含有部分填充等离子体柱的螺旋线混合模的理论分析

导出了含有部分填充等离子体柱的螺旋线中混合模的色散方程,计算出混合模的色散曲线并由此探讨了混合模的形成条件。研究了约束磁场对轴向电场的径向分布的影响。在低约束磁场下轴向电场的径向分布显示场与电子束的耦合显著增强,无聚焦磁场时存在着沿等离子体柱面传播的 TG模。     

Effect of Contact Mode on the Electrical Transport and Field‐Emission Performance of Individual Boron Nanowires

Vapor–liquid–solid processing of boron nanowires (BNWs) can be carried out either using a bottom‐up or top‐down growth mode, which results in different contact modes between the nanowire and the substrate. The contact mode may strongly affect the electrical transport and field‐emission performance of the individual boron nanowires grown on a Si substrate. The electrical transport and field‐emission characteristics of individual boron nanowires of different contact modes are investigated in situ using a scanning electron microscope. The contact barriers are very distinct for the different contact modes. Moreover, the transition from a “contact‐limited” to a “bulk‐limited” field‐emission (FE) process is demonstrated in nanoemitters for the first time, and the proposed improved metal–insulator–vacuum (MIV) model may better illustrate the nonlinear behavior of the Fowler‐Nordheim (FN) plots in these nanoscale systems. Individual BNWs with different contact modes have a discrepancy in their emission stability and vacuum breakdown characteristics though they have similar aspect ratios, which suggests that their electrical transport and field‐emission performance are closely related to their contact mode. Boron nanowires grown in the base‐up mode have better field‐emission performances and are more beneficial than those grown in the top‐down mode for various device applications.     

A preliminary study of mechanical switch using high temperature superconducting material

A persistent current switch (PCS) is a key component for superconducting magnetic energy storage (SMES) system because it is used to switch a superconducting coil from storage mode to transfer mode. In previous research on a mechanical PCS for SMES, a metallic superconductor made of Nb and NbTi is used as a switching material. However, recently the research of SMES coil of a high-temperature superconductor (HTS) is widely carried out, in which a PCS is also expected to work in liquid nitrogen temperature. In this paper, yttrium barium copper oxide (YBCO) bulk of HTS was proposed as a switch material, and the test on the fundamental characteristics of a mechanical contact between two YBCO bulks was carried out. As a result, a switching phenomenon between low and high resistance ranges is observed at a threshold current value in the V-I characteristics of the YBCO contact. This phenomenon is also observed after the break and make action is carried out in liquid nitrogen. It means a possibility of a superconducting mechanical switch using YBCO bulks. Furthermore, the tests indicate that a certain amount of current needs to flow before the switching phenomenon is obtained.     

23.2% laser processed back contact solar cell: fabrication,characterization and modeling

We describe the manufacturing process for interdigitated back contact back junction silicon solar cells based on laser processes, and present detailed results and analysis to our best cell efficiency of 23.24%. The manufacturing process features two laser doping steps, one for the boron doped emitter and one for the phosphorus doped back surface field. The saturation current densities of thermal oxide passivated laser doped regions are on par with furnace diffused silicon for high efficiency solar cells. Laser ablation locally defines the contact areas through the rear dielectric layer stack, and structures the rear aluminum metallization. The precision of the laser systems in conjunction with the optical setup yields line shaped doping traces with a width of 150 µm and a pitch below 500 µm. The measured optical and electrical properties of our solar cell agree well with 3D simulation results. The measured reflection, transmission, quantum efficiency and current voltage curves in dark and illuminated condition simultaneously agree well with simulation, based on the same data set, giving confidence in the result of a detailed free energy loss analysis. The bulk resistive and recombination losses are identified as the main loss contributors. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.     

Mechanical behavior and fatigue life estimation on fretting wear for micro-rectangular electrical connector

With the increasing demand to miniaturize electrical connectors and maintaining its high reliability, micro-rectangular electrical connectors are now widely used. Fretting is generally recognized as an essential failure mechanism for an electrical contact. Considerable work has been carried out to understand fretting of connectors and contact metals, by experiments and simulation methods based on a simplified “hemispheric-flat” model. It is difficult to simulate the contact interfaces between a twist pin and a socket for a micro-rectangular electrical connector. Hence, we develop a 3-D finite contact model. In the present investigation, before the fretting process caused by vibration, an additional insertion step was conducted, in order to obtain the initial state of the contact pair at mated contact surfaces when fretting occurs. We validate consistent behavior for the strand component of the twist pin during the insertion and fretting processes in the simulation. A slight stress release was observed during insertion when the bumped part of twist pin was completely inserted into the socket. The performance of the twist pin, including displacement, contact force, contact area and stress state, during the fretting process was periodically changing due to the vibration of the socket.     

辐射场中金属接触无源互调干扰研究

为了评估辐射场中金属接触结构引起的无源互调（passive intermodulation，PIM）对接收天线的干扰程度，提出并验证了一种可以预测被天线接收的PIM幅值的计算方法.应用PIM点源模型，并基于接触结处载波激励电流幅值和PIM信号耦合效率的仿真建立辐射场中金属接触PIM的计算方法；采用缝隙波导工装基于近场耦合测试原理对两根铜丝搭接而成的接触结构在缝隙波导近场辐射场中的三阶无源互调（third-order passive intermodulation，PIM₃）及其按位置分布规律进行测试分析.理论计算和实验测试结果比较吻合，证明本文提出的计算方法能够预估辐射场中金属接触PIM幅值.本研究工作为评估辐射场中PIM产物提供了分析方法，同时有助于深入理解辐射场中金属接触PIM的产生机理.     

化学沉积电极与BaTiO3系PTCR半导瓷的欧姆接触

研究了在BaTiO3系PTCR半导体陶瓷上化学沉积镍和铜电极的接触电阻及稳定性，并与烧渗Ag-Zn、烧渗Al电极进行了比较。根据实验结果，用量子力学从理论上讨论了欧姆接触的可能模型，提出场发射是金属－半导体陶瓷形成欧姆接触的机理之一。陶瓷表面经过处理后，元件的电性能要发生一些变化，但不会恶化陶瓷的体性能。     

High current pressure contacts to Ag pads on thin filmsuperconductors

High current, low resistance, nonmagnetic, and nondestructive pressure contacts to Ag pads on YBa₂Cu₃O_7-δ (YBCO) thin film superconductors were developed in this study. The contact resistance reported here includes the resistance of the current lead/Ag pad interface, the Ag pad/YBCO interface, and the bulk resistance of the contact material. This total contact resistance is the relevant parameter which determines power dissipation during critical-current measurements. It was found that regardless of the optimization of the Ag pad/YBCO interface through annealing, a pressure contact can yield a lower total resistance than a soldered contact. The lowest resistance obtained with pressure contacts was 3 μΩ (for a 2×4 mm ² contact). These contacts may be useful for many different high temperature superconductor (HTS) studies where high-current contacts with low heating are needed     

Efficient Fabrication of Ultralight YBa2Cu3O7−x Superconductors with Programmable Shape and Structure

Superconducting YBa₂Cu₃O_7−x (YBCO) bulks have demonstrated promising applications in quasi-permanent magnets, levitation, etc. Recently, the applications of bulk superconductors have been proposed, such as in portable, ultralight superconducting devices. These applications require bulk superconductors with lightweight, complex morphology, and good processability. However, the traditional fabrication method of YBCO bulks requires prolonged supplemental oxygenation and produces limited geometries with many randomly distributed cracks. This, combined with the inherent brittleness of the ceramic material, seriously impedes its wide application. In this study, a YBCO bulk with a multiscale hierarchical geometric configuration is constructed by a direct-ink-writing-based 3D-printing process. The 3D-printed YBCO green bodies exhibit a robust structure after directional freezing, which promotes intimate contact between the precursor particles in the deposited layers. This technology offers the advantage of a low shrinkage of 13.6 vol% after sintering at 920 °C. The 3D-printed bulks show lightweight, highly crystalline, and good electromagnetic properties compared with those produced by traditional cold-pressed sintering. Importantly, the multilevel void structure with a large specific surface area significantly reduces the oxygenation time and retains superconductivity. The proposed 3D-printing process can be adopted for the industrial production of superconducting bulk with complex geometries for novel applications.     

Experimental study of lightning-induced voltage on an overhead wireover lossy ground

Experiments on the lightning-induced voltage on an overhead wire with a simulated lightning channel and a 1/20 reduced-scale model have been carried out on a lossy ground. This method is quite useful in testing various coupling models as repeated measurement along with a simple simulated lightning channel is possible. The electrical characteristics of the ground, indispensable in the calculation of the induced voltage over lossy ground, are evaluated through the comparison of the measured and the calculated horizontal electric field waveforms. The coupling model adopted in the numerical calculation of the induced voltage, including the terminations of a finite line, is verified by the good agreement of the measured and the calculated voltage waveforms. This result also verifies the usefulness of the measurement of the horizontal electric field waveform in assessing the ground conductivity in the frequency range of interest     

基于热力收缩线特征的电接触载荷衰减状态在线评估方法

提出了一种基于红外特征的在役飞机电接触可靠性在线评估方法。在役飞机长期的振动、腐蚀、高温等环境负荷冲击导致电接触载体表面状况恶化,其程度往往难以定量评估。通过模型机理分析发现,斑点化特征引起接触电阻等可靠性指标下降。然后针对某型电接触载体施加一定的扭矩载荷谱,实时获取电接触部位的“热”信息。在低载荷、临近额定载荷状态下,随载荷状态变化而出现的斑点化特征较为明显。由此认为,将热力收缩线区域最高温度、等温线密集程度、连通区域面积及边界模糊化程度等作为表征指标,能够反映电接触表面施加机械载荷状态的实际衰减程度。因此,该方法可用作在役飞机接触电阻恶化程度的有效评估方法。     

Geometry-based finite-element modeling of the electrical contact between a cultured neuron and a microelectrode

The electrical contact between a substrate embedded microelectrode and a cultured neuron depends on the geometry of the neuron-electrode interface. Interpretation and improvement of these contacts requires proper modeling of all coupling mechanisms. In literature, it is common practice to model the neuron-electrode contact using lumped circuits in which large simplifications are made in the representation of the interface geometry. In this paper, the finite-element method is used to model the neuron-electrode interface, which permits numerical solutions for a variety of interface geometries. The simulation results offer detailed spatial and temporal information about the combined electrical behavior of extracellular volume, electrode-electrolyte interface and neuronal membrane.     

Propagation characteristics of high-Tc superconductinginterconnect for VLSI packaging predicted by a generalized two-fluidmodel

A generalized two-fluid model is used to analyze the propagation characteristics of high-Tc superconducting interconnects for very large scale integration (VLSI) packaging. The comparisons for surface impedance of YBa₂Cu₃O_7-x (YBCO) single crystals and thin films show data are in good agreement with the generalized two-fluid model. Based on the generalized two-fluid model, the temperature- and frequency-dependences of the attenuation constant are calculated, the transient responses of a pulse transmitted on a high-Tc superconducting interconnect are simulated, and a simple semi-empirical expression for rise time is given. The results based on the generalized two-fluid model predict an optimum operation temperature range for YBCO interconnect near at liquid nitrogen temperature     

激光淬火温度场及材料性能的数值模拟

从相变理论和热弹塑性理论出发,并结合激光淬火实验资料,建立了考虑相变过程、温度场和变物性系数的非线性耦合热传导方程;建立了相变组织与材料性能的数值计算模型。然后用有限元法进行了温度场、相变组织分布、材料性能的数值模拟。通过计算与试验结果的比较,计算结果令人满意。在获得激光淬火最佳工艺参数、预测材料性能方面有一定的实际应用价值和理论研究价值     

Minority carrier exclusion

The paper deals with a current-controlled non-equilibrium process, whereby the influx of minority carriers into a semiconducting material is smaller than the rate required for normal conduction in the undisturbed, homogeneous bulk. It is shown, within the framework of a “small signal theory”, how the corresponding concentration and field contours depend on the carrier lifetime, the mobility ratio and the current composition contact characteristics (via the exclusion ratio). The departures from electronic equilibrium can lead to a total resistance increase or a decrease, depending on the detailed combination of parameters.     

A joint field/circuit model of line-to-ring coupling structures andits application to the design of microstrip dual-mode filters and ringresonator circuits

A joint field/circuit model is proposed in this paper to characterize a class of line-to-ring coupling structures for design and optimization of microstrip dual-mode filters and ring resonator circuits. The generic model is derived from field theory and presented in terms of circuit elements by applying a newly developed numerical deembedding technique called “short-open calibration” in a deterministic method-of-moments scheme. It provides a new design strategy for characterizing and optimizing electrical performance of the line-to-ring coupling structures. Such three-port topologies are explicitly formulated by using an equivalent network having circuit elements calculated by the proposed joint field/circuit model. Three microstrip tightly coupling geometries and their related ring resonators are studied with the extracted J-inverter susceptance parameters. Experiments are performed to validate the joint model and also show coupling characteristics of the three types of line-to-ring circuit for the design of ring resonators and dual-mode filters. With this new technique, an optimized microstrip dual-mode filter is successfully designed and the prediction agrees well with our measurements     

VHF 频段漏泄同轴电缆埋地传感器研究

为了获得漏泄同轴电缆作为一种埋地探测传感器的电气特性,研究适用于周界入侵探测系统的漏泄同轴电缆,设计了一种外导体为八字形开槽的漏泄同轴电缆。基于漏泄同轴电缆的理论分析和相关行业标准,利用商业电磁仿真软件Ansoft HFSS,建立了用于计算漏泄同轴电缆传输衰减和耦合损耗等重要电气特性的电磁仿真模型,作为一种工作在VHF 频段的埋地传感器,利用实验数据分析其VHF 频段工作特性,建立了用于分析耦合损耗特性的埋地传感器系统模型,分析了结构尺寸参数对耦合特性的影响,进一步计算了漏泄同轴电缆的多个电气性能参数及其变化规律。仿真结果表明:在VHF 频段,槽口缝隙的长度、倾角会对埋设双缆的接收特性产生影响,槽口越长倾角越大则接收效率越高,作为传感器单元的LCX 对比实验表明仿真与实测的结果具有良好的一致性。     

Three-dimensional field representation in a ten-parametercylindrically symmetric anisotropic material

A vector-field representation of the electromagnetic field in a cylindrically symmetric anisotropic region is derived and discussed in terms of its usefulness as an analytical tool for studying basic wave processes in anisotropic materials. The field representation clearly displays the polarization coupling nature of an electromagnetic field in a cylindrically symmetric anisotropic material. The representation is also attractive from the practical standpoint, since the mathematical model of absolute (i.e. not relative to free-space) permeability and permittivity tensors is ideal for representing general anisotropically coated cylindrical structures. The vector problem is reduced to a scalar problem for the axial fields. In the solution of the set of second-order partial differential equations for the axial fields, a type of generalized vector cylinder function encountered when a contour representation of the Barnes type is employed for the two unknown scalars is discussed. The special case for which polarization decoupling occurs is described     

Performance of $hbox{YBa}_{2}hbox{Cu}_{3} hbox{O}_{x}$ Tapes With Different Structures Under AC Overcurrent Conditions

The voltage and temperature of $hbox{YBa}_{2}hbox{Cu}_{3}hbox{O}_{x}$ (YBCO) tapes with different structures were measured at alternating-current overcurrent conditions in liquid nitrogen. A safety temperature limit of the tapes with different structure was obtained based on the measured critical-current degradation data of the YBCO tapes. According to heat conduction model, the electrical and thermal performances of YBCO tapes were analyzed for tapes with different stabilizers. The comparison was presented for simulation and test data. The results are helpful for the design of superconducting electrical equipment.