Power Deposition in a Spherical Model of Man Exposed to I-20-MHz Electromagnetic Fields

The induced fields and the associated power deposition in mail exposed to HF electromagnetic (EM) fields have been investigated theoretically using spherical models. The induced electric fields inside the model exposed to either plane wave or near fields can be described adequately by a combination of quasi-static electric and magnetic induction solutions. It is shown that for field impedances less than 1200/spl pi//spl Omega/ the magnetically induced energy absorption predominates. Therefore, H fields must be measured to obtain any estimate of the hazards due to HF exposure. For a 70-kg model of man exposed to a plane wave field, the theory indicates that the time-average power absorption per unit volume is less than 2.5x10/sup -3/ mW/g for each milliwatt per square centimeter incident at 20 MHz and below. This suggests that the thermal safe-exposure levels for the HF band are many orders of magnitude in excess of the 10-mW/cm/sup 2/ level recommended for the microwave region.     

Exact solution for the characteristic impedance of rectangularcoaxial cone transmission line

The exact and approximate expressions for the characteristic impedance of a rectangular coaxial cone transmission line are obtained using the conformal mapping method. The formula is exact and simple, so, it enables the characteristic impedance of a broadband transverse electromagnetic (TEM) cell to be calculated accurately and easily. This broadband TEM wave cell, has increasing applications in both electromagnetic interference and electromagnetic compatibility measurements     

加载横电磁传输室中的电场分布计算

用“准静脉法”研究了当工作频率远低于截止频率时,放置于横电磁传输室中的被测物体中的电场分布。文中使用的是有限差分法,给出了在三维空间中不同介质交界面上拉普拉斯方程的差分格式。计算结果表明当把ＥＴＵ放入ＴＥＭＣｅｌｌ的中心时,ＥＵＴ横截面上的电场分布是均匀的。     

Minimization of backscattering of a loop by impedance loading--Theory and experiment

A study on the minimization of the backscattering of a conducting loop by the impedance loading method is presented. A conducting circular loop loaded symmetrically with two identical lumped impedances is assumed to be illuminated by a plane electromagnetic wave at normal incidence. The induced current on and the backscattered field by the loaded loop are determined. The optimum impedance loading for zero backscattering is obtained. The optimum reactive loading for minimum backscattering is also studied. An experiment was conducted to verify the theory.     

A Rigorous Solution for Dispersive Microstrip

Closed-form solutions are presented for the frequency-dependent characteristic impedance of microstrip as defined by the ratio of the electromagnetic power to the square of the electric current. The analysis uses the rigorous spectral-domain approach based on the charge-current formulation. Analytical expressions for the impedance solutions show that the frequency dispersion occurring in microstrip is characterized in terms of three different impedances. The characteristic impedance of a TEM line given in the limit as the frequency decreases is derived from one of these impedances, and the other two are involved in expressing the nature of dispersion to vanish in the limit. Conversely, as the frequency increases, these dispersive parts grow rapidly. Some comments are given in conjunction with previous works.     

Calibration cell for E-field sensors in water environment

Compact and nonperturbing E-field sensors are used for antenna near field measurements. For application in the research area of hyperthermia these sensors are used in a water environment. Owing to the high dielectric constant of water in the frequency range from DC to ~1 GHz the sensitivity is changed. To perform a calibration of E-field sensors, a water-filled TEM-cell has been developed. The technique employs a transverse electromagnetic (TEM) transmission cell that operates as a 50 W impedance matched system. A uniform TEM-field is established inside the cell     

A General Multisegment Artificial Neural Network Architecture for the Efficient Evaluation of Electromagnetic Plane-Wave Wedge Diffraction

A multisegment artificial neural network (ANN) is proposed as an interpolation technique for the evaluation of the electromagnetic field diffracted at the edge of anisotropic impedance wedges under plane wave illumination at oblique incidence. Multisegmentation is needed as the high-frequency wedge diffracted field is characterized by a number of discontinuities at the shadow boundaries of the geometrical optics and surface wave fields. The proposed approach is applied, as a test case, to the problem of an anisotropic impedance right-angled wedge illuminated by a skewly incident plane wave. Some exact analytical solutions valid for specific surface impedance tensors are used to obtain numerical data for the ANN training phase as well as to show the interpolation capabilities of the implemented ANN. Nevertheless, the proposed ANN structure is general and can be trained with data obtained from other available solutions (analytical, perturbative, numerical) valid for more general wedge configurations, eventually leading to a single software tool encompassing all of them and providing accurate approximations of the wedge diffracted field in a relatively short time, comparable to that of a closed form analytical solution.     

Uniform diffraction coefficients for an impedance wedge

Uniform diffraction coefficients for an astigmatic electromagnetic wave normally incident on a wedge having curved faces with given surface impedances are derived from the earlier work of Maliuzhinets. These coefficients are to be used with standard formulas in the geometrical theory of diffraction to predict diffraction effects from structures having impedance surfaces terminating in an edge.     

Antenna Link Transfer Function Factorization Applied to Optimized Channel Design

A channel broadband factored model is developed and numerically verified with a method of moment (MoM) technique for design of optimized UWB links with real, dispersive antennas. In this study, two-antenna link transfer functions are decomposed into port-load and full-wave dependent components based on general linearity and reciprocity in electromagnetics. Specifically, the port-related components account for antenna termination to the transmitter generator and front-end receiver circuits as antenna loads. In turn, the wave portion, which is associated with link transmission impedance, involves all geometrical factors like antenna shapes and their positioning/pointing in space that account collectively for radiation, propagation and reception. As a result, any link of fixed geometry can be full-wave numerically simulated just once for a suitable set of reference generator/load impedances. Then, all variations in link performance caused by variable port terminations are easily predicted by manipulating the full-wave data obtained for the case of reference antenna port loads. This approach provides some useful physical insights and an optimized co-design procedure for transmitter and receiver impedances to meet several significant performance-related design objectives, such as: i) maximized link energy transmission efficiency; ii) maximum amplitude of received signals; iii) minimized time confinement for signal energy at receiver loads; iv) flatness of magnitude of link transfer functions; and v) minimized group delay deviation. The major results are numerically illustrated for a number of useful far-field line-of-sight link cases with flat and solid dipole antennas operating in up to 3:1 bands and ideally aligned in terms of their gain and polarization matching. Numerical results are given in a normalized form and scalable to any band of interest.     

Generalized Theory of Impedance Loaded Multiconductor Transmission Lines in an Incident Field

A general theory is advanced for determining the currents in the load impedances of an N-conductor isolated transmission line excited by an electromagnetic field with the electric vector directed parallel to the wires. The number of impedance loads in the circuit is 2N. An impedance is connected in series with each conductor at its ends. At each end of the transmission line the impedances emanate from a common node. There is no requirement that the conductors be of the same radius, be equally spaced, or lie in a common plane; however, their axes must be parallel. Evidently the cross section of the line must be sufficiently small in terms of the wavelength that transmission line theory applies. Numerical values for the load currents In a three-conductor model are given. Scattering from end loaded multiconductor transmission lines is considered. It is shown that for configurations lacking geometrical symmetry such problems become arduous if not solved by computer.     

An efficient method for the performance analysis of bounded-wavenuclear EMP simulators

The author discusses an approach for analyzing the electromagnetic performance of bounded-wave nuclear electromagnetic pulse (NEMP) simulators. This method is extremely efficient and enables even the largest simulators to be analyzed. Typical bounded-wave EMP simulators are composed of flat-plate transmission-line sections approximated by wires. Using a priori knowledge as much as possible, the method presented obtains the current in the wave launcher's wires from an approximation of the current in a conical-plate wave launcher that generates a spherical TEM wave propagating along the radial direction. This method uses TEM-like currents obtained by approximating the TEM-mode current in the conical-plate wave launcher. The transient electromagnetic fields within the simulator's working volume are then readily computed by using efficient and analytical time-domain expressions for the fields generated by the wires. Expressions for the early-time fields and the impedance of a conical wire-mesh wave launcher are derived. Numerical results are presented for EMPSIS, a triangular-plate simulator for ships     

过孔转换信号完整性分析的区域分解有限元法

提出了一种基于区域分解的二维有限元法分析多层印制电路板电源/地平面中过孔转换结构的信号完整性.过孔电流产生的电磁场呈三维结构,其中,一部分电磁波沿过孔轴向传输,另一部分电磁波在电源/地平面间沿径向传播.采用一虚拟柱面将求解区域分割为过孔区和电源/地平面区.将过孔区建模为以周向磁场为主分量的二维轴对称问题,而将电源/地平面区建为以垂直电场为主分量的二维模型.首先求解电源/地平面区的二维边值问题获得分割边界上节点的波阻抗,然后将该波阻抗代入过孔区模型中分割边界节点的边界条件,从而计算出过孔信号传输的S参数.所提方法通过模型缩减可实现对微细过孔结构信号完整性的精确快速计算,且采用全波电磁场分析软件对算法的有效性和准确性进行了验证.     

Metaparticles of Pulsed Wave Fields

Properties of elementary particles of pulsed (localized) electromagnetic and acoustic wave fields directionally radiated by aperture sources (antennas, lasers, acoustic diaphragms) in free space and homogeneous isotropic media, for which the term metaparticle is used, are considered. The structure of the wave field and the energy transferred by the metaparticles are presented. The results obtained for the presented scalar theory of metaparticles of pulsed transverse electromagnetic (TEM) waves and longitudinal elastic acoustic waves can be extended to vector pulsed wave modes guided by layered inhomogeneous guiding media and guiding technical devices (waveguides).     

Analytical-Numerical Calculation of Diffraction Coefficients for a Circular Impedance Cone

An analytical-numerical computation of diffraction coefficients is described for a semi-infinite impedance cone of circular cross section illuminated by an electromagnetic plane wave. To enable an incomplete separation of variables, both the incident and scattered fields are expressed in terms of the Kontorovich-Lebedev (KL) integrals; an inversion of the Leontovich condition on the cone's surface yields equations for the spectra, whose Fourier coefficients satisfy certain functional difference equations of the second order; the latter are then converted to integral equations of the second kind which are solved numerically; using the so obtained spectra in the KL-integrals for the scattered field and evaluating the integrals in far field leads to diffraction coefficients. Numerical results are included both for verification purposes and for displaying the diffraction behavior for different incident and diffraction angles, as well as for several cone impedances.     

Finite-difference time-domain analysis of a complete transverseelectromagnetic cell loaded with liquid biological media in culturedishes

Transverse electromagnetic (TEM) cells can be used for exposing biological culture specimens to electromagnetic fields and observing possible anomalous effects. The uniformity of field exposure is critical to quantifying the biological response versus the electromagnetic dose. Standing waves and other electromagnetic field nonuniformities can cause nonuniform exposure. This paper reports the results of high-resolution three-dimensional finite-difference time-domain (FDTD) simulations of a complete TEM cell designed for operation at 837 MHz. Several different cases were studied in which the number of culture dishes, the depth of the culture liquid, and the orientation of the culture dishes were varied. Further, the effect of the culture-dish glass bottom thickness and the meniscus of the liquid medium were examined. The FDTD results show that there is a significant nonuniform field and specific absorption rate (SAR) distribution within the culture medium for each case examined. Hence, biological dose-response experiments using the TEM cell should account for the possibility of strong localized SAR peaking in the culture media to provide useful data in setting exposure standards for wireless communications     

Wiener-Hopf analysis of the EM diffraction by an impedancediscontinuity in a planar surface and by an impedance half-plane

The Wiener-Hopf technique is used to solve two canonical problems. The first problem considered is the electromagnetic (EM) diffraction, by a planar surface with an impedance discontinuity (two-part surface), of an arbitrarily polarized plane wave obliquely incident to the axis of the two-dimensional objects. The second problem considers the EM diffraction by a half-plane with equal impedances on both sides. The solutions obtained are cast in a matrix notation which is useful for diffraction problems. The exact formal solutions are expressed in terms of integrals which can be asymptotically evaluated. Uniform asymptotic expressions are obtained where the presence of the geometrical optics (GO) poles as well as the surface-wave poles near the saddle point are fully taken into account. Several numerical examples are presented and it is shown that the solutions are continuous across the shadow boundaries of the GO and surface-wave fields     

Loaded TEM cell versus free space: comparison of the E-fieldsinside dielectric spherical objects

A Crawford (1974) cell is a convenient tool for generating transverse electromagnetic fields. In this work, a dielectric hemisphere is assumed to be placed on the central septum of a Crawford cell; the field inside the hemisphere is numerically evaluated and then compared with that inside the corresponding sphere in free-space (illuminated by a plane wave) for which the analytical solution is known     

Theoretical modeling of longitudinal variations of electric fieldand line impedance in TEM cells

Longitudinal variations of the electric field inside a TEM cell have been observed in an in-depth experimental investigation and reported by M.L. Crawford et al. (see IEEE Trans. Instrum. Meas., vol.26, pp.225-230, Sept. 1977). Here, the authors present a theoretical approach to modeling these variations using standard transmission-line techniques, since only the dominant mode, TEM mode, is considered in this analysis. In addition, longitudinal variations of line impedance in the TEM cell are modeled. Their relations with voltage standing wave ratio (VSWR), losses, cell dimensions, and terminal load impedance are reflected in the expressions derived. Numerical results agree well with the reported experimental data at some frequencies. Concepts concerning longitudinal nonuniformity of both the field and the line impedance are proposed     

Electromagnetic Fields in Complementary and Self-Complementary Structures

Electromagnetic fields are analyzed in complementary and self-complementary structures. As is well known, Maxwell's equations exhibit a complementary (duality) symmetry between the electric and magnetic fields. Self-complementary field solutions (when these exist) on self-complementary structures have particular properties of constant impedance (resistance) associated with certain pure traveling wave fields. The contribution of this paper is that it rigorously treats the electromagnetic field in a self-complementary waveguide. It shows a self-complementary field solution is a pure traveling wave. A particular waveguide structure is selected that illustrates circumstances when a self-complementary field solution fails to exist in a self-complementary structure. A computer model was developed to analyze a family of waveguide structures that differ only in an aspect ratio parameter, an aspect ratio of 1.0 corresponding to the self-complementary case. The original structures and the corresponding complementary structures are analyzed independently. Results are presented for a wide range of frequencies and aspect ratios. At low frequencies, when only one TEM mode propagates, field solutions for the input TEM mode exhibit discontinuous behavior as the aspect ratio approaches one from above and below. In this frequency range, no time harmonic self-complementary field solution exists for the precisely self-complementary waveguide structure.     

椭圆柱传输线内的TEM波及其特性阻抗

利用复数坐标系z上的儒可夫斯基变换,给出椭圆柱传输线内的TEM波的电磁场分布规律,利用数学软件Matlab绘制出TEM波在椭圆柱传输线横向截面上的场结构图,并计算出其特性阻抗。