Electromagnetic field optimisation procedure for the microwave oven

This article introduces one method for optimising a microwave oven using microwave CAD technology. The precision model of a microwave oven cavity is created by high-frequency electromagnetic simulation software, and the electric characteristic parameter of the materials are set in the cavity so the simulation model is very close to a practical oven cavity. A new experimental set-up consisting of a multimode microwave cavity, a dielectric parametric test system, a vector network analyser, a microwave power source (magnetron) and a thermo-graphic camera has been built and tested. Comparing the simulation result with the experimental measures (phase polar and power loss), their total properties are consistent. It is proved that the method presented here is practical and useful. So optimisation of the oven design is easily done by modifying the cavity model.     

Electromagnetic field photonic sensors

In this paper, we review the different configurations proposed for electromagnetic field optical sensing. Intrinsic and extrinsic optical fiber sensors for electric and magnetic field measurement are examined, including those realized jacketing the fiber by magnetostrictive, conductive, electrochromic and polymeric materials and those measuring induced strain by magnetostrictive, electrostrictive and piezoelectric transducers. Extrinsic optical fiber sensors exploiting magneto-optic, electro-optic and Joule effects are also presented.Moreover, integrated optical electric and magnetic field sensors in which microwave signal provided by an antenna modulates the optical signal generated by an optical source are reviewed. Finally, active and coupled resonators based on electric field sensors are investigated.     

浅论通信领域内的电磁兼容

0引言 随着科学技术的进步和发展,人们在日常生产生活中使用的电子、电气设备的种类越来越多,电子电气设备使用的频段越来越高,电子设备在运行的时候,往往产生一些人们不需要的电磁能量,这些能量通过辐射、传导的方式向外界传出来会影响其他设备或系统的工作.     

红外光谱法研究静磁场对大鼠脑组织的影响

电气工业的发展使得人们生存的环境中充满了各类频率的电磁污染,为了探讨静磁场可能产生的生物学效应及其发生机制,从实验上研究了0.17 T静磁场曝露作用30天后对于大鼠脑组织红外光谱特征的影响,实验结果显示实验组1549 cm-1附近的酰胺Ⅱ带吸收峰有较为明显的红移现象,在1635 cm-1处为蛋白质酰胺Ⅰ带峰位置有较大的差异,另外,利用二阶导数谱分析了实验组与对照组在分子结构上存在的差异。这些变化可以反映脑组织在静磁场曝露作用前后组成成分的变化,说明傅里叶变换红外光谱方法是研究电磁场不同生物效应的发生机制的一种有效手段。     

Electromagnetic field near rail guns

The field in the neighborhood of an electromagnetic rail gun is computed for the case of constant current. The analysis centers on the Westinghouse EMACK launcher in which two rails of 2-m length carry a peak current of 2.1 MA, while a peak power of over 10 GW is delivered to the rails. Expressions are derived for electric field strength and magnetic flux density as functions of gun parameters. These formulas can be used to compute the electromagnetic pulse produced by a rail gun of any given characteristics     

《电磁场工程应用》高阶课堂探索

建设有深度、有难度、有挑战度的“金课”,是每个教师都面临的挑战。以《电磁场工程应用》课程的“电导和接地电阻”为例,介绍其高阶课堂的构建过程。在课程教学中,采取线上线下混合式教学模式。在线下课程中,采取“思考”+ “讨论”的“问号课堂”,激发学生思考和讨论。采取适当“吊胃口”的方式,达到让学生“既疑又懂”的效果,尽量做到“思中学”、“做中学”,培养学生主动学习和主动实践能力。     

Electromagnetic field of an infinite helical sheath

The relevant fields of an infinite helical sheath, produced by a current distribution on the helical surface, are obtained for the case in which the internal medium is different from the external one.     

Electromagnetic field plot of an inductive window by the momentmethod

A moment method is used to plot the electromagnetic field of an inductive window in a TE₁₀-mode rectangular waveguide. Green's dyadic functions are derived based on Tai's approach, which is a modified form of Hansen's vector wave functions. Based on the computed electric fields, the S matrix and the equivalent aperture reactance of the waveguide window are calculated. This calculation agrees with the previously published closed-form results of N. Marcuvitz (1964)     

Electromagnetic field estimation in the vicinity of panel antennasystem for FM and TV broadcasting

The paper presents an approximate numerical technique for the estimation of the EM field distribution in the vicinity of broadcast FM and TV antenna systems. This technique is needed to estimate the health hazards and other environmental problems. It is based on the geometrical factors of the system, the directional properties of the panel used, the power and voltage phases supplying the panels and the electrical parameters of the ground     

Electromagnetic energy exposure of simulated users of portablecellular telephones

Describes a method to quantify the RF exposure of the users of portable cellular phones in terms of specific absorption rate (SAR). The method involves a robotic system to accurately position an isotropic E-field probe within equivalent biological tissue. The user of cellular phones is simulated by a simple human model (a phantom) consisting of a thin shell of fibreglass filled with a liquid having the complex dielectric constant of human brain tissue. The authors present the results of the dosimetric assays conducted using current and previous models of cellular telephones. The peak SAR values detected using the measurement method described are below the limits recommended by the National Council for Radiation Protection and Measurements (NCRP) Report 86 for the protection of humans exposed to RF electromagnetic energy     

Electromagnetic field behavior near homogeneous anisotropic wedges

The behavior of electromagnetic fields in the vicinity of homogeneous anisotropic wedges is investigated. An extensive analytical treatment is presented for the fields near the tip of the wedge in the static limit. This can be carried out by first allowing the propagation parameter to vanish and then by solving the resulting Laplace-type equation to determine the local distribution of the electric and magnetic fields, which can be found from two transcendental equations. The roots of these equations govern the radial dependence of the field close to the tip and, hence, a graphical representation of their solutions is introduced to illustrate the circumstances under which the fields exhibit singular behavior. Numerical case-studies are presented along with the results obtained by using the static approximation to the dynamic problem. The near fields are calculated so that their radial dependence in the azimuthal plane can be compared to that extracted from the static power law     

Electromagnetic field measurements a millimeter wave linearaccelerator

Perturbational field strength measurements suitable for use on a proposed 120-GHz 50-MeV electron linear accelerator are described. The measurements are used to determine the R/Q of the device, where R is the shunt impedance. The perturbation is achieved by the use of hollow metallic cylinders with diameters ranging from 25 to 127 μm which are approximately 500 μm long. The cylinders were fabricated by sputtering aluminum through a shadow mask onto silica optical fibers as well as nylon surgical thread. The perturbational “form factors” for such a geometry are experimentally determined using a pillbox cavity. The measured values for the form factors are compared to theoretical estimations, which result in simple analytical expressions. The measured form factors are also compared to values calculated from a finite difference model of the perturbing object. The R/Q for various accelerating modes is measured on a 12-GHz model of the 120-GHz structure. Results are compared to predictions from a finite difference model of the accelerating structure     

Electromagnetic field computation using a hybrid computer

A hybrid computer approach for obtaining approximate closed-form solutions for boundary value problems satisfying the Laplace or Poisson equations under Dirichlet boundary conditions is investigated. The results are compared with those obtained by a digital machine.     

A system for the exposure of small laboratory animals to a 25-mT60-Hz alternating or traveling magnetic field

A versatile exposure system which can be used to investigate the effects of a 60-Hz alternating magnetic field or traveling magnetic field on small laboratory animals is described. Special attention was given to the design of the electric circuit to simplify the supply requirements and to keep the overall current to a minimum. A magnetic field having a flux density up to 30 mT (300 G) can be generated, and a traveling magnetic field is obtained by reconnecting the coils to a three-phase supply. The total magnetic field due to the currents in the three coils used in the exposure system is analyzed. A computer program was written to evaluate the magnetic field in the region where the animals are located. The difference observed between measured and computed values is attributed to the representation of the multiturn, multilayer coils by equivalent single-turn coils     

Electromagnetic field intensity triggered micro-biopsy device for active locomotive capsule endoscope

For an active and precise diagnosis, we developed an active locomotive intestinal capsule endoscope (ALICE), which can be wirelessly driven and controlled using an electromagnetic actuation (EMA) system. Since then, there has been a need to develop a biopsy device integrated into ALICE which can take a biopsy sample inside the gastrointestinal tract for a historical analysis of cancer disease. Toward this goal, this paper proposes a smart-triggered biopsy device for the ALICE using a micro-reed switch, where the integrated micro-reed switch is turned on using a strong magnetic field, and the biopsy device mechanism is activated by a micro-reed switch. To execute the biopsy process, first, the ALICE with the biopsy device is driven by an EMA system, where a moderate intensity magnetic field is used for driving the ALICE to reach a target region on the intestinal wall. After that, by increasing the magnetic field above a critical value, the ALICE is pushed hard against the target lesion, the micro-reed switch is turned on, and the biopsy device is triggered. The biopsy process, therefore, is totally wirelessly controlled by the external magnetic field of the EMA system, without an additional controller module. The prototype of the biopsy device, with dimensions of 12 mm in diameter and 5 mm in length, was integrated into the ALICE and the prototype of the ALICE, with the biopsy device having dimensions of 12 mm in diameter and 32 mm in length. The working principle and mechanism of the proposed biopsy device are introduced and the feasibility of ALICE with the biopsy device is demonstrated through in-vitro experiments.     

磁偶极子电磁场计算及仿真

在对称线圈上施加强脉冲电流,在脉冲电流的激励下,线圈中产生感应脉冲磁场,从而实现同极性磁场撞击.在撞击过程中,磁能会以一种波的形式激发出去,从而产生激磁波.激磁波是一种磁性波,其能量主要通过磁场的变化进行传递.利用有限元的方法对对称线圈的内部外部分别进行仿真,讨论并分析了点磁场在空间和时间上的变化.     

Electromagnetic field inside a surface current distribution

The electromagnetic field and a generalised electric Green's dyad, when the field point is inside a surface current distribution are derived. The Green's dyad is represented by the sum of the dyadic Green's function in free space and a source dyad determined by the shape of the principal area that surrounds the singularities of the Green's function.<>     

Electromagnetic random field models for analysis of coupling inside mode tuned chambers

The statistics of interference sources, induced by the electromagnetic fields of a mode tuned chamber (MTC), in electronic equipment is computed from the field's spatial covariance operator and a deterministic current distribution on the system under test. An example shows that the computed results, obtained with two canonical random field models, compare very well with measurements. In addition, a new and interesting relation between the variances of two-port S-parameters is established, which can be used to detect bad stirring in MTC.     

雷电磁场探测仪器的设计与研究

设计制作了一种用于雷电磁场探测的磁场测量天线系统。该测量系统分为天线部分、数据处理部分和数据采集部分。利用函数发生器以及示波器对设计的数据处理电路进行标定后发现,电路能够不失真地放大天线部分感应的微弱信号,利用ICGS实验冲击平台并配合Tektronix TDS 2022对整个测量系统进行模拟雷电采集实验后发现,该测量系统能够很好地反应雷电的磁场变化。     

Electromagnetic field analysis of a four-wire anechoic chamber

The electromagnetic field characteristics and plane-wave generating ability of a parallel four-wire anechoic chamber which is to be operated in the VHF range is analyzed. The analysis considers three cases: the first is a four-wire chamber when only a thin layer of absorber material covers the chamber walls, the second is a four-wire chamber when only free space surrounds the four wires of the system, and the third is a four-wire chamber when a thick layer of absorber material covers the anechoic chamber walls. The three cases are analyzed by a variety of mathematical methods including the method of moments, waveguide theory, and a finite-difference time-domain method. Numerical results for the propagation constants and electromagnetic fields that are generated in the chamber in the three cases are presented