电小甚低频发射天线的地损耗电阻计算与分析

针对电小甚低频发射天线辐射电阻小,地损耗影响天线辐射效率的问题,文中研究了基于解析法计算分区域均匀辐射状地网区内磁场损耗电阻、电场损耗电阻和地网区外磁场损耗电阻、电场损耗电阻的方法,根据该方法可实现对分区域均匀辐射状地网的损耗电阻计算.计算结果表明,电小甚低频发射天线的磁场损耗电阻是地损耗的主要部分;此外,在地网总长度和地网敷设区域半径不变的条件下,均匀辐射状地网并不是甚低频天线的地网敷设最佳模式.基于上述结果,提出通过分区域敷设均匀辐射状地网的方法来降低地损耗电阻,为进一步提高电小天线的辐射效率提供了一种新的途径,具有一定的理论和工程实践指导意义.     

SiC基IGBT高铅焊料芯片固晶层的热冲击失效机理

目前大功率SiC IGBT器件常用高熔点的高铅焊料作为固晶材料，为保证功率器件的长期使用，需研究温度冲击条件下高铅焊点的疲劳可靠性，并探究其失效机理。采用Pb92.5Sn5Ag2.5作为SiC芯片和基板的固晶材料，探究温度冲击对固晶结构中互连层疲劳失效的影响。结果表明，温度冲击会促进焊料与SiC芯片背面的Ti/Ni Ag镀层反应生成的块状Ag₃Sn从芯片/焊料层界面往焊料基体内部扩散，而焊料与Cu界面反应生成的扇贝状Cu₃Sn后形成的富Pb层阻止了Cu和Sn的扩散反应，Cu₃Sn没有继续生长。750次温度冲击后，焊料中的Ag与Sn发生反应生成Ag₃Sn网络导致焊点偏析，性质由韧变脆，焊点剪切强度从29.45 MPa降低到22.51 MPa。温度冲击模拟结果表明，芯片/焊料界面边角处集中的塑性应变能和不规则块状Ag₃Sn导致此处易开裂。     

金属/p-GaAs界面态对接触电阻作用机理的研究

本文针对大功率垂直腔面发射激光器(vertical cavity surface emitting laser, VCSEL)阵列热阻大、出光不均匀的问题,研究p-GaAs层欧姆接触电阻值的作用机理,降低欧姆接触串联电阻的方法,以提高VCSEL阵列出射光功率的均匀性。基于3种常用欧姆接触金属Ti/Au、Ni/Au、Ti/Al/Ti/Au,研究各层金属厚度和金属组合对与p型欧姆接触电阻的作用规律;结合等离子体表面处理工艺,改变金属/p-GaAs界面态,研究界面态对欧姆接触电阻的影响规律。实验对比分析得到金属Ti/Au结构电极欧姆接触的比接触电阻率最低,为3.25×10^-4 Ω·cm²;基于金半接触势垒模型,通过表面等离子体处理,界面势垒可降低12.6%(0.269 2 eV降至0.235 3 eV),等离子体轰击功率可调控金半界面的势垒和态密度。     

厚膜钌系应变电阻浆料的研究

讨论了影响应变系数的有关因素:(1)电阻的组成与应变系数K的关系;(2)电阻的烧成时间与K的关系,(3)导体与K的关系;(4)玻璃与K的关系。同时论述了应变电阻的导电机理、作用原理以及应变系数的测量与计算方法等。     

三维堆叠封装TSV互连结构热扭耦合应力分析与优化

建立了三维硅通孔(TSV)芯片垂直堆叠封装结构有限元分析模型,对模型在热扭耦合加载下进行了仿真分析;分析了TSV材料参数与结构参数对TSV互连结构热扭耦合应力的影响;采用了响应面与模拟退火算法对在热扭耦合加载下TSV互连结构参数进行优化设计。结果表明：TSV互连结构最大热扭耦合应力应变位于铜柱与微凸点接触面外侧;微凸点材料为SAC387时,TSV互连结构热扭耦合应力最大,该应力随SiO₂层厚度的增大而增大,随铜柱直径的增大而先增大后减小,随铜柱高度的增大而减小;最优参数水平组合为铜柱直径50μm、铜柱高度85μm、SiO₂层厚度3μm,优化后的最大热扭耦合应力下降了5.3%。     

p—GaP与Au／Zn／AuSb的欧姆接触

用 SEM,AES 和 XRD 研究了 Au/Zn/AuSb 多层金属结构与 p-GaP 在525℃合金化4min 后,它们所形成的金属一半导体层的基本特性。当 GaP 的 p 型层空穴浓度是5×1.0~(18)cm~(-3)时,测量出它的比接触电阻是4×10~(-4)Ω·cm~(-2)。它比 AuZn 合金所形成的比接触电阻降低了一个数量级,从而形成了良好的金属-半导体欧姆接触。     

P~+-n~+隧道结的比接触电阻

本文根据Kane的直接隧穿理论,结合欧姆接触的特点,导出了p~+-n~+隧道结比接触电阻的计算公式.此式适用于直接能隙半导体,也适用于Si.在N_D+5×10~(20)cm~(-3)的磷浓度下,对一系列N_A值,按此式计算了Al/n~+-Si的比接触电阻R_(co)结果与Finetti等的测量值在数量级上完全一致.证明AL/n~+-Si的R_c基本上由其中的p~+-n~+结决定,因而与合金工艺有密切关系.     

自旋对二维极化子能量温度和磁场特性的影响

当同时考虑温度和磁场的作用时 ,应用线性组合算符法研究了电子自旋对弱耦合二维磁极化子能量的影响。对 Ga As半导体所作的数值计算结果表明 ,不同方向的电子自旋使弱耦合二维磁极化子的能级分裂为两条。随着磁场的加强 ,能级分裂得越显著。电子自旋能量与磁极化子能量之比随磁场或温度的增加而增大     

4G用漏泄同轴电缆设计与性能研究

本文对漏缆的主要电气性能指标进行了简要阐述,分别介绍衰减、耦合损耗、系统损耗。着重研究分析了内导体尺寸、外导体包覆、外导体开槽形式对衰减、耦合损耗和系统损耗的影响,为4G用漏泄同轴电缆设计提供参考依据。     

大直径波纹内导体同轴慢波结构特性的研究

提出了易以加工的大直径波纹内导体相对论返波振荡器慢波结构,推导了这种慢波结构的冷色散方程和耦合阻抗计算公式,数值计算并详细分析了相关结构参数对TM_0n模式色散曲线分离度以及TM₀₂模式的高频场耦合阻抗的影响.结果表明:慢波结构周期、波纹深度以及电子注平均半径都对高频场耦合阻抗有影响;这种慢波结构在抑制模式竞争、以及在低引导磁场下工作等方面都有较大的优势.     

Theory and analysis of leaky coaxial cables with periodic slots

Frequency band and coupling loss are the two important parameters of leaky coaxial cables with periodic slots. The frequency band can be predicted by analyzing the arrangement of the slots on the outer shield of the cable, but the coupling loss is not so easy to determine by classical methods. In this paper, the finite-difference time-domain (FDTD) method is used to calculate the electric field distribution in the slot cut in the outer conductor of the coaxial cable. The dyadic Green's function is then used to calculate the radiation field of the equivalent surface magnetic current densities. By these two methods, the coupling losses of the leaky coaxial cables with different periods, sizes and shapes of the slots can be accurately obtained. Some results in this paper were verified by the experimental results of leaky coaxial cables designed for railway mobile communications with a frequency band of 100-500 MHz     

A Semiempirical Model to Determine HF Copper Losses in Magnetic Components With Nonlayered Coils

While in numerous power electronics applications, transformers and inductors with nonlayered windings are used, the absence up until now of any theoretical or even empirical model for their HF effective resistance calculation leads magnetic component designers to make high-error approximations. The typical approach until now has been to consider them as layered and apply some of the existent relevant models. The present paper establishes a new semiempirical model for the accurate determination of HF copper losses in windings with the random conductor distribution, a case that cannot be treated by any analytical method. This model is based on the statistical treatment of numerical results coming from a large number of simulations carried out with finite-element analysis software, and incorporates only three easily determinable parameters. The selected range for each of these parameters ensures that the model is suitable for the majority of practical applications. The theoretical analysis is verified by experimental measurements on different forms of winding geometries. A detailed investigation of the new formula reveals its inherent advantages on copper loss calculation when designing nonlayered coils.      

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.     

自旋对晶体内弱耦合磁极化子性质的影响

本文采用线性组合算符和微扰法研究极性晶体中弱耦合磁极化子的性质。在计及电子在反冲效应中发射和吸收不同波矢的声子之间的相互作用时,讨论电子的自旋对极性晶体中弱耦合磁极化子基态能量的影响。结果表明,在不同电子自旋状态下,磁极化子的基态能量Ｅ０随磁场Ｂ的增大而减小;电子自旋能量与Ｅ０之比随Ｂ的增加而增加。     

Magnet cable technology development for high-temperature superconductor composite wire

Magnet cabling technology has been developed for Bi-based HTS composite wire. Concentric round cabling as well as Rutherford cabling has been proven in > 100 m lengths. For Bi-2223 precursor composite wire, post-cabling deformation is required to achieve high transport engineering current density (J_e), and early results have reached 5500 A/cm² at 77 K and self-field. Cable-and-deform conductor has similar magnetic field retention and anisotropy as conventional, nontransposed multifilament Bi-2223 composites with comparable J_e. HTS magnet cabled composites have great potential for providing high I_c, J_e, and reducing fabrication cost.     

自旋对强耦合二维磁极化子基态能量的影响

采用线性组合算符法研究电子自旋对强耦合二维磁极化子基态能量的影响．对ＫＩ晶体所作的数值计算结果表明,随着磁场的加强,不同取向的电子自旋使强耦合二维磁极化子基态能量表现为增加和减少两种截然相反的情形．电子自旋能量与磁极化子基态能量之比随磁场的增加而增加．     

High Field Superconducting Solenoids Via High Temperature Superconductors

High-field superconducting solenoids have proven themselves to be of great value to scientific research in a number of fields, including chemistry, physics and biology. Present-day magnets take advantage of the high-field properties of Nb₃Sn, but the high-field limits of this conductor are nearly reached and so a new conductor and magnet technology is necessary for superconducting magnets beyond 25 T. Twenty years after the initial discovery of superconductivity at high temperatures in complex oxides, a number of high temperature superconductor (HTS) based conductors are available in sufficient lengths to develop high-field superconducting magnets. In this paper, present day HTS conductor and magnet technologies are discussed. HTS conductors have demonstrated the ability to carry very large critical current densities at magnetic fields of 45 T, and two insert coil demonstrations have surpassed the 25 T barrier. There are, however, many challenges to the implementation of HTS conductors in high-field magnets, including coil manufacturing, electromechanical behavior and quench protection. These issues are discussed and a view to the future is provided.     

Simple derivation of the expression for the synchronous field in circular cylindrical cavity gyrotrons

It is shown that the expression for the synchronous field at any point in a circular cylindrical cavity can be easily obtained using Graf's formula. The result is applied to the calculation of cavity-beam coupling impedances. Results for the ratio of coupling impedances in tubes using magnetron injection guns and tubes in which the guiding centre of the electron beam is on the cavity axis are given. For operation at half the cyclotron magnetic field, the coupling impedance is much higher for tubes of the second type.     

A High-Power UHF Circulator

The insertion loss, the bandwidth ratio, and the nonlinearity of a high-power UHF circulator are discussed generally with regard to the characteristics, volume, and filling factor of the ferrite. Theory and experiment are made on the high-power circulator with ferrite, where either surface of the ferrite comes into contact with air. A wideband technique in improving the narrowband that is essentially the result of the filling factor of ferrite is also described. To avoid the center conductor heating effect, a circulator without a center conductor is described. Experiments have proven that, for ferrite nonlinearity, the threshold power by spinwave occurs in a polycrystal for CW power even above resonance and is changed by a external field strength, whereas the nonlinearity is not observed in a single crystal.