平面式一阶梯度计的设计和制备及其在无损检测上的应用

我们在10×10mm2的SrTiO3双晶基片上,设计并制备了YBCO双晶结dc-SQUID一阶平面式梯度计.其基线长度为5.5mm,该梯度计能够在无屏蔽环境下稳定的工作.在77K下,200Hz时,其磁通噪声为1×10-4Φ0/Hz,能够分辨的最小磁场梯度为94pT/m.我们将该器件作为磁传感器,可以利用涡流检测的原理对非磁金属进行无损检测.实验结果表明,可以很清楚地分辨出10mm以下的缺陷.同时,我们还研究了激励线圈的尺寸与空间分辨率的关系,结果表明若激励线圈足够大,则对于梯度计和缺陷而言感受到的是均匀磁场的激励,因此涡流的分布只与缺陷的形状有关,而空间分辨率取决于梯度计的基线长度和磁场分布.     

High-Tc planar SQUID gradiometer for eddy current non-destructive evaluation

This paper reports the fabrication and test of a high-Tc SQUID planar gradiometer which is patterned from YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77K shows that the white noise at 200 Hz is about 1×10^-4 φ0/√Hz. The minimal magnetic gradient is measured and the results suggest that the minimal magnetic gradient is 94 pT/m. The planar gradiometer is used in non-destructive evaluation （NDE） experiments to detect the artifacts in conducting aluminium plates by performing eddy current testing in an unshielded environment. The effect of the exciting coil dimension on the NDE results is investigated. By mapping out the induced field distribution, flaws about 10mm below the plate surface can be clearly identified.     

基于银纳米链的马赫-曾德干涉仪结构的生物传感器

优化了一种基于表面等离激元银纳米链的马赫-曾德干涉式传感结构.该结构由参考臂、传感臂及纳米线波导构成.纳米线波导由银纳米线包裹一定厚度的硅来构成.引入两条银纳米链分别作为马赫-曾德干涉仪的参考臂和传感臂,并研究所设计结构的传输特性,通过降低传输损耗以提高所设计结构的精确度与灵敏度.相比于两条完全相同的银纳米线作为参考臂和传感臂的情况,在参考臂和传感臂改为银纳米链后,传输特性有明显提高,单位长度损耗明显降低.这是由于银纳米链中的单元结构之间的长程/库仑相互作用增强了结构中的电磁场,进而降低了传输损耗.将两条银纳米链的晶格常数设置为不同的情况,研究发现,在特定的银包硅纳米线的宽度与某些占空比下,含有非对称的银纳米链结构的单位传输损耗小于含有对称的银纳米链结构.由此可以知道,具有小损耗的银纳米颗粒链可以弥补大损耗的银纳米颗粒链的传输损失.利用这个特点,进一步优化设计结构,将一侧银纳米链改为纳米线.改变另一侧银纳米链的晶格常数与占空比,可以发现大多数情况下,这类结构传输特性优于含有两条银纳米链以及含有两条银纳米线的结构.本文的设计结构可以大幅减小传统的马赫-曾德干涉仪的传输损耗,且在结构的制备...     

高阶高温超导量子干涉器件平面式梯度计的设计

设计了一种高温超导平面式梯度计的探测线圈，利用这种探测线圈与超导量子干涉器件(SQ UID)耦合，可以制成二阶或更高阶的高温超导SQUID平面式磁场梯度计.设计的探测线 圈由两个闭合环路组成，每个闭合环路是由若干个环路通过细小的连接通道连接而成.两个 闭合环路由一条超导窄带分割，将SQUID与这条超导窄带耦合可以测出超导窄带上的电流大 小.通过调整各个环路的形状、面积和位置，可以使超导窄带上的电流与磁场的高阶梯度成 正比，从而测得磁场的高阶梯度. 通过计算，得到了各个环路的面积、电感以及位置的关 系，在理 关键词： 高阶平面式磁场梯度计 高温超导薄膜     

Study on signal intensity of low field nuclear magnetic resonance via an indirect coupling measurement

We carry out an ultra-low-field nuclear magnetic resonance (NMR) experiment based on high-T c superconducting quantum interference devices (SQUIDs). The measurement field is in a micro-tesla range (～10 μT-100 μT) and the experiment is conducted in a home-made magnetically-shielded-room (MSR). The measurements are performed by the indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using the SQUID with that achieved using a conventional low-noise-amplifier, we perform the measurements using a commercial room temperature amplifier. The results show that in a wide frequency range (～1 kHz-10 kHz) the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity as the measurement field increases. This is verified by compensating the field gradient using three sets of gradient coils.     

Millimeter Propagation and High Confinement in Rhombus-Based Hybrid Plasmonic Waveguides

A hybrid plasmonic waveguide, consisting of two dielectric nanowires symmetrically put at the opposite corner angles of a rhombic metM, is proposed and numerically analyzed by the finite-element method. Simulations show that the present waveguide can achieve the millimeter propagation distance （1244 μm） and deep subwavelength mode area （5.5 × 10-3 μm2）, simultaneously. Compared with the previous hybrid waveguides based on cylinder nanowires or fiat films, the rhombie corner angles enable our waveguide to achieve both longer propagation distance and smaller mode area. This is due to the enhanced coupling between the dielectric guided mode in nanowires and the surface plasmon polariton mode at rhombic surface. Furthermore, the extreme confinement near the rhombic corner angles can strengthen the light-matter interaction greatly and make the present waveguide useful in many applications, such as nonlinear photonics, high-quality nanolazers and nanophotonic waveguides.     

薄膜厚度对La0.67Ca0.33MnO3/Nb-SrTiO3异质结整流特性及磁阻的影响

利用脉冲激光沉积的方法,在Nb-1wt%:SrTiO3基片上分别生长了5 nm和50 nm的La0.67Ca0.33MnO3薄膜得到异质结.对该异质结电流-电压特性和磁阻的研究表明,50 nm厚的样品表现出良好的整流特性并且在外加1 T磁场的情况下无明显变化,而5nm厚的样品在低温下,整流特性发生变化,并且外加1 T磁场对其整流特性有明显影响,显示负的磁阻.通过考虑p～n结耗尽层的厚度,对观察到的实验现象进行了解释.