磁场测量接收参数变换实例

以GB/T 19954中的磁场测量为例,介绍了测量接收参数的设置过程,给出了磁场测量天线系数的定义及来源。依据分贝的定义及磁通密度与磁场强度的关系对标准限值的单位进行变换,又从使用的角度对计量证书中的天线系数进行了变换,从而解决了接收参数设置过程中会遇到的测量单位不统一和设置困难问题。     

均匀外磁场中铁质球体系统磁场的镜像解析解

均匀外磁场中铁质球体系统磁场的计算一般是比较困难的,这是因为铁质球体之间的相互磁化比较难处理.从点磁荷与磁介质球系统中的镜像法出发,对磁介质球中的镜像线磁荷进行简化等效,推导出铁质球体系统中镜像磁偶极子和镜像磁荷的表达式.然后计算铁质球体之间各阶相互磁化而产生的附加磁场,进而求出铁质球体系统磁场的镜像解析解,并分析讨论了镜像解析解最大阶数的选择.仿真实验结果表明,镜像解析解的误差非常小,且适用于各种相对磁导率下铁质球体系统磁场的计算.     

A Study of the Interaction Between Implanted Pacemakers and the Radio-Frequency Field Produced by Magnetic Resonance Imaging Apparatus

Specific absorption rate (SAR) and temperature increases produced inside a thorax model by an MRI apparatus equipped with a birdcage antenna operating at 64 MHz have been studied both experimentally and numerically. Considering a pacemaker (PM) equipped with a unipolar catheter inserted inside the thorax model, peak SARs averaged over 1 mg between 240 and 6400 W/kg, depending on the catheter section and length, on its position inside the phantom, and on field polarization have been obtained close to the catheter tip. On the other hand, the average SAR in the whole thorax is not influenced by the presence of the PM. Temperature increments from 0.6degC to 15degC have been obtained for 6-min MRI investigations with the lowest values when the radio-frequency (RF) magnetic field is linearly polarized along a direction perpendicular to the implant plane.     

Propagation of Waves in a Plasma in a Magnetic Field

The propagation of electromagnetic waves in a plasma in a magnetic field as given by the Appleton-Hartree theory is discussed in terms of the wave normal surfaces instead of the more conventional propagation vector plots, and the "ordinary" and "extraordinary" waves are defined in terms of their polarizations instead of using a continuity argument. This gives a different picture of "a wave" which has some advantages. In particular, "whistlers" become obvious, as are regions of high reflection and high absorption. The Appleton-Hartree theory is then extended to include the effect of electron temperature, and this results in a third wave whose velocity is of the order of electron thermal motions.     

无引导磁场电子注的空间电荷波

本文导出了无外磁场电子注在等离子体约束下其上传播的空间电荷波波动方程,详细讨论了该条件下的波特性,并对等离子体频率降低因子进行了分析．研究表明,等离子体填充状况对空间电荷波性质影响甚大,选择等离子体填充因子可对空间电荷波性质进行适当的控制．     

优化极靴的微波炉磁控管磁场分析

利用MAFIA静态磁场仿真模块对微波炉磁控管磁路进行仿真分析，并通过对比实测结果改进模型，主要分析缩短极靴后的磁场变化，然后制作了样管，测试并比较性能参数，在保证输出功率和效率的前提下，达到节约成本的目的。     

Nonreciprocal Wave Propagation in Semiconductor Loaded Waveguides in the Presence of a Transverse Magnetic Field

Approximate solutions for the complex propagation constant in semiconductor loaded waveguides are obtained by expansion of the fields in terms of a finite number of the empty waveguide modes. Solutions are obtained for the case of partial loading in the narrow dimension of the guide, which explicitly exhibit the non-reciprocal effects observed in the presence of a transverse magnetic field. Coupling between the TE/sub 10/ and TM/sub 11/ empty waveguide modes is shown to explain qualitatively the observed experimental effects. Good quantitative agreement with experiments using Si samples is obtained.     

Propagation of Electromagnetic Waves in Rectangular Guides Filled with a Semiconductor in the Presence of a Transverse Magnetic Field

The characteristics of electromagnetic waves propagating in a semiconductor filled rectangular waveguide in the presence of a transverse magnetic field are studied. It is shown that only TE mode waves having y-independent field components (y being the direction of the steady magnetic field) and anomalous modes having all six field components can propagate. The propagation constant of waves characterized by a sinusoidal y dependence of fields is derived. Asymptotic expressions for the fields and the propagation constant are then obtained for the limiting case of a small external magnetic field and some recent experimental results are analyzed in this context.     

IEC61000-4-8中矩形感应线圈磁场均匀性缺陷的分析

首先推导了矩形感应线圈的磁感应强度空间分布解析表达式,通过数值仿真分析磁感应强度沿各轴向的变化趋势和磁场空间分布特性,指出现有标准定义的3 dB试验区域内存在12个磁感应强度基准偏差超出±3 dB的缺陷区域,并对分析结果进行实验验证。     

Thermodynamic Properties of Gapped Graphene in the Presence of a Transverse Magnetic Field by Considering Holstein Phonons

Using the Holstein model, the thermodynamic properties of gapped graphene in the presence of electron–phonon (e–ph) coupling and a transverse magnetic field are investigated. In particular, we have obtained density of states (DOS), electronic heat capacity (EHC) and magnetic susceptibility (MS) of graphene, for which carbon atoms are substituted by boron and nitride atoms in the presence of Holstein phonons and a transverse magnetic field within the Green’s function approach in order to investigate the dynamic of Dirac fermions. To find the electronic self-energy due to e–ph coupling and the substituted foreign atoms, the self-consistent second order perturbation theory has been implemented. The band gap decreases with magnetic field and e–ph coupling. Also splitting of the quantum states (energy levels) due to the magnetic field is observed as double peaks in DOS (Van Hove singularities). As a remarkable result, EHC and MS are decreased due to the increase of scattering rate between electrons, an applied magnetic field, and e–ph coupling.     

有限磁场中等离子体通道天线的辐射特性分析

为了弥补现有高功率微波武器辐射天线的不足,提出了等离子体通道天线(PCA),研究了该天线的辐射特性.根据PCA的工作原理,将PCA等效为电子在横向旋转、轴向漂移的均匀冷磁化等离子体束,且认为该等离子体束的横截面为沿轴向不改变的圆形;推导出了一般性天线的辐射方向函数;结合麦克斯韦方程和本构关系,得出了PCA的色散方程,求出PCA的表面波波矢.重点讨论了PCA的辐射特性随等离子体密度、天线长度、半径及纵向速度的变化,得出一些有益的结论,为PCA的实现打下坚实的理论基础.     

Measurements of the Field Strengths on Offshore Oil Platforms for Assessing Radio-Frequency Hazards with Electroexplosive Devices

Radio-frequency (RF) hazards can arise during the handling and arming of explosives used in the offshore oil industry if sufficient RF energy is coupled into the electroexplosive device (e.e.d.) used for detonating the main ordnance. Within the oil industry, it is standard practice to deal with this potential hazard by employing radio-silence procedures which vary widely from company to company. The measurements presented within this paper have provided detailed information on the RF environment of two oil production platforms in United Kingdom North Sea waters. The measurements indicate where the potential hazards are most serious, hence, where more detailed studies are required, and where relaxations in radio silence may be applied.     

Effect of Finite Rise Time on the Strength of the Magnetic Field Generated in a Switched Plasma

The effect of a magnetized transient plasma on a circularly polarized source wave, when the rise time of the electron density profile is comparable to the source wave period, is considered. The H-formulation Green's function is developed to study the effect of a finite rise time on the generation of a wiggler magnetic field.     

放电等离子体中XeI准分子的形成过程

研究了Xe/I2 混合气体 (气压 70～ 1330Pa)在直流辉光放电情况下XeI 准分子的形成过程 ,得到了XeI 准分子在 2 40～ 2 70nm波长范围内的荧光发射谱。并对XeI (B→X)跃迁谱线强度随混合气体压力的变化进行了实验研究 ,发现气压为 333Pa时荧光最强 ;此条件下 ,放电等离子体的电子温度为 13 2eV ,表明低气压放电等离子体中主要反应通道为快电子碰撞Xe使其跃迁至 3 P ,随之与I2 碰撞形成 XeI(A ,B ,C)。     

Parameters to Define the Electron Beam Trajectory of a Double-Tapered Disc-Loaded Wideband Gyro-TWT in Profiled Magnetic Field

In the method of tapering the cross section of the interaction structure for broadbanding a gyro-TWT, the different portions of the interaction length of the tapered-cross-section waveguide become effective for different frequency ranges if the magnetic field and beam parameters are profiled to maintain the condition of electron cyclotron resonance throughout the interaction length. In the present paper, the study of profiling the magnetic field and beam parameters in steps of the stepped analytical model of a double-tapered disc-loaded circular waveguide was made throughout the steps of the model. In the observed profile, the magnetic flux density in a typical step relative to its value in first-step decreases from first-step (gun-end) to end-step (collector-end) of the model considering the up-tapering schemes, in which structure parameters increase from gun-end to collector-end. Also, the transverse beam velocity in a typical step relative to its value in first-step decreases from gun-end to collector-end. However, the Larmor radius in a typical step relative to its value in first-step as well as the hollow-beam radius in a typical step relative to its value in first-step, both increase from gun-end to collector-end in the model considering the up-tapering schemes.     

超强激光与等离子体作用产生自生磁场的新机制

应用多光子非线性Compton散射模型和粒子模拟程序,研究了Compton散射对等离子体中自生磁场的影响,提出了将超强入射激光脉冲和Compton散射光形成的耦合光作为形成自生磁场的新热电机制,给出了自生磁场的修正方程,并进行了仿真实验验证。结果表明:入射激光的ω0t350时(ω0和t分别是入射激光的圆频率和脉冲宽度),电子密度发生明显变化,这是由于散射使质子与电子碰撞频率增大,能量交换加快,超热电子获得更高能量,从而带动更多质子加速的缘故。自生磁场空间分布范围和强度增大,这是由于散射使等离子体碰撞频率及电子的温度和密度梯度增大的缘故。自生磁场先较快增加后指数增长,到达正饱和后缓慢减小,最后达到负饱和状态,形成对称结构。自生磁场最大值为5.3×103T,比散射前强。这是由于散射使更多粒子发生了二、三阶电离,更多超热电子形成了更强的电流,最后趋于稳定的缘故。强自生磁场处温度梯度最大,且沿y方向,电子有效温度为0.61 MeV,比散射前更接近理论结果0.63 MeV,这是散射对电子温度贡献的结果。     

用火花电阻计算高压毫微秒脉冲放电参量

本文用火花电阻公式研究了高压毫微秒脉冲参量（脉冲幅值、前沿、宽度）与储能电容的关系。结果表明，用火花电阻等效亚纳秒脉冲放电管击穿后的状态是合适的。     

Structuring Copper in the Plasma Medium of a High-Frequency Discharge

Currently, copper is a priority material for the formation of interelement connections and distributions in silicon ICs. In addition, copper is widely used to create flexible printed circuit boards and multilayer hybrid ICs. We used freon R-12 (CCl₂F₂) as a plasma-forming medium for etching copper in this work. Freon R-12 plays an important role in the plasma etching industry by providing the technological parameters required in the process. In this article, an experimental study has been carried out of the features of the interaction of the copper surface with freon R-12, as well as the influence of the treatment time and external plasma parameters (temperature, displacement power, consumption power, gas pressure) on the quality of the near-surface copper layer.     

“电磁场与电磁波”课程教学中的归纳与演绎

本文讨论了提高＂电磁场与电磁波＂课程教学效果的两种教学方式,即演绎和归纳教学。演绎教学始于从一般到个别的过程;归纳教学则相反。我们比较了两种方法在电磁场教学过程中的特点和应用,除从顶而下与至底而上的本质区别外,归纳教学具有启发性,培养学生的探索创新精神;演绎教学从一般的实验事实和科学假设出发,培养学生的逻辑思维能力。它们可以同时应用在电磁场课程的教学中,相互渗透,互为补充。