Radially inhomogeneous spherical structures; analysis of EM scattering using Taylor’s series method and their potential applications

Spherical structures have always been among the most frequently studied topics by researchers in engineering electromagnetics. In this paper, electromagnetic (EM) scattering from radially inhomogeneous spherical structures is investigated in the most general cases. Unlike previous investigations, these structures are studied based on an exact frequency domain method without any approximations. Two main categories of applicable inhomogeneous spherical structures exist: inhomogeneous spheres and spherical arbitrary cores, coated with a radially inhomogeneous layer. One of the biggest advantages of this research investigation is the generality and inclusiveness in analyzing all of the aforementioned circumstances. The validity of the proposed method is verified for some special types of inhomogeneous structures through comprehensive examples. In the last section, the proposed method is used for designing of the optimized new class of lens based on the physical concept of gradient refractive index material, and radar cross section reduction based on gradual wave absorption. The proposed approach can be used for other interesting applications such as designing radar absorbers, cloaks and radomes for spherical structures in future researches.     

不均匀磁等离子体的隐身机理——圆极化电磁波的碰撞吸收

研究了圆极化电磁波在不均匀磁等离子体的传播和吸收。讨论了不均匀磁化等离子体片对平行于磁场方向传播的左、右旋圆极化电磁波的碰撞吸收，计算了不同条件下衰减率。计算表明，当电磁波的频率接近电子碰撞频率时，磁等离子体对电磁波的吸收达到最大值。当入射电磁波的频率很低时，不均匀磁化等离子体中磁撞对雷达波的吸收非常小。当入射电磁波频率较高时，等离子体的碰撞对入射电磁波的衰减很有效。     

1千伏以下的金属球间隙静电放电辐射特性的测量研究

In this study, the characteristics of Electromagnetic (EM) radiation caused by Electrostatic Discharges (ESDs) from metal spheres charged to voltages less than 1 kV are examined experimentally. Our experimental system consists of a pair of spherical elec-trodes of different diameters, a 1-18 GHz-band- width horn antenna and a 20-GHz-bandwidth digitizing oscilloscope. Polarization, waveform duration and peaks of antenna-received voltages from the EM field radiation are measured in order to clarify the EM radiation mechanism. The ratio of the received voltages between the antenna arr-angements of the field polarization parallel and perpendicular to the spark pass is 18 to 20 dB. The polarities of the antenna-received voltages are the same as those of the charge voltages across the gap. Moreover, the waveform duration and the first peaks increase with an increase in the diameters of the spherical electrodes. Consequently, we find that the polarization, waveform duration and first peaks of the EM field radiation can be explained by a dipole antenna structure, which makes the spark part of the spherical electrodes a feeding point on the straight line passing through the centres of the two spheres.     

FDTD Simulation of Electromagnetic Reflection of Conductive Plane Covered with Imhomogeneous Time-Varying Plasma

A finite-difference time-domain (FDTD) algorithm is applied to study the electromagnetic reflection of conduction plane covered with inhomogeneous, collision, warm, time-varying plasma. The collision frequency of plasma is a function of electron density and plasma temperature. Under the one-dimensional case, transient electromagnetic propagation through various plasmas have been obtained, and the reflection coefficient of EM wave through inhomogeneous time-varying plasma (ITVP), homogeneous time-varying plasma (HTVP) and inhomogeneous plasma (IP) are calculated under different conditions. The results illustrate that a plasma cloaking system can successfully absorb the incident EM wave.     

Antenna Modeling Based on a Multiple Spherical Wave Expansion Method: Application to an Antenna Array

A method to derive an equivalent radiation source for planar antennas is presented. This method is based on spherical near-field (NF) data (measured or computed) to ascertain an equivalent set of infinitesimal dipoles placed over the main antenna aperture. These produce the same antenna radiation field, both inside and outside the minimum sphere enclosing the antenna. A spherical wave expansion (SWE) of the NF data is written in terms of infinitesimal dipoles using a transition matrix. This matrix expresses the linear relations between the transmission coefficients of the antenna and the transmission coefficients of each dipole. The antenna a priori information are used to set the spatial distribution of the equivalent dipoles. The translational and rotational addition theorems are exploited to derive the transmission coefficients of the dipoles. Once the excitation of each dipole is known, the field at any aspect angle and distance from the antenna is rapidly calculated. Computations with EM simulation data of an antenna array illustrate the reliability of the method.      

NUMERICAL SIMULATION OF ANNULAR PHASED ARRAY OF DIPOLE ANTENNAS USING THE FD-TD METHOD

The problem for calculating near fields of EM radiation systems by using the finitedifference time domain(FD-TD)method are discussed and the annular phased array of dipoleantennas has been simulated numerically by use of the FD-TD method.For a test run thenear field and current distribution of the single dipole antenna are calculated.The near fieldsof the annular phased array of dipole antennas in central region filled with deionized water arecomputed and the interaction of near fields with an anatomically-based inhomogeneous model ofhuman torso is considered as well.     

Electromagnetic scattering by an inhomogeneous plasma anisotropic sphere of multilayers

Electromagnetic scattering by an inhomogeneous plasma anisotropic sphere is formulated and obtained, where the inhomogeneous plasma anisotropic sphere is divided into (s-1) homogeneous anisotropic spherical layers. The electromagnetic fields in the inner spherical multilayers and outer free space of the inhomogeneous plasma anisotropic spherical structure can be expanded in terms of the spherical vector wave functions in plasma anisotropic medium and in isotropic medium, respectively. By applying the continuous boundary conditions of electromagnetic fields on the spherical interfaces of the (s-1)-layered homogeneous anisotropic plasma medium, the unknown expansion coefficients of fields in the multilayered plasma spherical structure are obtained, and then the electromagnetic field distributions are calculated. Numerical results for the very general inhomogeneous plasma dielectric material sphere are given and the data in a special case are obtained using the present method and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach and compared to each other to verify the correctness and applicability of the present analysis.     

Construction of solutions to electromagnetic problems in terms of two collinear vector potentials

In this paper, the construction of solutions to transient electromagnetic (EM) problems in terms of two collinear vector potentials (VPs) is subjected to a careful theoretical study and numerical verification. The analysis concerns a general isotropic medium that can be inhomogeneous, lossy, and may contain sources. It is also assumed that the medium has instantaneous response, i.e., its EM properties are frequency independent. First, the completeness of the solution in terms of the two VPs in homogeneous and inhomogeneous media is addressed. Second, the behavior of the VPs at interfaces and edges is considered. Finally, a number of simple, but relevant numerical tests are performed to verify the theoretical model. This paper is part of the effort to establish the theoretical background of a novel efficient approach to the analysis of transient EM propagation based on the VPs.     

Three-dimensional electromagnetic power deposition in tumors usinginterstitial antenna arrays

Interstitial arrays of insulated antennas have shown promise for microwave hyperthermia treatment of deep-seated tumors. Available analytical techniques for predicting the electromagnetic (EM) power deposition of these antennas have been limited to the case of a homogeneous conductive medium surrounding the array. Since tumors and host tissue may differ in their electrical characteristics, it is necessary to consider the impact of this variation in electrical properties and the geometry of the tumor in the calculation of the EM field distribution and power deposition pattern when modeling interstitial antennas. In this paper a three-dimensional model of a tumor of arbitrary shape subjected to the fields of an interstitial antenna array is developed to predict the EM power deposition in an inhomogeneous tumor-tissue medium. The volume integral equation for the imbedded tumor is developed and solved by method of moments. The incident fields are calculated based on the available formulation of interstitial antennas in homogeneous media. The accuracy of the developed computer code was checked by comparing the results from the volume integral approach with the Mie solution for the special case of spherical tumors. Good comparison was obtained for tumors with properties approximately 25 percent different from those of the surrounding tissue. Comparisons of results from models of antenna arrays with and without imbedded tumors show significant differences in their predictions of the EM power deposition in the tumor. Hyperthermia protocols generally specify uniform temperature distribution within the tumor. The developed inhomogeneous model was used to examine the feasibility of controlling the uniformity of the power deposition pattern in large tumors by adjusting the amplitude or relative phase between the array elements. Results are presented to show that a phase lead of +90 degrees or relative amplitude of 4.0 on one antenna in a square array of four antennas could be used to shift the power deposition pattern to sequentially heat outer portions of a 2 cm diameter tumor, thereby achieving a more uniform time-averaged temperature distribution in the tumor.     

Adaptive restoration of textured images with mixed spectra

We consider the adaptive restoration of inhomogeneous textured images, where the individual regions are modeled using a Wold-like decomposition. A generalized Wiener filter is developed to accommodate mixed spectra, and unsupervised restoration is achieved by using the expectation-maximization (EM) algorithm to estimate the degradation parameters. This algorithm yields superior results when compared with supervised Wiener filtering using autoregressive (AR) image models.     

Finite Element Method for Inhomogeneous Axisymmetric Resonators

A finite element method(FEM) with hybrid nodal and edge basis functio ns for solving nonaxisymmetric modes in axisymmetric resonators filled with in homogeneous media is presented. Spurious modes can be reduced by choosing proper basis functions. Several numerical results are presented to show the validity a nd the efficiency of proposed method.This method can be widely used in electroma gnetic(EM) engineering design.     

THE RELATIONSHIP BETWEEN THE EM ENERGY ABSORPTION OF HUMAN BODY AND THE INCIDENT DIRECTION AND POLARIZATION OF PLANE WAVE

The problems of EM energy absorption of human body irradiated by plane wave arediscussed by the Finite-Difference Time-Domain(FD-TD)method.The local Specific AbsorptionRates(SARs),the whole-body average SARs and the layer average SARs for the inhomogeneousblock model of human body with different incident direction and different polarization of theincident waves are calculated.The results show that the appearance of maximum EM energyabsorption is not always at the situation of the front incidence and the local SARs are moreimportant for the interaction of the EM fields with human body.All results provide more infor-mation about the electromagnetic dosimetry for human body.     

含片状粒子涂层的热辐射

用几何光学绕射理论研究了片状粒子的散射，由非均匀系统的热辐射传输方程求出了含片状粒子涂层的表观比辐射率，讨论了片状粒子的线度、体积化、涂层厚度等因素对涂层系统辐射性能的影响，比较了含片状粒子涂层和含球状粒子涂层的辐射性能。     

脉冲电磁波对人体作用的研究

用时域有限差分法和非均匀块状人体电磁模型研究了脉冲电磁场对人体的作用问题，首先用解析法计算无限长介质圆中脉冲波所引发的电流以验证计算方法，然后对核电磁脉冲照射下的二维和三维非均匀块状人体模型中产生的电流及所吸收的电磁能量进行了，计算了它们随时间的变化及其在全身的分布，在计算中没有考虑介质色散的影响。     

显示器电磁泄漏信息的接收和重现

计算机电磁泄漏信息的接收和重现对信息侦收和安全传输都具有重要意义。显示器上的信息是有用信息的最直接体现 ,而且很容易通过电磁辐射产生泄漏。通过无线接收显示器的电磁辐射信息并经过数据采集卡输入到计算机 ,实现了原始信息的还原处理。该系统适用面广 ,方便灵活 ,运行结果证明该方法是切实可行的。     

Liquid crystal microlens arrays with switchable positive and negative focal lengths

A flat microlens array whose focal length can be switched from positive to negative by electric field is demonstrated experimentally and confirmed by computer simulations. To generate the required gradient refractive index, an inhomogeneous electric field is created by a spherical indium-tin-oxide (ITO) electrode which is imbedded in the top flat substrate. The bottom substrate has a planar ITO electrode on its inner surface. A thin polymeric layer is overcoated on top of the spherical ITO to create a flat surface. The disclination lines are eliminated. Because of the employed dual-frequency liquid crystal, the microlens array has fast response times.     

Exact solutions of electromagnetic fields in both near and farzones radiated by thin circular-loop antennas: a general representation

This paper presents an alternative vector analysis of the electromagnetic (EM) fields radiated from thin circular-loop antennas of arbitrary radius a. This method, which employs the dyadic Green's function in the derivation of the EM radiated fields, makes the analysis more general, compact, and straightforward than those two methods published recently by Werner (1996) and Overfelt (1996). Both near and far zones are considered so that the EM radiated fields are expressed in terms of the vector-wave eigenfunctions. Not only the exact solution of the EM fields in the near and far zones outside the region (where r>a) is derived by the use of the spherical Hankel function of the first kind, but also the closed-series form of the EM fields radiated in the near zone inside the region 0⩽r   

FEM/BEM混合法计算各向异性不均匀介质柱电磁散射

应用有限元-边界元(FEM/BEM)混合法计算二维各向异性不均匀介质柱电磁散射,对介质柱内、外区域分别采用有限元和边界元法进行分析,然后应用边界条件建立部分稀疏部分满填充的矩阵方程.应用内观法结合多波前法求解该矩阵方程,分别计算了均匀分布和不均匀分布的各向异性介质柱的雷达散射截面.数值计算表明,有限元-边界元混合法在分析和计算不均匀开放域电磁问题时有一定的优势.     

Reliable prediction of EM radiation from a PCB at the design stageof electronic equipment

This paper presents a composite computer-aided design (CCAD) package for prediction of electromagnetic (EM) radiation from a printed circuit board (PCB) at the design stage of equipment. Such a CCAD package has been developed by combining an EM computation tool such as numerical electromagnetic code (NEC)-2, with other circuit design packages (CDPs). The method of prediction of EM radiation using the CCAD is well described in this paper. The predicted EM radiation has been validated experimentally and results showing good agreement are presented. Finally, the reliability of the CCAD package is investigated and presented     

Long-Wavelength Electromagnetic Power Absorption in Prolate Spheroidal Models of Man and Animals

A previously developed electromagnetic (EM) field perturbation analysis is used to calculate the electric fields in tissue prolate spheroids irradiated by plane waves with long wavelength compared to the spheroid dimensions. This theory is applied to prolate spheroid models of man and animals to obtain internal electric field strength, absorbed power distribution, and total absorbed power. These data are of value in estimating tissue EM power absorption in experimental animals and man. The theory may be used to help extrapolate animal biological effects data to man, and as a guide to establishing an EM radiation safety standard.