetic' arrangement with directions of the nearest-neighbouring currents circulating oppositely in the absence of an external magnetic field. It is found that the external magnetic field could destroy the anti-parallel configuration effectively. The external magnetic field needed to destroy the anti-parallel configuration is related to the superconducting \pi ring's inductance parameter β=2\pi L I_c/\phi₀. For a small β the anti-parallel configuration, which is the lowest-energy ground state of the system, will be fully destroyed and changed to the configuration that the circulating currents have the same direction and parallel to the external magnetic field when the magnetic flux reaches \phi₀/4 in each ring. Moreover, the magnetic field needed to destroy the anti-parallel configuration will be very small when β is large enough.     

颗粒超导体临界电流密度的尺寸效应

假设颗粒超导体内某点临界电流密度是该处磁场强度平均值的某种函数,计算了其实测临界电流密度与样品尺寸的关系.发现对目前实验中所用的烧结样品,实验测得的 YBaCuo超导体的临界电流密度有显著的尺寸效应.     

基于嵌入式系统的射频超导量子干涉仪控制系统

本文介绍了嵌入式系统在射频超导量子干涉仪控制系统中的应用,提出了嵌入式系统的整体方案,并对系统工作原理以及设计思想做了简要介绍.     

双结π环自发磁化的研究

研究了超导双结π环的自发磁化现象.讨论了双结π环可能发生自发磁化的条件，指出了自发磁化条件不仅与电感参数β有关，而且与两结临界电流之比有关.并通过分析自由能证明自发磁化是稳定的状态.最后给出了讨论结果和渐进行为. 关键词： 双结π环 自发磁化 自由能     

虚拟仪器在射频超导量子干涉仪控制电路中的应用

本文简要介绍LabVIEW开发的射频超导量子干涉器（rf SQUID）自动控制系统的虚拟仪器，系统可对超导量子干涉器的工作点进行调整和显示，实现了LabVIEW软件系统与第三方硬件的结合．本文将对系统工作原理、硬件电路组成和软件的设计做简要介绍．     

在SQUID心磁测量中基于奇异值分解和自适应滤波的噪声消除法

采用矩阵奇异值分解(singular value decomposition, SVD)的方法，对高温射频超导量子干涉仪(HTc rf-SQUID)采集到的单通道心磁信号进行处理.证明了对于近似周期性的心磁信号，在无参考噪声的情况下矩阵奇异值分解的方法与自适应窄带陷波相结合有较好的消除广谱噪声的效果. 关键词： 高温射频超导量子干涉仪 心磁信号 奇异值分解 噪声消除     

多结超导环在外磁场中的行为

分析和计算了双结超导环在无偏置电流时的磁通、环流、自由能与外磁场的关系.发现双结环与单结环在磁场中的行为有所不同.当两个结的Ic相等时，双结环在1＜β=2πLIcΦ0＜2时，若无偏置电流，总磁通Φ、环流I与外磁通Φe的关系仍然是非回滞的曲线.仅当β≥2时，曲线才出现回滞.另外双结环有两支解，并且每支解的周期为2Φ0. 关键词： 双结环 双支解 2Φ0周期 回滞     

在Josephson隧道结中磁场对微波感应台阶高度影响的讨论

对吴杭生等人的计算公式做了适当的简化.可减小数值计算的工作量.不通过数值计算,直接估计了磁场能使偶数标号台阶高度增大的上限标号n、对2e/h测量中用加磁场来增大台阶高度是否有意义的问题做了讨论.