ELF and VLF fields of a horizontal electric dipole

The waves in the spherical guide between the earth and ionosphere are excited by a horizontal electric dipole. The guide boundaries are characterized by surface impedances and the resulting waves are expressed as a superposition of TM and TE modes. The wavenumbers, excitation factors, height-gain functions, and height-dependent impedances are examined for both types of modes. A thin-shell approximation of the radial wave functions is shown to be adequate for phase velocity estimates; but other propagation parameters are of restricted validity in the VLF range where Airy integral approximations provide more reliable data. A horizontal electric dipole is shown to provide a nearly omnidirectional coverage of horizontal field components in the frequency range of the lower Schumann resonances. For an elevated source the horizontal fields are essentially omnidirectional also in the VLF range. Near fields are expressed as a summation of waveguide modes. The vertical field components vanish at the antipode, but the horizontal components remain of finite magnitude.     

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.     

Biological effects of electric and magnetic fields associated with ELF communications systems

The U.S. Navy has proposed a submarine communications system that operates at extremely low frequencies (ELF). The land-based transmitting antenna for this system consists of insulated conductors 50 to 100 km long, grounded at each end, and driven by a generator such that the flow of current would be along the cable, into the ground, deep in the earth, and return to the other grounded end of the cable. It would, in effect, be a large loop antenna in which the earth was part of the loop. Over the last ten years the Navy has sponsored a wide variety of research to evaluate the environmental impact of this system. A discussion of this work can logically fall into three periods: 1968 to 1973, 1973 to 1977, and work still in progress. The work during the first period was reviewed by an Ad Hoc Committee formed in 1973 by the Navy. A second committee was formed in 1976 by the National Academy of Sciences and charged to review all existing data. These committees have reported their findings but they are not readily available in the open literature. This paper does not duplicate the work of these committees but rather summarizes their results and combines them with more recent work some of which is still in progress.     

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.     

Steady-state and shock currents induced by ELF electric fields in ahuman body and a nearby vehicle

Steady-state currents induced in a human body and a nearby car by 60-Hz electric field of a high-voltage power line are determined, taking into account the coupling between the body and the car. The equivalent circuits for the body and the car are constructed on the basis of their calculated open-circuit voltages and short-circuit currents. A theoretical model and a method for predicting the shock current that may flow between the body and the car are developed using their equivalent circuits. The theory is verified by existing experimental results     

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     

Simple estimation of equivalent magnetic dipole moment tocharacterize ELF magnetic fields generated by electric appliancesincorporating harmonics

A simple method of quantifying the ELF (extremely low frequency) magnetic field distribution around electric appliances, which takes the harmonics into account, is newly proposed. The proposed method involves: (1) a simple estimation of the position of an equivalent magnetic dipole moment inside an appliance, using two magnetic field meters; (2) identification of the amplitude of the dipole moment magnetic-field measurements at certain points; and (3) calculation of the magnetic field distribution around the appliance using the estimated dipole moment. In this method, the dipole moment vector is assumed to be a similar value by allowing an uncertainty of 6 dB in the estimated magnetic field, which enables easy estimation of the dipole moment. In addition, the frequency characteristics of the magnetic field are taken into account by considering the harmonic components in the magnetic field waveform. The proposed method was applied to 13 types of appliances, and their equivalent magnetic dipole moments and harmonic components were determined. The results revealed that the proposed method is applicable to many electric appliances. The conditions required for the adoption of the method were also clarified     

Exposure of workers to intense RF electric fields that leak from plastic sealers

This paper presents the results of an environmental investigation in a plastic-ware industry using RF sealers. Environmental measurements have demonstrated the presence of strong electric fields the intensity of which: reaches significant levels from the health-protection point of view only in proximity to the applicators; often exceeds the maximal levels allowed by all standards (including the most permissive) for short duration exposures, especially in the region of the hands. Results of a cross-sectional study on the health of 63 female workers are related to the observed RF exposure. A statistically significant correlation was found to exist between RF exposure and some minor health effects--eye irritation, upper limb paresthesias, and vitreous body disorganization.     

Generalized representation of electric fields in interaction gaps of klystrons and traveling-wave tubes

Analytic expressions for axial and radial electric fields in axisymmetric interaction gaps of klystrons and coupled-cavity traveling-wave tubes are derived. Introduction of a field-shape parametermallows a continuous transition in gap-edge field distribution between the limit of a uniform constant field for relatively blunt tunnel tips to the limit of a field rising to infinity with infinitely sharp tunnel tips. With values ofm = 0andm = infincorresponding to these limits, intermediate values of m yield field distributions that very closely approximate the actual field distributions occurring in interaction gaps. A comparison is made between the analytically computed field distribution and the field distribution obtained by experimental measurement and by relaxation computation in a klystron cavity.     

RF power transistor storage time: theory and measurements

Measurements on two types of UHF power transistors are given. The measured charge storage time constants (/spl tau//SUB s/) were 89 ns and 173 ns, effectively `infinite' for most applications. Then t/SUB s/ is essentially independent of /spl tau//SUB s/, and depends mainly on circuit properties: base drive and collector current waveforms. The measured dependence of t/SUB s/ on circuit and transistor parameters is in accordance with analytical predictions. Therefore storage time can be accounted for explicitly in a priori circuit design of RF power amplifiers.     

Self-pulsating semiconductor lasers: theory and experiment

We report detailed measurements of the pump-current dependency of the self-pulsating frequency of semiconductor CD lasers. A distinct kink in this dependence is found and explained using a rate-equation model. The kink denotes a transition between a region where the self-pulsations are weakly sustained relaxation oscillations and a region where Q-switching takes place. Simulations show that spontaneous emission noise plays a crucial role in the cross-over     

激光场与两能级原子相互作用的全量子理论分析

本文用全量子理论研究激光场与两个原子的相互作用。在不同的初始条件下,得到了光子数和原子状态各自随时间的变化关系。光子数很大时,全量子理论结果与半经典理论结果是一致的。     

On the interaction between electric and magnetic currents in stratified media

The presence of both electric and magnetic current elements embedded in stratified media is necessary to model many problems of interest in current integrated circuit and printed antenna technology. The integral equation formulation as applied to these problems is reviewed. Special attention is given to the Green's dyadic for the electric field generated by a magnetic current element. The fact that spectral-domain transmission line Green's functions for a multilayered structure are closed form integrable along the axis normal to the stratification is exploited to greatly improve the efficiency and the accuracy of the method. Theory and implementation are demonstrated in two practical problems: 1) arbitrarily shaped apertures in thick conducting screens, and 2) a metallic airbridge over a slot line.     

Near-field gain of a horn and an open-ended waveguide: Comparison between theory and experiment

Generating a standard electromagnetic field requires knowledge of the gain of the transmitting antenna. The theory and supporting experimental measurements of the near-field gain of a pyramidal horn and an open-ended waveguide (OEG) at 450 MHz are given. The empirical near-field gain for the OEG is derived from experimental results obtained by a two-antenna method at about 2 GHz. The theoretical nearfield gain for the rectangular pyramidal horn is derived from Schelkunoff's formula. Two independent near-field gain measurements of these antennas are made using a three-antenna method and a transfer-standard-probe method. The discrepancy between theoretical and experimental results is typically less thanpm 1dB.     

A fast diffusion-driven photodetector: theory and experiment

A high-speed photodetector has been demonstrated. Prototype silicon devices have detection bandwidths of 5 GHz and are limited by neither the saturation-velocity transit time nor the carrier lifetime. These detectors use a combination of the Dember effect and the east of generating fine photocarrier gratings, and scale to bandwidths of several hundred gigahertz     

Optimized overlay metrology marks: theory and experiment

In this paper, we provide a detailed analysis of overlay metrology mark and find the mapping between various properties of mark patterns and the expected dynamic precision and fidelity of measurements. We formulate the optimality criteria and suggest an optimal overlay mark design in the sense of minimizing the Cramer-Rao lower bound on the estimation error. Based on the developed theoretical results, a new overlay mark family is proposed-the grating marks. A thorough testing performed on the new grating marks shows a strong correlation with the underlying theory and demonstrate the superior quality of the new design over the overlay patterns used today.     

Immunity tests of implantable cardiac pacemaker against CW and pulsed ELF fields: experimental and numerical results

The aim of the present work is to investigate pacemaker (PMK) immunity against high-level extremely low frequency (typically 50 Hz) magnetic fields that can be found in industrial environment where high power machines operate. To that purpose, a test bench has been set up using a Helmholtz coil for producing extremely low frequency magnetic fields and a trunk simulator rightly fed by cardiac signals. A widely used PMK was tested, and results have been reported, under different operating conditions, for both continuous waves and variously pulsed excitations. A numerical tool has also been developed to analyze the realized test bench, based on a proper discretization of a human trunk simulation and on the construction of an equivalent three-dimensional (3-D) network. Numerical results have showed a good agreement with the experimental results.     

Differential drain resistance of field-effect transistors beyond pinch-off: A comparison between theory and experiment

The theoretical computation of the drain characteristics of junction field-effect transistors reported by Kim and Yang has been compared with the experimental measurements in terms of the differential drain resistance. Good agreement between the theory and experiment has been found.