The near field of dipole antennas, part II: Experimental results

The results of an experimental program to evaluate the electric field near dipole antennas are presented. The measured field intensities are compared with the numerical values computed using the theory developed in Part I of this paper. The theoretical and measured field intensities are in excellent correlation even for observation points spaced from the axis of the dipole less than one hundredth of a wavelength. For thin dipoles (radius ≃ .002λ) the experimental measure of the E-field at the antenna surface or at one antenna radius distance has not been possible because of the practical limitation of available instruments. The experimental and theoretical results show that the field intensities near some parts of a dipole antenna are higher than predicted by commonly used formulas.     

Slot antenna in a resistive screen

The loss resistance and efficiency are calculated for a slot in a resistive screen and for the complementary dipole. Double numerical integration of the magnetic near field is used. The strip dipole loss resistance is three to five times that of the complementary slot for short elements     

电偶极子在无限大各向异性媒质中的辐射场

分析电偶极子在无限大各向异性媒质中的辐射场，得出了近区场地级数表达式。分析计算了电偶极子平行天于地磁场时在无限大均匀各向异性电离层中的远区场。     

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.     

On the magnetic dipole representation of small loop antenna

The use of a magnetic dipole to represent a small loop antenna is examined by comparing their field components. Particular attention is paid to the dipole approximation in the near field, and curves are presented which allow an accurate and rapid assessment to be made of the error as a function of angle and distance from the loop. The curves, which apply to any loop with a circumference between 0.0001 λ and 0.1 λ, enable the correction to the dipole field to be estimated. The difference between the loop and magnetic dipole fields is expressed algebraically for large distances from the loop, and for near-axial angles.     

Transponder Antennas in and Near a Three-Layered Body

The electric field in a three-layered half-space iluminated by an incident plane wave is reviewed and numerical data provided when the layers are skin, fat and muscle. The impedance and voltage across the load of a dipole antenna is discussed when this is located in each of the three Iayer and in the air near the surface. Bare and insulated antennas are considered over a frequency range up to 3 GHz with layer thicknesses of skin from 0.2 to 1.0 cm, and of fat from 0 to 1.5 cm. The transmitting problem is discussed as well as application of the results to finite bodies.     

Application of the TLM method to half-space and remote-sensingproblems

The problem of scattering and radiation in the presence of a material half-space is solved using the transmission line matrix (TLM) method. The TLM method is a general numerical method for obtaining an approximate solution to the time-dependent form of Maxwell's equations in the presence of complex environments. The method requires the discretization of the entire spatial domain of the problem and provides the transient response as well as (through discrete Fourier transform) the frequency domain response. The three-dimensional symmetric-condensed TLM node is applied. A total/scattered field formulation is applied to excite the space. The source used is an electrically short electric dipole and is described analytically in the time-domain. The method is used to calculate near field distributions (in both the time and frequency domain) and the change in source input impedance of a dipole radiator in the presence of a half-space. Numerical simulations relevant to the detection of buried objects are provided     

Prediction of radiation losses and emission from a bent wire by a network model

This paper presents the modelling of the radiation characteristics of bent wires calculated through various approaches. The total radiation loss from a bent wire and the distributions of these losses are calculated analytically, leading to a rapid estimation of the maximum E field in the far field via directivity estimates. Also, an expanded Hertzian dipole approach based on the Cartesian frame is formulated, which facilitates the calculation of the E field in both the near field and the far field, and determines the radiation patterns from the bent interconnect by a simplified numerical process. Detailed radiation patterns from bent wires with various bend angles are presented in three-dimensional (3-D) parametric views and two-dimensional (2-D) polar views. The radiation characteristics are analyzed and compared to the simulations from Expert MiniNEC. Good agreement is observed.     

电小线圈近场分析

天线的近场分析在近场通信(NFC)、电磁兼容(EMC)、阵列天线设计等领域越来越受到关注。准确高效的近场分析方法对于近场的分布控制和引导机制等有着重要的作用。本文针对典型天线磁偶极子(电小线圈)的近场进行了初步的理论研究,主要分析了磁偶极子的近场平均能量密度分布、有功功率和无功功率的关系和分布。并通过磁偶极子的场分量计算平均坡印廷矢量,从而定性分析了线圈"储能"和"辐射能量"的关系,同时根据平均坡印廷矢量给出了电小线圈的近场"储能"中能量流动的物理图像。本文还计算了磁偶极子的平均电场能量密度和平均磁场能量密度,并进一步分析了二者的分布以及比较了二者的大小关系。     

二项式光场中运动的([Ⅰ])型三能级原子偶极振幅平方压缩

采用求解Schr(o)dinger方程和数值计算方法,研究了与二项式光场相互作用的([Ⅰ])型运动三能级原子的偶极振幅平方压缩特性,分析了光场参数、场模速度参数、参数η和光场与原子的耦合系数对原子偶极振幅平方压缩的影响.结果表明,随光场参数增大,原子偶极振幅平方从无压缩到呈现周期性压缩,压缩深度逐渐加深;随场模速度参数增大,原子偶极振幅平方由周期性不完全压缩到完全压缩;随参数η增大,原子偶极振幅平方从不压缩到周期性压缩,最后过渡到不压缩;光场与原子的耦合系数不影响原子偶极振幅平方压缩.     

Uniform asymptotic formulas for the creeping wave field on or off acylinder

This work develops a uniform asymptotic formula for the creeping wave field in the shadow region of a conducting circular cylinder, excited by a magnetic line source or line dipole on the surface. Unlike previous developments in terms of Fock integrals, the uniform formula does not require switching between on and off surface formulas. Furthermore, the uniform formula is more accurate in the transition region near the surface, where neither the on nor off surface formulas work very well. Validation is by comparison with an exact numerical solution for the field due to a single surface ray. An empirical switchover criterion for the nonuniform formulas is suggested, and limitations of both the nonuniform and uniform formulas are discussed     

Energy absorption mechanism by biological bodies in the near fieldof dipole antennas above 300 MHz

The energy absorption mechanism in the close near field of dipole antennas is studied by numerical simulations. All computations are performed and validated applying the three-dimensional multiple multipole software package. The numerical model of the plane phantom is additionally checked by accurate as possible experimental measurements. For the plane phantom, the interaction mechanism can be described well by H-field induced surface currents. The spatial peak specific absorption rate can be approximated within 3 dB by a formula given here based on the incident H-field or antenna current and on the conductivity and permittivity of the tissue. These findings can be generalized to heterogeneous tissues and larger biological bodies of arbitrary shape for frequencies above 300 MHz. The specific absorption rate is mainly proportional to the square of the incident H-field, which implies that in the close near field, the spatial peak specific absorption rate is related to the antenna current and not to the input power     

An electric dipole and a spherical protrusion on a half-space

The 3D problem on the field of an electric dipole situated near a spherical surface partly projecting from a conducting half-space is considered. An analytical solution is obtained in the quasi-static approximation for rational angular points. The near field of the source is studied for various heights of the spherical protrusion.     

Complex-Point Dipole Formulation of Probe-Corrected Cylindrical and Spherical Near-Field Scanning of Electromagnetic Fields

A probe-corrected electromagnetic theory based on complex-point dipoles is presented for computing the field of an arbitrary source of finite extent (for example a test antenna) from measurements of its near field on a cylindrical or spherical scanning surface. By representing the probe with complex-point dipoles, probe correction is achieved by simple factors that involve Hankel functions evaluated at complex points. Only four complex-point dipoles are needed to represent a typical precision probe used in near-field measurements. The theory uses neither translation and rotation theorems nor differential operators. One disadvantage of the theory is that it employs nonlinear optimization to determine the parameters of the probe model. The complex-point dipole representation of the probe makes realistic simulations of near-field scanning systems straightforward. The cylindrical theory is validated through a numerical example. The spherical theory is validated by experimental data.     

纠缠原子与光场作用体系的压缩特性

研究了Kerr介质中初始处于纠缠态的两二能级原子与相干光场相互作用体系的压缩特性.通过数值计算,讨论了原子偶极间相互作用耦合常数和Kerr介质与单模腔场相互作用的耦合强度对体系中的双原子偶极压缩和光场压缩的影响.结果发现在弱光场情况下,纠缠态原子偶极间相互作用和Kerr介质与光场作用越强,都使原子偶极振幅压缩现象从压缩状态退缩到无压缩状态;在强光场情况下,纠缠态原子偶极间相互作用越强,光场振幅压缩次数增多、振荡频率变慢;Kerr介质与光场作用越强,光场振幅压缩次数减少、振荡频率变快.     

Effects of leaky-wave propagation in metamaterial grounded slabs excited by a dipole source

In this paper, dispersive propagation and radiation properties of leaky waves on metamaterial grounded slabs are investigated. The proper or improper nature of leaky modes supported by such structures is shown to be related to the metamaterial being /spl epsi/-negative, /spl mu/-negative, or double-negative, and to field polarization, giving rise to backward or forward radiation depending on the frequency range of operation. These spectral features and the associated frequency scan of the radiated beam are illustrated by considering the field excited by a dipole source in the presence of an infinite metamaterial grounded slab. The possibility to achieve nearly equal values for the phase constants of a TE and a TM leaky mode on a large frequency range is shown; this allows us to obtain a conical radiation pattern and, also, for suitable values of the attenuation constants, the radiation of a pencil beam at broadside. Conditions for achieving maximum power density at broadside are derived, when one constitutive parameter is much smaller than the other. In order to illustrate these novel features, numerical results based on experimentally tested dispersion models for permittivity and permeability of the metamaterial media are provided, concerning leaky-wave modal properties and near and far fields excited by a dipole source.     

Electromagnetic Excitation of PEC Slotted Cones by Elementary Radial Dipoles—A Semi-Inversion Analysis

A novel method is presented that is based on the use of the Kontorovich–Lebedev integral transform and the semi-inversion technique, developed for building the efficient and accurate numerical solutions to the boundary-value problems of electromagnetic wave scattering by the 3D coaxial slotted cones. A generic structure under consideration consists of two semi-infinite coaxial circular perfectly electrical conducting and zero-thickness cones with periodic longitudinal slots excited by a radial dipole. The considered problem is reduced to an infinite set of linear algebraic equations of the Fredholm second kind that is truncated and solved numerically. A detail analysis of the accuracy and convergence of the method is presented. The basic electromagnetic characteristics such as the field behavior near the structure singularities, field patterns in the wave zone, and field polarization for various problem parameters are investigated for the cones excited by on-axis elementary dipoles. The slotted cones allow obtaining more directional patterns in wider band than the solid ones.      

高Q Kerr介质腔内强相干光场与A型三能级原子相互作用中原子的偶极压缩效应

研究了处于高Q Kerr介质腔中强相干光场与A型三能级原子相互作用中原子的偶极压缩。着重讨论了Kerr介质、原子与光场间的耦合系数以及失谐量对原子偶极压缩的影响。     

高Q Kerr介质腔内强相干光场与∧型三能级原子相互作用中原子的偶极压缩效应

研究了处于高Q Kerr介质腔中强相干光场与∧型三能级原子相互作用中原子的偶极压缩．着重讨论了Kerr介质、原子与光场间的耦合系数以及失谐量对原子偶极压缩的影响。     

垂直于地磁场的电偶极子在电离层中的辐射场

分析了电偶极子垂直于地磁场时在无限大均匀各向异性电离层中的辐射场，得到了近区场的一般表达式及远区场的近似式。给出了远区场特别是考虑碰撞情况下的计算结果。