Radiation of Nonsinusoidal Waves by a Large-Current Radiator

The calculation of the electric and magnetic field strength produced by a radiator is usually done only for distances large compared with the geometric dimensions of the radiator. This approach makes it Impossible to obtain exact relations between the power fed to the radiator by the driver, the voltage between the radiator terminals, the power radiated to or received from the near zone, and the power radiated to the far zone. This paper develops a solution for the large-current radiator that can be evaluated numerically by computer for any distance, and thus permits the calculation of the power flowing at any time through the surface of the radiator. The knowledge of this power is the basis for the design of efficient radiators.     

Power Flowing through the Surface of a Large-Current Radiator

A previously developed theory permitted us to calculate the electric and magnetic field strength produced by a current with arbitrary time variation flowing in a large-current radiator for any distance from the surface of the radiator to infinity. This permits one to determine Poynting's vector on the surface of the radiator and, by integrating it over the surface, to calculate the power flowing through the surface of the radiator at any time. One obtains the power radiated to the far zone, the power contained in the various near-zone components, and the required driving voltage. The influence of the antenna dimensions on these quantities may be studied to help with the design of better antennas.     

Lines of Force for a Hertzian Electric Dipole

The generation of electromagnetic waves by a Hertzian electric dipole having a current with a nonsinusoidal time variation is described in terms of magnetic flux lines called lines of force. The magnetic flux depends on the time variation of the current, the normalized distance from the radiator and the time variation of the integral of the current. The radiation of electromagnetic waves and their propagation is described by the lines of force in the near zone and the far zone, respectively. When the large-distance approximation is made, the magnetic flux depends on the time variation of the current only, and the lines of force generated will propagate away from the radiator. Plots of lines of force at several observation times are presented where the near zone and the far zone identified.     

磁性石榴石薄膜的磁力显微镜研究

本文采用磁力显微镜（ＭＦＭ）对磁性石榴石（ＹＧｄＢｉ）３（ＧａＦｅ）５Ｏ１２薄膜的磁畴结构进行了观察研究。实验结果表明，磁性针尖的磁特性进行对石榴石ＭＦＭ图像的影响较大，而且随着针尖与样品间距的增大，磁针尖对石榴石畴结构的影响有所降低。另外，改变针尖的磁化方向，得到的石榴石磁畴结构也有所不同。     

一种高效功放散热器的设计

针对某型功率固态功放分机功耗大、热流密度高和工作温度高的特点,对其热传递路径以及影响因素进行了分析,提出了一种内嵌VC均温板且热管贯穿肋片的高效散热器设计方案,并进行了仿真计算,论述了高效散热器制作的工艺流程并加工了产品样件。测试结果表明,与原方案相比,在单个功率管热功耗70 W,整机热功耗2 240 W的条件下,功率管温度最高下降了15.5℃,满足了使用要求,提高了产品的可靠性。     

折环劲度系数与磁场力因子的匹配

失真是扬声器的一个重要性能指标,引起扬声器失真的主要因素是折环与磁路系统的非线性。将折环和磁路系统当作一个整体来研究。介绍了折环的劲度系数如何与磁场力因子配合,以达到降低失真的效果。     

高压传输线附近磁场环境的理论分析

应用复镜象理论计算了高压传输线和电气化铁路附近磁感应强度的量值，指出了低于千分之二高斯的安全区域，并对高压传输线和电气化铁路的磁污染进行了讨论。     

一种车用电控单元散热器设计与测试

在汽车电控设备设计中,电子器件是设备中的关键器件,电子器件散热设计的好坏直接影响整个系统的可靠性.文章介绍了一种车用电控设备中50W散热器的设计,并从使用角度介绍了散热器的热导分析及散热器设计,对实验数据与仿真分析结果进行了对比分析,验证了设计的有效性.     

Magnetic Force Microscopy Images of a Nanometer‐Sized,Purely Organic High‐Spin Polyradical

Magnetic force microscopy (MFM) was applied to study both the molecular image and the magnetic response of π‐conjugated, non‐Kekulé‐, and nondisjoint‐type poly(1,2‐phenylenevinylene) (nondisjoint refers to a molecule in which non‐bonding molecular orbitals share the same region in the molecule and a multiplet ground state is significantly stabilized) networks bearing 4‐substituted di‐tert‐butylphenoxyl moities. The polyphenoxyl radicals 1 with molecular weights of 2.6, 9.3, and 32 kDa have a substantial stability even at room temperature and in air, and molecular sizes in the nanometer range of 10, 20, and 35 nm, respectively, with a disk‐like shape. The MFM clearly shows a magnetic gradient response exactly on the position of the polyradical molecule dispersed on a graphite surface. The MFM molecular image of polyradical samples with different molecular weights and spin concentrations was examined as a nanoscale and single‐molecular‐based magnetic dot.     

一种直线感应电机的电磁场有限元分析

直线感应电机目前已经在地铁、轻轨等轨道交通中得到了很好的应用，在高速交通系统和其它一些游乐设施中也有光明的前景。本文针对正在建设中的直线电机综合测试试验台所用的直线电机，通过合理简化的方法建立了MAXWELL2一D仿真模型，同时也介绍了该类电机的结构和其传统等值电路。通过对有限元仿真结果与直线电机等效电路的计算值比较研究，发现用这两种不同方法得出的直线电机牵引力值和初级电流值非常接近，从而验证了仿真的正确性，仿真结果对今后控制系统的优化有着重要意义。     

Levitation Force Between Monolayer of Magnetic Particles and Superconducting Plane in Meissner State

We have calculated the levitation force and the interaction energy between a thin monolayer of super-paramagnetic fine ferromagnetic particles system and a large flat superconductor in the Meissner state. Both energy and force depend on the temperature and the levitation height of the monolayer. Our results show that the interaction energy and the levitation force increases as the temperature of the momolayer increases. In the limit of zero Kelvin temperature, we found that our results for the levitation force goes over to the case where all the moments of the fine-particle system are parallel to the superconductor surface, which has the lowest interaction energy.     

圆锥形接触式辐射器的研制

医疗上常用的非接触式辐射器漏能太大，远远超过国家规定微波辐射卫生标准。本文设计的圆锥形接触式辐射器漏能小，温度分布合理，有效功率增加，使用效果良好。     

型全缓冲模组内存散热器研究

随着电子技术的发展,内存器件的封装密度和功率密度都在不断提高,单位体积发热量也有所增加.为此,设计并讨论了两种新型的FB-DIMM内存散热片,利用CFD软件对其散热性能进行了模拟并给出了求解结果.此外,对两种新型散热器片进行了实验测试,并将实验结果与CFD求解结果进行了比较,两者比较吻合.分析结果表明:当环境温度为50℃时,在4 m/s的风速情况下,使用这种新型散热片,整个内存表面的温度低于80℃,可满足内存的使用要求.     

对架空电力线路中电场、磁场及辐射的探讨

随着电网建设的发展,架空线路不断增多,特别是由于规划部门对土地审批越来越严格,线路通道在很多地区已经成为影响电网建设的主要因素,因此,有必要对架空电力线路的电场、磁场和辐射进行探讨。     

柱形等离子体辐射体输入阻抗测量

通过研究等离子体作为电磁波传导媒质的基本物理原理,可知表面波激发的柱形等离子体在特定条件下,可以代替传统的金属用于构成最基本的辐射振子。针对此等离子体辐射体为有源天线的特点,结合传输线阻抗匹配的原理,设计实验对其输入阻抗进行测量,得到符合理论分析的初步结果。对等离子体作为辐射体传输电磁波的研究具有重要的参考价值。     

LED散热器热分析建模方法

针对LED散热器热分析常用的热传导分析模型与流固耦合分析模型存在适用面窄与计算量大的不足,研究了LED散热器热分析的建模方法.提出了一种可以用热传导分析模型等效简化流固耦合分析模型的方法,该方法能快速得到散热器的温度状态并能从等效换热系数h获得LED散热器所需风扇的技术参数即风扇流量,有助于风扇规格的选择.以一款LED车灯风冷散热器的热分析为例,表明提出的等效简化建模方法不仅可以提高分析计算效率,而且具有良好的实用价值.     

低阻抗辐射源的数学模型

进行电磁环境预测要解决的关键问题之一是建立实用的电磁辐射源的数学模型，本文介绍几种基于贴近场测量技术的低阻抗辐射源模型，并进行了实验验证。可用于计算、预测各种仪器、设备机箱的电磁泄漏对远区场的影响。     

一种新型肋片式散热器的热设计

本文阐述了一种新型的肋片式散热器,在强迫风冷的条件下对散热器进行了热分析计算,并验证了某高功率MOSFET功率管的结温。本文重点是散热器的理论计算。     

Magnetic Force Microscopy of Iron and Nickel Nanowires Fabricated by the Matrix Synthesis Technique

Iron and nickel nanowires are grown by the matrix synthesis technique in the pores of the track membrane fabricated based on polyethylene terephthalate (PET). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to image the pores on the surface of the specimens and determine the 3d metal nanowires in a polymer bulk. The magnetization curves of the arrays of the nanowires are obtained. Magnetic properties of the nanowires are studied by the magnetic force microscopy (MFM) methods. The influence of the interposition and magnetostatic interaction of the nanowires of the magnetic metals in the polymer membrane, as well as the magnitudes and orientation of the applied external magnetic field, on the obtained MFM images is shown. The simulation results of the MFM images are in good agreement with the experimental data.     

高温正向栅电流下Ti/Pt/Au栅SiC MESFET的栅退化机理

SiC MESFET器件的性能强烈依赖于栅肖特基结的特性,而栅肖特基接触的稳定性直接影响其可靠性.针对SiC MESFET器件在微波频率的应用中射频过驱动导致高栅电流密度的现象,设计了两种栅极大电流的条件,观察栅肖特基接触和器件特性的变化,并通过对试验数据的分析,确定了栅的寄生并联电阻的缓慢退化是导致栅肖特基结和器件特性退化,甚至器件烧毁失效的主要原因.