Electromagnetic Absorption in a Multilayered Model of Man

A multilayered planar model is used to examine the dependence of whole-body power absorption on the configuration of surface layers, e.g., skin, fat, and muscle which normally occur in biological bodies. It is found that the layering resonance for three-dimensional bodies (as opposed to the geometrical resonance) can be predicted quite accurately by a planar model. Calculations for a multilayered prolate spheroidal model of man predict a whole-body layering resonance at 1.8 GHz with a power absorption 34 percent greater than that predicted by a homogeneous model.     

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.     

Determination of Power Absorption in Man Exposed to High Frequency Electromagnetic Fields by Thermographic Measurements on Scale Models

When the body of man, small compared to a wavelength, is exposed to high frequency (HF) electromagnetic (EM) fields, the absorbed power density patterns and total absorbed power may be approximated by the simple superposition of the internal electric fields obtained from the quasistatic coupling characteristics of the electric and magnetic field components determined independently. These characteristics were obtained for full scale man by thermographic studies of power absorption in scale models of man exposed to fields at frequencies scaled up inversely proportional to the model size. A VHF resonant cavity was used to provide the necessary field strengths for producing measurable power absorption patterns under simulated HF exposure conditions. The results indicate that peak power absorption densities as high as 5.63 W/kg can be produced in man exposed to 10 mW/cm2 31 MHz radiation fields. The results show that the absorption decreases as the square of the frequency as predicted by theory for frequencies below 31 MHz.     

Electromagnetic Fields and Power Deposition in Body-of-Revolution Models of Man

Internal electromagnetic (EM) fields and power absorption in a homogeneous Iossy dielectric body of revolution are evaluated using the surface integral equation method. The method yields moment method solutions for the induced current densities on the body surface. The interior fields to the body are then evafuated via the reciprocity theorem and the measurement matrix concept. The bulk body power deposition is obtained by the integration of the surface Poynting vector. The method applies for a wide range of dielectric parameters (with epsilon/sub r/ from 1.1 to 10/sup 2/ and sigma from 0 to 10/sup 3/ mhos/m) in the resonance region. Numerical results for EM fields and power deposition in a body-of-revolution model of a human torso with height of 1.78 m are evaluated for frequencies of 30, 80, and 300 MHz. It is found that the strongest power deposition in the torso model occurs for fields polarized along the longest dimension and for frequencies near the first resonance (i.e., 80 MHz) of the torso body. Hot spots are also observed in the neck region of the torso body.     

Long-Wavelength Electromagnetic Power Absorption in Ellipsoidal Model of Man and Animals

A previously developed long-wavelength analysis is applied to ellipsoidal models of humans and experimental animals to obtain the distribution of tissue power absorption and average power absorption for different frequencies and orientations of the model with respect to the field vectors. Curves showing the distribution of absorbed power inside the model, and the average absorbed power versus frequency are presented for several species. Comparisons of calculated data with preliminary experimental data on monkeys are given. The theoretical results show that the power absorption in the ellipsoidal model is a strong function of frequency and orientation with respect to the incident plane wave field vectors. The quantitative data presented here are valuable for estimating tissue electromagnetic (EM) power absorption in experimental animals and humans. These data may also be used in extrapolating EM induced effects measured in animals to those expected in humans.     

Absorption Characteristics of Multilayered Sphere Models Exposed to UHF/Microwave Radiation

The interaction of electromagnetic plane waves with multilayered spherical models composed of lossy dielectric media that represent different biological tissues found in human and animal heads is examined in the frequency range 0.1 to 10 GHz. The model ranges in size from 2 to 12.5 cms outer radius and consists of a core of brain-like material surrounded by five outer layers of CSF, bone, fat and skin-dura tissues. The absorption properties of the model have been analyzed throughout this range of size and frequency. The distribution of internally deposited energy has also been investigated in detail for three basic spheres of 3.3, 6 and 10 cms radii, with emphasis on the creation of localized regions of strong heating (hot-spots). Based on these results, some generalized conclusions are presented on the interaction of microwaves with different sized biological objects.     

An Empirical Relationship for Electromagnetic Energy Absorption in Man for Near-Field Exposure Conditions

An empircal relationship is presented for the whole-body-average electromagnetic energy absorption in a 180-cell block model of man for near-field exposure conditions. Consideration is restricted to near fields with P polarization (no component of E directed arm-to-arm) in which the magnitude of the incident electric field is maximum immediately in front of the abdominal region. A highlight of this work is the considerably reduced whole-body average energy absorption for near-field partial-body exposures as compared to that obtained under plane-wave irradiation conditions.     

Electromagnetic Power Deposition in Prolate Spheroid Models of Man and Animals at Resonance

The Extended Boundary Condition Method is used to calculate resonance region power deposition in prolate spheroid models of animals and man. The mathematical models consist of homogeneous distributions of muscle tissue, although in the case of the man model calculations, a model consisting of homogenized muscle, fat, and bone is also considered. Calculations are made for bodies isolated in free space and irradiated by a plane wave. Resonant frequencies and power absorption characteristics are predicted for man and a number of commonly used experimental animals. The results given here will be useful in providing a theoretical basis for the interpretation of experimental results and in extrapolating experimentally derived animal results to man's body configuration.     

Specific Absorption Rates of Energy in Man Models Exposed to Cellular UHF Mobile-Antenna Fields

Thermography, nonperturbing temperature probes, and E-field sensitive diodes were used to quantify the SAR patterns in human models exposed to UHF mobile-antenna fields. The exposure conditions include man, woman, and child models in the standing position close to roof- and trunk-mounted antenna; man sitting in the back seat near a trunk-mounted antenna; child kneeling in the back seat and looking through the rear window. Incident power densities near the antennas were also measured. Based on the current ANSI radio-frequency protection guide, the exemption of 7-W input power will violate the ANSI primary exposure criterion, but satisfies the 8-W/kg exclusion clauses. A maximum power of 3.5 W would satisfy all of the ANSI guides.     

Analysis of Electromagnetic Scattering from an Eccentric Multilayered Sphere

An exact analytic solution of a plane electromagnetic (EM) wave scattered by an eccentric multilayered sphere (EMS) is obtained. It is assumed that the layers are perfect dielectrics and that the innermost core is a perfectly conducting sphere. Each center of a layer is translated along the incident axis. All fields are expanded in terms of the spherical vector wave functions with unknown expansion coefficients. The addition theorem for spherical wave functions is used prior to applying the boundary conditions. The unknown coefficients are determined by solving a system of linear equations derived from the boundary conditions. Numerical results of the scattering cross sections are presented on the plane of φ=0 degrees and φ=90 degrees. The convergence of modal solutions and the characteristics of patterns are examined with various geometries and permittivity distributions     

Interaction of Electromagnetic Waves with Cylindrical Plasma

Exact numerical solutions are given for the interaction of a plane, electromagnetic wave with a cylindrical plasma. The incident wave is normal to the plasma axis and both TE and TM polarizations are considered. The electron density profile is represented by a Gaussian curve consistent with flow-field calculations for wakes and jets. Transmitted and scattered amplitudes are evaluated as functions of the polar angle and plasma parameters. The data are compared with previous theoretical and experimental work. [17],[18] Parabolic electron density profiles are also investigated and contrasted with the Gaussian results. The sharp cutoff in a parabolic profile has a significant effect on the electromagnetic interaction. Applications to microwave diagnostics are discussed including a new bistatic method.     

电磁波多层媒质传播的[C]网络新理论

本文讨论电磁波在多层媒质中传播的反射和折射。将电磁波斜入射到媒质突变的平面边界作为基本模型,推广到垂直入射和导体、磁体边界等多种情况。本文将电磁波传播和网络理论有机结合,创新地提出多层媒质的[C]网络理论,从而把困难的多层媒质传播转化为[C]矩阵级联,概念简单,结果统一。文中还给出了具体实例。     

Electromagnetic Field Penetration into a Cylindrical Cavity

For an E-polarized plane wave incident on a perfectly conducting cylindrical shell having a longitudinal slit aperture, the fields inside the cavity are determined by a numerical solution of the E-field integral equation. Selected data are presented and the first few complex frequency (SEM) singularities are determined for a variety of aperture sizes.     

多层各向异性等离子体球电磁散射的解析解

给出s层各向异性等离子体球电磁场球矢量波函数解析表达式,应用电磁场在(s-1)层球壳边界上切向电磁场连续以及辐射条件,导出了平面波入射情况下,s层等离子体球电磁场的展开系数。将数值计算结果分别与矩量法-共扼梯度-傅里叶变换(MOM-CG-FFT)计算结果和均匀等离子体球的结果进行了比较,符合得较好。该文研究结果预期可应用于新型天线的研制和卫星通信等领域。     

圆柱螺旋线的时域电磁场

给出一个单连通的空间电流线圈在远区辐射的的时域电磁场，应用等效性原理和场的迭加性，求出圆柱螺旋天线的辐射场分析。     

Frequency-Dependent Absorption of Electromagnetic Energy in Biological Tissue

The frequency-dependent absorption of electromagnetic energy in biological tissue is illustrated by use of the Debye equations, model calculations for different irradiation conditions, and measured electrical properties (conductivity and permittivity) of different tissues. Four separate irradiation conditions are treated for calculating the power absorbed. in a given tissue when it forms a flat interface or is surrounded by another tissue. The calculations show that the greatest differential absorption occurs at frequencies between the dominant relaxation frequencies in the two tissues. From rat mammary gland tumor data, the calculations show an optimum frequency range of about 100-500 MHz for microwave hyperthermia treatment of at least these types of tumor.     

Scatteration and Absorption Characteristics of Multilayered Gratings Embedded in a Dielectric Slab*

A rigorous and simple method of analyzing scattering and absorbing characteristics of multilayered gratings embedded in a dielectric slab has been proposed. The method combines a generalized scattering matrix with a lattice sums matrix and a T-matrix of an isolated single cylinder instead of the aggregate T-matrix. The validity of the present method has been confirmed by several numerical experiments and comparisons with other published results. Numerical examples show that the absorbing characteristics become very complex and are not linear with the decreasing of cylinders’ conductivity, when the arrays are stacked to a multilayered structure and are embedded in a dielectric slab.     

非同轴多层介质椭圆柱体的电磁散射—任意方向斜入射电磁波

本文基于椭圆柱谐基函数展开，对非同轴任意多层介质椭圆柱体的电磁散射进行了严格地电磁场分析，利用Ｍａｔｈｉｅｕ函数及其加法定理，在各层边界面上进行场的匹配，获得了任意方面斜入射电磁波下电磁散射解析解。     

垂直入射时无限长多层介质圆柱的内,外场计算

本文提出了一种稳定而准确的迭代算法，计算任意多层吸收介质圆柱电磁散射的散射系数ａｎⅡ和ｂｎⅠ及各层内场系数ｃｎ＾（ｊ），ｄｎ＾（ｊ），ｇｎ＾（ｊ），ｆｎ＾（ｊ），给出了它们适合于计算机数值计算的形式和数值结果，该算法对于各种复介电常数和复磁导率以及电尺寸参数均适用。