【作者】 漆汉宏；

【导师】 田永君； 郑东宁；

【作者基本信息】 燕山大学 ， 材料学， 2004， 博士

【摘要】 本论文论述了直流超导量子干涉器（dc-SQUID）的基本物理原理。根据 dc-SQUID 的等效电路理论,推导了描述 dc-SQUID 特性的方程组。通过将方程组中相关参数的归一化处理,提出了一种基于 Matlab 工具软件对对称性高温超导双晶结 dc-SQUID 特性进行仿真研究的简便方法,仿真结果与理论分析结果一致,对实际设计和研制高温超导 dc-SQUID 器件时,各参量的确定提供了有力的依据。 基于双晶晶界 Josephson 结,设计了一种磁聚焦 B 型方垫 dc-SQUID,SQUID 中心方孔尺寸为 30μm×30μm,外围方垫尺寸为 8mm×8 mm,电感约为 47pH。采用脉冲激光沉积工艺,在 STO（100）衬底基片上制备了纯 c取向、杂相很少的高质量高温超导 YBCO 薄膜。采用标准掩膜光刻和刻蚀工艺,将制备的 YBCO 薄膜成形为 dc-SQUID 器件。利用自行研制的一套基于 Labview 的计算机虚拟仪器数据采集测试系统,对 dc-SQUID 特性进行了测量。测试结果表明:所研制的垫圈型双晶结高温超导 dc-SQUID,临界电流约为 55μA,IcR 值达到 110μV。调制频率为 50kHz,磁通锁定模式下工作的磁强计,在无超导屏蔽的条件下,白噪声区磁场分辨率达到333fT/Hz1/2,磁通分辨率为 14.5μΦ₀/Hz^1/2。 对于在无屏蔽环境下普遍采用的高温超导 dc-SQUID 一阶平面式磁场梯度计进行了图形结构的优化设计。外围天线尺寸为 9mm×9 mm 的一阶平面式梯度计,梯度计基线长度（b）为 6mm,中心 SQUID 环孔尺寸为 4μm×110μm,线宽为 5μm 时,bAeff 参数达 0.7mm³。在 10×10mm2 基片上制备了这种高温超导 dc-SQUID 平面式梯度计,并对其性能进行了测量,测试结果表明:所研制的高温超导一阶平面式梯度计,白噪声区磁通分辨率为 15μΦ₀/Hz^1/2,磁场梯度分辨率达到 443 fT/cmHz^1/2。 应用所研制的磁强计建立了一套高温超导 dc-SQUID 无损检测系统。根据涡流检测的原理,对多层铝板进行了无损检测实验研究,结果表明:高温超导 dc-SQUID 能够有效的应用于无损检测中,多层铝板内部十几 mm甚至几十 mm 深度存在缺陷的情况下,可以明显地看到缺陷引起的附加信号,灵敏度很高,扫描出的图像可以显示出缺陷的位置。但是,到目前为止,由于还没有一个确定的数学模型能够定量地描述缺陷大小和附加信号大小之间的关系,因此我们还不能确定附加信号宽度和缺陷大小在数值上的对应关系。更多还原

【Abstract】 In this thesis, we describe the basic physical principle of direct current superconducting quantum device （dc-SQUID）. The equations describing the characteristics of dc-SQUID are derived according to the equivalent circuit theory of dc-SQUID. By normalizing the related parameters in these equations, a simple simulating way based on Matlab tool software for symmetrical high temperature superconducting （high-T_c） dc-SQUID with bicrystal junctions is proposed. The simulating results are very consistent with the theoretical analysis and provide reliable basis for ascertaining dc-SQUID parameters when we practically design and fabricate high-Tc dc-SQUID devices. We design a washer type of flux-focused dc-SQUID based on bicrystal grain boundary Josephson Junction. The central square hole and the outer square washer of the SQUID are 30μm×30μm and 8mm×8mm, respectively. The SQUID inductance is estimated about 47pH. High quality high-Tc YBCO thin films with pure c-axis orientation growth and few outgrowths are fabricated on STO（100） substrates by using pulsed laser deposition （PLD）. The dc-SQUID devices are patterned with the fabricated YBCO thin films by standard mask photolithography and etching methods. The measurements of the characteristics of the dc-SQUIDs are carried out with a set of computer-controlled virtual instrument data acquisition system based on Labview which is developed by ourselves. The testing results show that the critical current of the fabricated washer-type high-Tc dc-SQUID with two bicrystal junctions is about 55μA with its IcR of about 110μV. For the magnetometer operated on flux locked mode with 50kHz modulation frequency, its magnetic field sensitivity is about 333 fT/Hz^1/2 at white noise zone and the corresponding flux sensitivity is about 14.5μΦ₀/Hz^1/2 in non-superconducting shielded environment. The optimization for the configuration of first-order planar high-Tc dc-SQUID gradiometer which is widely used in unshielded environment is also involved in this thesis. For the optimized first-order planar gradiometer with the outer antenna size of 9mm×9 mm, the baseline length b is about 6mm. When the central SQUID hole is 4μm×110μm and the SQUID line width is 5 μm, the parameter bAeff for the planar gradiometer has the maximum value of 0.7mm³. The first-order planar gradiometer is fabricated on 10×10mm2 substrate and its characteristics are also tested. The testing results show that the flux sensitivity of the fabricated high-Tc dc-SQUID first-order gradiometer is about 15μΦ0/Hz1/2 at white noise zone and the corresponding magnetic field gradient resolution is 443 fT/cmHz^1/2. A nondestructive evaluation （NDE） system with the fabricated high-Tc dc-SQUID magnetometer has been built up based on eddy current NDE. The NDE experimental results for several aluminium plates show that the sensible high-Tc dc-SQUID NDE can be effectively applied in nondestructive evaluation. When flaws are over ten and even several tens millimeters below the sample surface, the additive signals from the flaws can be clearly identified. By mapping the electric field distribution, we can locate the flaw position. Up to now, however, no appropriate model can quantitatively describe the relationship between additive signals and the real size of the flaw. Therefore, we cannot determine the corresponding numeric relationship between observed additive signals and flaw shape.更多还原