EM Local Heating with HF Electric Fields

Capacitor-plate applicators consisting of a pair of flat-plate electrodes, energized by a HP voltage, are utilized to induce heating inside a biological body for the purpose of hyperthermia cancer-therapy. In this paper, a theoretical analysis for such applicators is presented. A pair of coupled integral equations for the unknown total induced electric field inside the body and the charge density on the electrodes is derived and solved numerically for several different cases. The distribution of the specific absorption rate (SAR) of energy inside the body is obtained for each case. The body-electrode coupling is taken into account. A theoretical scheme for synthesizing proper potential distributions on two arrays of subelectrodes for inducing a desirable SAR ditribution inside the body is also developed. Using such arrays of subelectrodes, the excessive heating at the fat layer of the body may be avoided. An experiment has been conducted to test the theory.     

短波组网技术探讨

讨论了短波组网的特点和要求,综合了几种国外短波网络的体系结构、设计方案,以及用于短滤网络的应用技术,并对中国进一步发展短波网络技术提出建议。     

磁性随机存储器中的电流磁场分布模型

根据磁性随机存储器(MRAM)设计的实际需要,建立了MRAM中相互垂直的字线和位线电流所产生的磁场的解析分布模型。利用该模型讨论了存储单元与位线间距离(d1),字、位线宽度(w)及字、位线厚度(t)对存储单元自由层表面磁场分布的影响。结果表明,d1或w增大时,自由层表面磁场的强度及非均匀程度都减小。t增大时,自由层表面磁场的强度及非均匀程度都增大。其中d1对磁场分布的影响程序是最大的。该模型为MRAM更精确的器件模拟及器件结构的优化设计工作提供了必要的基础。     

以电子方式产生旋转磁场

正医疗、电磁搅拌器、感应加热等许多应用都需要旋转磁场,而你可以把多个永磁体连接到直流电机,来产生这种磁场。这种方法涉及一些问题,比如噪声,以及需要维护运动零件。本例介绍了如何在不使用机械元件的前提下,利用微控制器和全桥驱动器来产生可变磁场。该方法无需维护,不会磨损,并提供高精度的速度控制。但它需要大型磁芯     

Metalforming with Pulsed Magnetic Fields

Strong, short-duration magnetic fields may be used for direct forming of metal parts. Since the energy for forming is imparted to the workpiece solely through the magnetic field, many unusual capabilities and applications exist for the process.     

Magnetic Fields of Twisted-Wire Pairs

On the basis of an expression given by Buchholz for the magnetic-vector potential for an infinitely long twisted-wire pair, the expressions for the external component-flux densities in cylindrical coordinates have been developed. These expressions checked very well with data obtained in the proximity of precisionwound twisted-wire pairs. A generalized graph for various radii and pitch lengths has been developed to enable the design engineer to quickly predict the strength of the magnetic field for all three spacial components at distances in the proximity of a twisted-wire pair.     

Microwave and Millimeter Wave Experimental Technique and Equipment for High-Temperature Measurements of Superconducting Thin Films Surface Impedance in Strong Magnetic Fields

An experimental technique for the surface impedance measurements of high-temperature superconductor's (HTS) as well as correspondent experimental setup is considered. The method is based on the use of an optimized volume copper cylindrical resonator operating on the H₀₁₁-mode, in which the HTS-film substitutes one of the plane walls of the cylinder. The ideas realized in the setup allow us to obtain the best accuracy when measuring the surface impedance within a wide microwave frequency range.     

Em Local Heating with HF Electric Fields (Comments)

The above paper recently described a synthesis procedure that is intended for use in designing multisection capacitor-plate applicators for treatment by hyperthermia. The distribution of potentials on the subelectrodes is determined in order to obtain a specified pattern of energy deposition. While the derivation in that paper appears to be sound, considerable care must be used if the procedure is to be applied for the design of a practical applicator for use in patient treatment.     

HF RFID Reader Antenna with Loop Switch for Avoiding Magnetic Coupling

This paper studies the magnetic coupling between two adjacent loop antennas that are parallel to each other in a plane and presents a new practical method to avoid the resulting magnetic coupling interference. The study focuses on the high frequency radio‐frequency identification (RFID) system for casino applications, where several loop antennas are closely built into a game table to monitor gaming chips. In this case, neighboring loop antennas may severely interfere with each other by magnetic coupling, which leads to the malfunction of the RFID system. In this paper, we present a practical loop antenna with a new loop switch circuit for avoiding magnetic coupling. The loop switch circuit is integrated with a matching circuit and automatically operated by using an interrogating signal from a reader. We verified the validity of the proposed design by showing that an RFID reader with the proposed antenna can exactly and separately read the gaming chips placed on the different betting zones of a game table.     

An Electromagnetic System for Studying the Responses of Aquatic Organisms to Weak Electric and Magnetic Fields

Recent evidence suggests use of electric and magnetic cues as orientational aids to long-distance migration by fishes. A simple laboratory apparatus is described which accurately reproduces the electromagnetic fields an aquatic organism might naturally experience.     

Loop-Induced Magnetic Fields with Negligible Side-Lobes

In schools for the hard-of-hearing where adjacent classrooms are equipped with non-carrier induction loop systems, it is necessary to realize a geometric discrimination between the classroomfields. One approach to reaching the required 24 dB per meter rolloff at the boundaries is the orthogonal field principle reported first in 1965 by de Boer, Bosman and Joosten (ref. 2, 3, 4). In this paper a method is described and results are given for an heuristic development of this principle in the case of classrooms about 8 m in length with permissible roll-off ranges of 2 m. It is shown that it is also possible to discriminate in a vertical direction if a secondary field at the ceiling is used. The heuristic approach achieves very good results in this case and overcomes the mathematical difficulties arising when the field is calculated analytically.     

一种精确的图象边界扩展方法

本文提出一种基于正交小波滤波器组的精确图象边界扩展方法，它能有效地克服传统扩展算法中存在的重构图象边界失真的问题，并能获取较高的压缩比，实验结果表明，本文的方法有着非常良好的效果。     

双强耦合场驱动下的探测吸收光谱

在具有耦合-探测结构的Λ型三能级系统中引入另一强耦合场,形成双强耦合场作用下的Λ型三能级系统。通过求解系统的密度矩阵方程,研究了探测吸收谱的特性。结果表明,当两个耦合场的拉比频率相等,一个共振作用于跃迁能级而另一个以一定的失谐量作用于跃迁能级时,系统的探测吸收谱呈现出多峰,即多个Aulter-Townes双峰结构。给出了吸收峰的位置与耦合场的作用强度和频率失谐量之间的定量关系,并用缀饰态作出准确的解释。     

An on-line adaptive beamforming capability for HF backscatter radar

An adaptive-array beamforming capability has been implemented on-line in an existing over-the-horizon (OTH) backscatter radar. Inputs to the beamformer consisted of signals from eight 32- element subarrays of the 256-element, 2.5-km-long receiving array at the Wide Aperture Research Facility (WARF) located in California. Both conventional and adaptive beamforming were performed prior to the usual range/Doppler analysis used to extract radar targets from noise and clutter. The GriffithsP-vector algorithm, a recursive, time-domain adaptive technique, was implemented in all-digital fashion using fixed-point arithmetic on a 16-bit minicomputer. Desired signals utilized were aircraft targets and a fixed, ground-based radar repeater simulating a moving target, while unwanted signals were other-user interference and signals from a separate ground-based radar repeater. It was found that adaptive rejection of unwanted signals was dependent on pointing-angle alignment and that rejection was often increased by removal of the clutter by moving target indicator (MTI) filtering prior to adaptation. For some conditions, Doppler broadening can he produced by the time modulation imposed by continuous adaptation, unwanted-signal rejection with the adaptive beamformer is variable, but side-by-side comparisons obtained at WARF show that adaptive beamforming can reject off-azimuth signals up to 20 dB better than conventional beamforming with a -25 dB Dolph taper.     

磁场中准二维强耦合磁极化子的性质

采用线性组合算符和改进的LLP变分法,研究了磁场中无限势垒量子阱内电子与界面光学声子强耦合、与体纵光学声子弱耦合系统的基态,得到了磁极化子的振动频率和自陷能随量子阱宽和磁场变化的规律.对CdF2/AgCl量子阱进行了数值计算,结果表明,磁极化子的振动频率和自陷能随阱宽的增加而减小,随磁场的增加而增大,但不同支声子与电子和磁场相互作用对磁极化子的振动频率和自陷能的贡献大不相同.此外,对以上现象进行了分析和解释.     

Interaction of Magnetic Fields and Ferromagnetic Shields

An analytic procedure is developed for the purpose of determining the effectiveness of ferromagnetic shields in shielding against magnetic fields. The basic approach is to separate the magnetization relation of a ferromagnetic material into regions in which each region is characterized by a constant permeability. Maxwell's equations are then solved in each time-varying geometric region (which correspond to the regions of the magnetization relation) and the solutions are matched at interfaces. This procedure permits solutions for nonlinear shielding problems to be readily obtained using linear techniques.     

A Novel Non-Equidifferent Optical APPM Mapping Scheme for Strong Turbulent Atmospheric Channel

An optical Amplitude and Pulse Position Modulation(APPM) mapping scheme for strong turbulent atmospheric channel is proposed to optimize Bit Error Rate(BER) performance.In this scheme,a nonequidifferent amplitude series is designed based on quantitative BER analysis of the specific A×M APPM demapping procedures containing time slot selection and amplitude decision in selected time slot,which are different from traditional ones.Simulation results of 4×4,4×8 and 4×16 APPM show 4,3.4 and 6.9 d B SNR gain against traditional APPM scheme respectively.Thus significant BER performance improvement is achieved which helps to enhance reliability of freespace optical communication systems.     

强磁场环境下音频传输的实践与经验

本文通过对《蜘蛛侠爬福塔》活动中音频传输的设计思路和实践经验的介绍,分析了在强磁场环境下进行音频传输可能遇到的问题及解决方法。     

Mapping of North Atlantic winds by HF radar sea backscatter interpretation

This work presents preliminary results on attempts to map winds of a storm at long range (500 to 1000 nmi) over a large area (10^{5}mi²) in the North Atlantic from the U. S. Naval Research Laboratory, HF radar research facilities at Chesapeake Beach, Md. [1] It appears that the short time response of the sea surface to local winds can be mapped by the analysis of a matrix of range-azimuth records containing frequency power spectra of HF radar signals backscattered from the sea surface via the ionosphere. This paper presents such a map based upon the ratio of the strengths of the first-order contributions to the backscatter spectrum (the approach-recede first-order Bragg lines) and is compared qualitatively with a U. S. Weather Bureau map of the area.     

Tests for Human Perception of 60 Hz Moderate Strength Magnetic Fields

After preliminary experiments that pointed out the extreme cleverness with which perceptive individuals unintentionally used subtle auxiliary clues to develop impressive records of apparent magnetic field detection, we developed a heavy, tightly sealed subject chamber to provide extreme isolation against such false detection. A large number of individuals were tested in this isolation system with computer randomized sequences of 150 trials to determine whether they could detect when they were, and when they were not, in a moderate (7.5-15 gauss rms) alternating magnetic field, or could learn to detect such fields by biofeedback training. In a total of over 30,000 trials on more than 200 persons, no significantly perceptive individuals were found, and the group performance was compatible, at the 0.5 probability level, with the hypothesis that no real perception occurred.