Radiation characteristics of a dielectric disk-loaded circularcylindrical waveguide

The radiation pattern of a circular cylindrical waveguide that is loaded inside with periodically spaced dielectric disks is derived by considering the region between two disks as a medium with anisotropic permittivity and using Schelkunoff's equivalence principle. The far-field electric field components and their relationship to cross-polarization ratio are determined. The variation of the latter quantity with the size, spacing, and dielectric constant of the dielectric disks is studied     

The surface impedance anomaly resulting from a subsurface,infinitely long conductive wire

The change in surface impedance caused by the fields generated by an infinitely long, subsurface wire located in a homogeneous lossy medium (e.g., the Earth) is investigated experimentally and numerically. Sets of curves illustrate the variation in the horizontal electric field, the horizontal magnetic field, and the surface impedance as a function of conductor depth. The half-width at half-amplitude (HWHA) can be used as a measure of the lateral dimensions of the anomaly. While the horizontal magnetic field HWHA is equal to the conductor depth, the horizontal electric field HWHA (and so the surface impedance HWHA) varies not only with depth but also with the conductivity of the medium     

Effect of surface boundary on neuronal magnetic stimulation

The effect of the surface boundary between free space and a conducting medium on the excitation properties of neurons by magnetic fields are analyzed. The electric field and the spatial derivative of the induced field generated by a coil mounted both parallel and perpendicular to the surface of a semi-infinite conducting medium were calculated using the method of images. An imaginary axon is located in the same relative position from the coil in both configurations and the excitation properties are compared. The calculations are expressed in terms of the activating function for the electrical stimulation of axons. The calculations indicate that the activating function for magnetic stimulation is biphasic as opposed to triphasic for electrical stimulation. The large spatial extent of the magnetically induced electric field compared to the electric field generated by point source electrode suggests a different mode of excitation for neuronal structures in the CNS. The field distribution have been verified experimentally and are important for the understanding of the mechanisms of magnetic stimulation of neural tissue.     

Near fields of a linear antenna

The near fields of a strip antenna in free space have been computed by modifying a variational-impedance formulation. Current distributions, which vary linearly with distance near the ends of the antenna, excite strong tangential electric fields on the antenna surface. Such surface fields are avoided by choosing the axial antenna current to vary in proportion to the square root of the distance from the antenna ends. This modification of the antenna current is not necessary, however, for field calculations at distances comparable to the antenna width. The fields parallel to the antenna surface decrease with increasing distance from the antenna near the driving point and the antenna ends, but are found to increase in an intermediate range.     

一种背栅极冷阴极器件中纳米线表面电场的分析

利用静电场理论计算了背栅极冷阴极器件的纳米线附近电场,给出电场分布的表示式及J-V曲线,并分析了几何参数对纳米线顶端表面电场的影响.结果表明,纳米线顶端表面产生巨大的电场,随着离纳米线顶端表面距离的增大,电场迅速下降;纳米线突出栅孔的长度(L-d1)越大,纳米线半径r0、栅孔半径R以及栅极与阳极间距d2越小,则纳米线顶端表面电场越强,而d2较大时d2对表面电场的影响很弱;纳米线顶端边缘电流密度J随着阳极与栅极电压的增加而指数增大.     

Electromagnetic scattering from a chiral cylinder of arbitrarycross section

A simple moment solution is presented to the problem of electromagnetic scattering from a homogeneous chiral cylinder of arbitrary cross-section. The cylinder is assumed to be illuminated by either a TE or a TM wave. The surface equivalence principle is used to replace the cylinder by equivalent and magnetic-surface currents. These currents radiating in unbounded external medium produce the correct scattered field outside. When radiating in an unbounded chiral medium, they produce the correct total internal field. By enforcing the continuity of the tangential components of the total electric field on the surface of the cylinder, a set of coupled integral equations is obtained for the equivalent surface currents. Unlike a regular dielectric, the chiral scatterer produces both copolarized and cross-polarized scattered fields. Hence, both the electric and magnetic current each have a longitudinal and a circumferential component. These four components of the currents are obtained by using the method of moments (MoM) to solve the coupled set of integral equations. Pulses are used as expansion functions and point matching is used. The Green's dyads are used to develop explicit expressions for the electric field produced by two-dimensional surface currents radiating in an unbounded chiral medium. Some of the advantages and limitations of the method are discussed. The computed results include the internal field and the bistatic and monostatic echo widths. The results for a circular cylinder are in very good agreement with the exact eigenfunction solution     

Characteristics of near field of the horizontal vibrator located above a square screen

The 3D vector problem concerned with the diffraction of the horizontal half-wave vibrator field by a perfectly conducting and infinitely thin rectangular screen is solved during observations at a finite distance from the vibrator. The technique for calculating the diffracted field, which is based on the laws of geometric diffraction theory and uniform diffraction coefficients obtained from the rigorous solution to the problem of the diffraction of the field of a Hertzian electric dipole at the edge of a perfectly conducting semiplane, is proposed. Fast-acting programs for calculating and analyzing the amplitudes and phases of the components of diffracted and complete vibrator fields in the entire space of observation angles at the set distance of the observation point from a rectangular screen and along the normal to the screen under changes in the distance between the screen and the observation point are developed. The character of the transformation of the spatial amplitude distribution of three field components depending on removal of observation point from an antenna is studied. It is shown that the distance to the far field zone of the investigated radiating system exceeds two wave lengths.     

Control of electric field at the surface of P-N junctions

Both degradation resulting from ion migration and surface breakdown ofp-njunctions depend strongly on electric field. These problems can be minimized or avoided by designingp-njunction devices so that the electric field at the surface is substantially lower than that within the body of the device. The shape, surface doping, and dielectric constant at the junction-surface interface have an appreciable influence on the electric field of the adjoining space charge layer. Using relaxation methods, solutions of Poisson's equation in two dimensions have been found which permit predictions of the surface fields as a function of surface geometry and dielectric coatings. Measurements of the surface field by probing the junctions are in good agreement with calculated values. This approach has led to the design of very high voltagep-njunction devices which exhibit body breakdown only. With the breakdown confined to the body of the device, the reverse power dissipation capability is not only predictable but significantly greater (typically 30 a at 1200 v for a 100 µsec pulse applied to a large area device) than that achievable with surface limited devices.     

前栅极冷阴极器件中单根纳米线表面电场分布研究

利用静电场理论,对带栅极纳米线场发射冷阴极器件模型进行电场计算,在此基础上,进一步对器件几何参数以及电压对纳米线顶端表面电场的影响做了理论分析。结果表明,在纳米线低于栅极的情况下,纳米线顶端表面电场强度比其他点更强,随着离纳米线顶端距离的增加,电场急剧下降;栅孔半径、阴极与栅极距离的减小以及纳米线长度的增加,均使纳米线顶端表面电场大大增强,而栅极与阳极间距变化对顶端表面电场的作用很微弱;另外,纳米线顶端表面电场随栅极和阳极电压的增加而大幅度增强,尤其栅极电压的变化对纳米线顶端表面电场的影响更大。     

对称结构光子晶体表面Tamm态的光学性质

利用传输矩阵理论和等效原理,从能级的角度研究对称结构光子晶体表面Tamm态的光学性质,结果表明:在有限排列周期结构光子晶体中,介质表面可支持表面Tamm态的存在,且轴向传播时通带中出现TM和TE偏振的能级简并现象,离轴传播时从通带边缘分离出来的非简并能级被局域于光子晶体表面而形成了光学Tamm态；表面Tamm态内存在很强的局域电场,而且局域电场在介质界面处分布最强；表面Tamm态内的能量输运,对于低折射率介质可正反两方向输运,且输运速度快,对于高折射率介质只能正向输运,且输运速度较慢,故在高折射率介质界面处形成很强的局域光场。对称结构光子晶体表面Tamm态光学性质可为光子晶体光波导和表面波传感器的研究和设计提供指导。     

Electromagnetic Fields at the Top of a Tall Building Associated With Nearby Lightning Return Strokes

We have calculated, using the finite-difference time-domain (FDTD) method for solving Maxwell's equations, the vertical electric field E_z and azimuthal magnetic field H_phi due to lightning return strokes in the presence and in the absence of a building at the field point. Strikes to both flat ground and tall objects of height h = 100, 200, or 500 m are considered. The magnitude of H_phi is not much influenced by the presence of either building at the field point or strike object, while the magnitude of E_z is significantly influenced by either of them. In the case of a lightning strike to flat ground, the magnitude of E_z at the top of the building (at the center point of its flat roof) of plan area S_b = 40 times 40 m² and height h_b = 20, 50, or 100 m located at horizontal distance ranging from 100 to 500 m from the lightning channel is about 1.5, 2, or 3 times, respectively, greater than that at the same horizontal distance on the ground surface in the absence of the building. The enhancement factor for lightning (transient) E_z due to the presence of the building at the field point is essentially not influenced by the presence of the strike object (up to 500 m in height) and is similar to the static electric field enhancement factor due to the presence of the same building in a uniform vertical electric field. The magnitude of the electric field at the corner of the building is about two to three times larger than that at the center point of its flat roof. The magnitude of E_z at the ground level in the immediate vicinity of the building is reduced relative to the case of no building, with this shielding effect becoming negligible at horizontal distances from the building exceeding twice the height of the building.     

Near-field measurements of VLSI devices

This short paper describes a technique for the measurement of the electric near field at the package surface of microprocessors and other VLSI devices. The technique uses precision stepper motors for highly accurate placement of an electric field probe at the surface of the device to be measured. Structural resolution across the device is on the order of 400-600 μm. Typical scans accumulate 10000 data points across a variable scan area, which can be defined by device package dimensions or by the die dimensions. Characterizing a device involves a repeated series of surface scans at harmonics of the fundamental clock frequency. This paper describes the electric near field at the surface of a multichip module (MCM) composed of a processor, a flash memory, and application specific integrated circuit (ASIC). The MCM was measured while in operation in the actual circuit application     

Power Flowing through the Surface of a Large-Current Radiator

A previously developed theory permitted us to calculate the electric and magnetic field strength produced by a current with arbitrary time variation flowing in a large-current radiator for any distance from the surface of the radiator to infinity. This permits one to determine Poynting's vector on the surface of the radiator and, by integrating it over the surface, to calculate the power flowing through the surface of the radiator at any time. One obtains the power radiated to the far zone, the power contained in the various near-zone components, and the required driving voltage. The influence of the antenna dimensions on these quantities may be studied to help with the design of better antennas.     

A Comprehensive Study of Subsurface Propagation from Horizontal Electric Dipoles

The general exact integrals for the electromagnetic field of an electric dipole in the earth near its boundary with the air are evaluated numerically over the full range of conductivities and permittivities that characterize different parts of the earth's surface. The following ranges are included: permittivities from 2 to 80, conductivities from 4 × 10-6 to 4 S/m, frequencies from 10 to 109 Hz, radial distances from 0.1 to 100 km, and depths of the source and point of observation from 0.15 to 15 m. The generally useful component of the electric field E? is represented in graphs and contour diagrams that display the characteristics of propagation in their dependence on the frequency, the radial distance, the depth, and the electrical parameters of the earth. They are interpreted in terms of approximate formulas of Ba?os which are evidences of the lateral-wave nature of the field.     

Critical distance for grating lobe series

Estimating a transition or critical distance above a planar periodic array of point sources radiating into an unbounded medium is considered. It is shown that as an observation point approaches a periodic planar phased array of point sources, the corresponding spectral-domain Green's function, or grating lobe series, converges much more slowly than an equivalent mixed-domain representation exhibiting Gaussian convergence. For a given argument of the Green's function, the critical transition distance above the array for which both representations take the same time to compute can be estimated numerically. Since phased array antenna structures with cavity- or waveguide-type backings often have dimensions that fall well below the critical distance, investigations of such structures would seem to benefit significantly from formulations incorporating such hybrid Green's functions     

Rayonnement d’une antenne microruban de forme arbitraire

This paper gives a rigorous approach to the problem of the radiation of microstrip antennas by using the surface electric currents circulating on the upper conductor of the antenna (patch). The model used in this study is a stratified medium in which the substrate and the ground plane both have infinite transverse dimensions. Asymptotical expressions for the far field of a Hertz dipole, located on the surface of the substrate, are obtained with a complex integration technique in the spectral plane. The radiated fields result from the superposition of a spherical space wave and a cylindrical surface wave. The relative amplitude of both waves and their behaviour in terms of substrate parameters and frequency are discussed in some detail. Finally, the theory of antenna arrays was utilized to evaluate the radiation of a microstrip antenna of arbitrary shape.     

The Response of a Terminated Two-Wire Line Suspended in Air Above a Semi-Infinite Dissipative Medium and Excited by a Plane-Wave RF Field Generated in Free Space

The analysis previously made to determine the response of a two-wire transmission line buried at constant depth near the earth-air interface when excited by a plane-wave electromagnetic field generated in free space is extended to include the case of the line suspended in air at a uniform distance above the earth's surface. The exciting field is the vector sum of the incident and reflected fields at the point midway between the line conductors. The polarization of the electric field is taken to be parallel to the wires, so that there is no pick up by the terminations. The objective of the study is to determine bounds for the current in specified load impedances in terms of the amplitude of the incident electric field evaluated at the surface of the earth.     

Radiation from harmonic sources in a uniformly moving medium

In this paper the Maxwell-Minkowski equations are used to find a general integral for the electromagnetic fields in an infinite moving medium. The medium is assumed to be homogeneous, isotropic, and to move with a constant velocity much less than the speed of light. Only time-harmonic fields are considered. A wave equation for the electric field is derived and is integrated by means of a Green's Identity and an appropriately defined Dyadic Green's Function. The result gives the electric field inside a volume of space in terms of known sources in the volume and the tangential components of the electric and magnetic fields over the enclosing surface. Finally, the fields radiated by a point dipole are found.     

LEMP 空间表达式求解及分布规律研究

利用偶极子理论对Maxwell方程组进行了求解,得到了垂直通道与斜向通道模型的雷电电磁场解析表达式。基于此表达式分析了不同高度处雷电电磁场的空间分布规律。研究结果表明,在垂直通道与斜向通道模型中,垂直电场和磁场受观测点高度的影响随水平距离的增加而减小,但是对水平电场而言,在垂直通道模型中其初始峰值随着观测点高度增加而增加,在斜向通道模型中,当观测点在通道下方时电场峰值随着观测点高度的增加而增加,当观测点在通道上方时高度越高电场峰值越小。