ELF Coupling to Spherical Models of Man and Animals

The induced fields, currents, and power absorbed by spherical models of humans or animals when exposed to extremely low frequency (ELF) electromagnetic fields are calculated. Spherical models can be expected to provide values of the right order of magnitude. The induced fields are a sum of the quasistatic solutions for a sphere irradiated by a uniform electric and magnetic field. Calculations are provided for ELF fields emanating from the proposed Navy's Sanguine antenna and extra high voltage (EHV)/ultra high voltage (UHV) transmission lines proposed by the utility industry. The question of biological hazards from exposure to fields of these systems is also considered.     

Electric field probes--A review

Electric field probes consisting of a dipole antenna, RF detector, nonperturbing transmission line, and readout device have been implemented in a variety of ways. Three orthogonal dipoles are generally used in anE-field probe to provide a response which is nearly isotropic for all polarizations of the incident field. Diode detectors have been used with electrically short or resistivity loaded dipoles to produce very broadband devices (0.2 MHz to 26 GHz). Thermocouple detectors are used to provide true time-averaged data for high peak-power modulated fields. Optical fibers, together with a suitably modulated light source, may be used to form a wide-band nonperturbing data link from the dipole and detector to a remote readout. Application ofE-field probes range from the measurement of fields in living animals exposed to nonionizing radiation to the measurement of fields in air for electromagnetic compatability or radiation safety purposes. Probes are available that can measure field strengths from less than 1 V/m to over 1000 V/m (rms).     

SLF/ELF水平电偶极子在地-电离层波导中的场

在非理想导电地面与电离层条件下,导出了SLF/ELF水平电偶极子在球形地-电离层壳体中产生的电磁场的球谐级数表达式,采用一种加速收敛算法,算出了波导中的电磁场分布.根据计算结果,在SLF频段,地面与电离层之间的电磁场可理解为两个"行波"的叠加,且与SLF频段的球面二阶近似算法计算结果吻合很好.在ELF频段,壳体中的电磁场是驻波,其频率变化规律能正确反映出"舒曼"谐振现象.     

地下SLF/ELF水平电偶极子在球形地-电离层中产生的场

在非理想导电地面与电离层条件下,导出了地下SLF/ELF水平电偶极子在地上、地下及电离层中产生的电磁场的球谐级数表达式.并提出了一种加速收敛算法,算出了大气层及电离层中的电磁场分布.计算结果表明:地下几十公里的水平电偶极子产生的场除了增加了一个固定衰减外,与地面上的水平电偶极子产生的场分布完全相似,它产生的电磁场可理解为电波首先垂直地透过土壤,然后在地一电离层腔体中传播.在SLF频段,地一电离层空腔中的电磁场可理解为两个"行波"的叠加.在ELF频段,空腔中的电磁场是驻波,其频率变化规律能正确反映出"舒曼"谐振现象.     

CAD-Oriented Model of a Coplanar Line on a Silicon Substrate Including Eddy-Current Effects and Skin Effect

Silicon technologies are now widely used for RF applications. Due to the substrate and conductor conductivity, losses and magnetic coupling affect the signal propagation in transmission lines. We propose an equivalent scheme for a transmission line taking these phenomena into account. All the parameters are analytically extracted from measurements. The magnetic coupling, including eddy currents, are described as series elements. They are affected by skin effects. The electric losses are described as parallel elements. They depend on the different layers that the electric field lines meet.     

SLF/ELF垂直电偶极子在理想导电地-电离层中的场

在理想导电地面与电离层条件下,我们导出了SLF/ELF垂直电偶极子在球形地-电离层壳体中产生的电磁场的球谐级数表达式,并提出了一种加速收敛算法。利用此算法分别算出了电场分量随传播距离、高度及工作频率的变化,所得计算结果与Barrick方法所得结果基本吻合。由于地面和电离层没有吸收损耗,地面与电离层之间产生的场是＂驻波＂,在ELF频段,其频率变化规律能正确反映出＂舒曼＂谐振现象。     

垂直电偶极子在地-电离层波导中场的球级数解

在非理想导电地面与电离层条件下,我们导出了ELF/SLF垂直电偶极子在球形地-电离层壳体中产生的电磁场的球谐级数表达式,采用一种加速收敛算法,算出了波导中的电磁场分布.根据计算结果,在SLF频段,地面与电离层之间的电磁场可理解为二个"行波"的叠加,且与SLF频段的球面二阶近似算法计算结果吻合很好.在ELF频段,壳体中的电磁场是驻波,其频率变化规律能正确反映出"舒曼"谐振现象.     

Moment method analysis of the electric shielding factor of aconducting TM shield at ELF

This paper presents an integral equation and method of moments (MM) solution to the problem of TM transmission by a metallic conducting shield at extremely low frequencies (ELF). To obtain an accurate and efficient solution, the equivalent volume polarization currents representing the shield are expanded in terms of physical basis functions, corresponding to two planewaves propagating normal to the surface of the shield. ELF approximations are used to obtain closed form expressions for certain crucial elements in the MM matrix equation where extreme accuracy between the relative magnitudes of self and mutual impedance terms are required. Numerical data will illustrate that despite the fact that the equivalent polarization currents are being computed very accurately, the method is not capable of computing the extreme near zone electric fields of these currents with sufficient accuracy to compute the electric shielding factor. An alternate method, based upon the use of the volume equivalence theorem to directly compute the total electric field in the shield is devised, and is found to accurately compute the electric shielding factor     

New method for assessing EED susceptibility to electromagneticradiation

An infrared fiber optical temperature sensor (IFOTS) used for the measurement of induced electric currents caused by electromagnetic radiation in electroexplosive devices (EEDs) is presented. Features of the sensor include an infrared optical fiber that is immune to electromagnetic radiation, a probe assembly that eliminates any appreciable thermal and electrical loading of the EEDs bridgeware, a signal processing technique that enhances signals in the presence of noise, and a means of providing continuous and/or pulsed measurement of bridgeware temperature caused by induced electric currents     

Modeling of magnetic-field coupling with cable bundle harnesses

A field-to-line coupling model is developed for cable bundle harnesses in terms of the scattering currents and total line voltages. The equivalent distributed sources representing the effects of electromagnetic coupling are expressed as a function of the incident magnetic-field components. Such a formulation is particularly suitable to be used for the analysis of multiconductor transmission lines excited by a transient field, when data for the incident electric field are either inaccurate or not available. This model allows the accurate calculation of the induced voltages and currents on complex cable bundles. The effects on the induced voltages and currents due to ground losses and to the presence of the dielectric sheath in shielded and unshielded cables is discussed, considering bundles excited by either slow or fast transient fields. Numerical applications demonstrate the validity of the proposed procedure.     

Currents Induced in a Human Being for Plane-Wave Exposure Conditions 0-50 MHz and for RF Sealers

The currents induced in a human being were measured for plane-wave exposure conditions 0-50 MHz. These are used to point out that very large SAR's may be set up in the wet tissues for the cross section of the ankle for standing human beings exposed to electric fields suggested in the ANSI C95.1-1982 RF safety guide. For these exposure conditions, foot currents on the order of 627 mA are projected for a human adult of height 1.75 m for the frequency band 3-30 MHz with the value increasing to 780 mA for 40 MHz. The corresponding ankle-section SAR's are 182 and 243 W/kg. Using electromagnetic scaling concepts, SAR's as high as 371 and 534 W/kg are projected for ten- and five-year old children, respectively, for f = 50.7 and 62.5 MHz, E = 61.4 V/m (1 mW/cm2) recommended by the ANSI C95.1-1982 RF safety guide. The paper also gives currents induced by two sealer models and three industrial RF sealers for a human being under grounded and insulated conditions. Though smaller than those for plane-wave irradiation conditions, these currents may be substantial for high leakage fields that are quite typical.     

地基ELF线天线在地-电离层壳体中产生的场

为了研究地震产生的机理, 需要分析和研究地基极低频(Extreme-Low Frequency, ELF)电磁波的传播特性.地基任意ELF线天线产生的电磁场可由ELF点源产生的电磁场进行叠加.通过地基ELF点源电磁场的表达式导出了ELF线天线在地-电离层壳体中电磁场的表达式.利用加速收敛算法得到了单条和两条ELF线天线产生电磁场的场强空间分布图, 用色标表示场强值在空间分布的强弱.电场水平分量的场强值要比垂直分量的场强值小, 磁场水平分量的场强值要比垂直分量的场强值大.而且两条线天线产生的场强值要比单条线天线产生的场强值大.     

Noninvasive measurement of current in the human body forelectromagnetic dosimetry

Minimally perturbing, resistive, nonferrous probes were developed for noninvasively measuring hazardous currents induced in the human body by electromagnetic fields at 1-200 MHz. Each probe has a resistive toroidal coil that is placed around the leg or other body member. An electrostatic shield is required to limit capacitive coupling. A new shielded test fixture provides TEM fields for calibration with a voltage standing wave ratio (VSWR) less than 1.1 from 1 to 200 MHz. A man-sized phantom was exposed to the near field of a vertical monopole antenna at 29.9 MHz, and the value of the current measured in the leg with the probe is in reasonable agreement with measured heating. Analyses and experiments show that commercial ferrous current probes modify the circuit in which they are used, changing the current being measured. Less change is caused by the authors' nonferrous current probes     

Characterizing the Electric Field Coupling from IC Heatsink Structures to External Cables Using TEM Cell Measurements

One method for evaluating the unintentional radiated emissions from integrated circuits (ICs) involves mounting the IC on a printed circuit board (PCB) embedded in the wall of a transverse electromagnetic (TEM) cell. The signal voltages on the IC and its package produce electric fields that can couple to cables and other structures attached to the PCB, inducing common-mode currents that can be a primary source of unintentional radiated emissions. The signal currents in the IC and its package produce magnetic fields that can also result in common-mode currents on larger radiating structures. This paper describes a TEM cell measurement method employing a hybrid to separate the electric field coupling and the magnetic field coupling. The results of this measurement can be used to determine the product of the IC's self-capacitance and the effective voltage that drives this capacitance. This voltage-capacitance product characterizes the IC's ability to drive common-mode currents onto cables or enclosures due to electric field coupling. This information can then be used to estimate the resulting radiated emissions.     

Electromagnetic deposition in an anatomically based model of manfor leakage fields of a parallel-plate dielectric heater

An anatomically based 5628-cell model of a human being was used to calculate local, layer-averaged, and whole-body-averaged specific absorption rates and internal RF currents at 27.12 and 40.68 MHz for spatially variable electromagnetic fields of a parallel-plate applicator representative of RF dielectric heaters used in industry. The conditions of exposure of the man model considered are: isolated from ground, shoe-wearing condition, feet in contact with ground, and an additional grounded top plate 13.1 cm above the head to simulate screen rooms that are occasionally used for RF heaters. Since peak E fields as high as 1000-2700 V/m have been measured at locations typically occupied by the operator, significant internal RF currents on the order of 0.5-2.3 A are projected for the operators. Measurements of the foot currents at 27.12 and 40.68 MHz for a human subject are in reasonable agreement with the calculated values for the various conditions of exposure     

Electromagnetic fields: the jury's still out. 2. Societalreverberations

The debate over setting standards for exposure to power-frequency electromagnetic fields when science has not yet determined what levels, if any, are dangerous is examined. Regulatory agencies, standards bodies and utilities are struggling to make policy in the face of two opposing views: one camp believes the evidence of health effects is enough to warrant precautionary action to limit exposure, while the other insists that research must present proof of a harmful effect before practical limits (i.e. limits that can be achieved at a reasonable cost to society) can be determined. Burgeoning litigation over high-voltage transmission lines is making the task of providing power increasingly difficult for the utilities. Almost all utilities provide field measurements to customers upon request, and many have programs for characterizing magnetic fields in various environments. The IEEE's standards activity, which is the focus of voluntary efforts to establish EM (electromagnetic) fields standards in the United States is discussed, as well as national electric and magnetic field exposure standards for ELF (extremely low frequency) fields that have already been adopted by some countries. Some solutions for transmission lines, and the technological and economic factors entailed, are explored. The debate over the risk of electrical appliances is examined     

光纤传输表面电流探头的设计与校准

本文介绍了一种在强电磁场环境中用于检测表面电流强度的光纤传输表面电流探头。采用光纤代替传统的电缆传输,对强电磁场有很好的抗干扰作用,同时也大大减少了对周围空间场的扰乱。其核心的信号处理环节采用直接强度调制式光纤通信,即采用射频晶体管做前级放大,将电压信号转换为电流信号,对光电器件进行直接光强调制。该系统动态范同大,非线性失真小,带宽达到5～120MHz,最大可测试电流为4A。文中给出了光纤传输表面电流探头的校准测试实例以及传输阻抗曲线。     

Electromagnetic field exposure system for the study of possibleanti-cancer activity

The characteristics of a static and extremely low frequency (ELF) magnetic fields (H-field) exposure system are analyzed. The system has been successfully used in a series of animal experiments devoted to the study of a new potential application of electromagnetism in cancer therapy. The characterization of this exposure system contributes to the improvement needed in the understanding of the role played by the various exposure parameters such as field intensity and field components (static, ELF, or a combination thereof) in the induction of the observed anti-tumor efficacy. This knowledge is important for extrapolating exposure conditions from animals to humans. The exposure system provides static and ELF H-field with an intensity in the kA/m range. The system allows six animals to be treated simultaneously with almost the same total (static + ELF) H-field intensity, but with different static and ELF components and, consequently, with different induced electric field levels and currents. The H-field uniformity experienced by each mouse is 12.4%     

Primary VLF/ELF currents produced by heating the lower ionospherein parts of China

A new iterative method is employed to calculate the primary ELF/VLF currents produced by heating the lower ionosphere with powerful modulated waves. The calculations are mainly for parts of China, as well as For Tromso, Norway for comparison. The results indicate that first, there are many similar characteristics for Beijing and Tromso, secondly the ELF/VLF currents in Haikou are much larger than those in Beijing and Tromso if the natural electric fields are equal     

A survey of electric and magnetic fields among VDT operators inoffices

The ambient electric and magnetic fields as well as the electromagnetic fields associated with video display terminals (VDTs) at 150 offices are measured. The aim of the study is to determine the general level of the various electromagnetic parameters in offices and establish a technical base for a case referent study of skin symptoms among VDT workers. The median value of the 50-Hz background field in the 150 offices is 0.07 μT. Seven of the offices have background levels higher than 0.5 μT, which is high enough to cause distortion of the picture on the screen. The dominant source for electric fields in the ELF range is electric equipment in the office, not the VDTs. The equivalent surface potential is less than 0.5 kV for 63% of the measured VDTs. The computer monitor is a major source of magnetic fields in the offices. The median value of the magnetic field in the ELF range in front of the VDT is 0.21 μT, and in the VLF range it is 0.03 μT