Melina P. Ioannidou

Induced EM field in a layered eccentric spheres model of the head: plane-wave and localized source exposure

The induced electromagnetic (EM) field in a layered eccentric spheres structure is determined through a concise analytical formulation based on indirect mode-matching (IMM). The exact analytical solution is applied to a six-layer model of the head. This model allows for eccentricity between the inner and outer sets of concentric spherical layers which simulate brain and skull, respectively. Excitation is provided by a nearby localized source or by an incident plane wave. The numerical application provides information about the total absorbed power, the absorption in each layer, and the spatial distribution of the specific absorption rate (SAR) at frequencies used by cellular phones. The effects of excitation frequency, eccentricity, exposure configuration, and antenna-head separation are investigated.

Radio-wave exposure of the human head: analytical study based on a versatile eccentric spheres model including a brain core and a pair of eyeballs

A versatile eccentric-spheres model of the human head is used to investigate radio-wave absorption. Numerical results, obtained by use of an exact analytical solution, are presented for the total, percentage, and gram-specific absorption. Interest is mainly in the brain and in the eyes of an adult or an infant head. Our model comprises a host sphere and several spherical inclusions, all concentrically stratified with respect to their own center. Any number of inclusions and any number of concentric layers for the host sphere and each one of the inclusions can be considered. Excitation is provided either by a plane-wave or by a nearby electric dipole. The analytical solution is obtained by use of the indirect-mode matching method. The theory of this paper and the accompanying computer code constitute a versatile tool for analytical studies of cellular-phone interactions with the human head. Specific absorption rate maps in a horizontal cross section of the head model manifest the existence of hot spots in the eyes and near the center of the brain.

Indirect mode-matching solution to scattering from a dielectric sphere with an eccentric inclusion

The analytical formulation of electromagnetic wave scattering from an eccentrically stratified dielectric sphere is greatly simplified through the indirect mode-matching technique. The resulting exact solution is the most compact available and hence the least prone to analytical or numerical errors. After some checks we present a comparison between our solution and two previous solutions that were obtained through direct mode matching. Our numerical investigation is focused on an acrylic sphere with an eccentric cavity. All four elements of the scattering matrix are available, and specific information about the possibility of detecting the scatterer’s internal asymmetry is given.

Study of interactive scattering by clusters of spheres

A compact extended Mie solution to electromagnetic scattering from a cluster of spheres is obtained through indirect mode matching. Our interest is focused on interactions among member spheres, as manifested in multiple scattering from the cluster. We therefore define and investigate the interactive-backscattering cross section of the cluster and the interaction length of member spheres. Numerical results are presented to probe the effect of sphere spacing as well as the effect of look direction and incident polarization on interactive backscattering from silicate clusters. Moreover, we present a brief extinction and absorption study of a soot particle near a cloud droplet.

Electromagnetic-wave scattering by a sphere with multiple spherical inclusions

An exact solution to the problem of electromagnetic-wave scattering from a sphere with an arbitrary number of nonoverlapping spherical inclusions is obtained by use of the indirect mode-matching technique. A set of linear equations for the wave amplitudes of the electric field intensity throughout the inhomogeneous sphere and in the surrounding empty space is determined. Numerical results are calculated by truncation and matrix inversion of that set of equations. Specific information about the truncation number pertaining to the multipole expansions of the electric field intensity is given. The theory and the accompanying computer code successfully reproduce the results of other pertinent papers. Some numerical results [Borghese et al., Appl. Opt. 33, 484 (1994)] were not reproduced well, and that discrepancy is discussed. Our numerical investigation is focused on an acrylic sphere with up to four spherical inclusions. This is the first time that numerical results are presented for a sphere with more than two spherical inclusions. Interesting remarks are made about the effect that the look direction and the structure of the inhomogeneity have on backscattering by the acrylic host sphere.

Electromagnetic-wave scattering by an eccentrically stratified, dielectric cylinder with multiple, eccentrically stratified, cylindrical, dielectric inclusions

A cylinder with an arbitrary number of cylindrical inclusions, all eccentrically stratified, parallel, and infinite in length, may serve as generic model of several bodies, natural or artificial. The electromagnetic field within such a complex cylindrical structure, as well as the scattered wave, is determined in this paper by use of the indirect mode-matching method. A linearly polarized, plane wave, normally incident upon the stratified cylinder, is used as excitation. The resulting analytical solution is exact in the sense that no approximation is used in any part of the analysis, except for the truncation of multipole expansions for the electric- field intensity. Application is made to a model of the human leg. Interest is in the effect of osteoporosis on the tangential field at the perimeter of the gastrocnemial. Appropriate values for the frequency, polarization, and angle of incidence of the excitation are determined and appropriate points on the perimeter of the leg are proposed for measurements of the aforesaid effect.

Analytical study of the changes in the color of daylight due to sulfate droplets and soot grains in the atmosphere

Absorption of daylight by an atmospheric layer that comprises non-interacting water and sulfate droplets, interstitial soot grains, and composite sulfate-soot particles is determined by use of exact theories of Mie or extended-Mie scattering from all types of suspended particles. Interest is in the color of the sky, as observed from the ground underneath a light-absorbing atmospheric layer which has been synthesized as above. The end-result of the theory presented in this paper is the spectral radiant power distribution and the colorimetric features of daylight at ground level. The numerical application manifests that microlensing by sulfate droplets gives rise to enhanced absorption by soot grains, which results in attenuation and redshifts of daylight. An investigation is made of the changes in the color of the sky, as observed from the ground, due to pollution of the air by sulfuric acid and carbon.

Light scattering and absorption by soot in the presence of sulfate aerosols.

The radiative properties of aerosol-soot mixtures, both internal and external, are determined in the visible and near-infrared bands by use of exact indirect mode-matching solutions to electromagnetic-wave scattering from a sphere with an eccentric spherical inclusion and from a cluster of spheres. Spherical sulfate droplets are assumed to represent aerosol particles. Soot particles are represented by volume-equivalent carbon spheres, the size distribution of which is obtained from the number distribution of the primary carbon particles that aggregate into soot grains. The mean gram-specific absorption cross section and the mean albedo of aerosol-soot mixtures are obtained by integration of the corresponding characteristics of composite sulfate-carbon particles over the size range of carbon spheres. Enhanced absorption of light by soot in aerosol-soot mixtures, a result of lensing by sulfate droplets, is highlighted by maps of the electromagnetic field in a sulfate-carbon particle.

Scattering of radiowaves by melting ice particles: an eccentric spheres model

Abstract Melting ice particles are modeled as ice spheres eccentrically coated by a spherical water shell. The existing exact solution to plane-wave scattering from a sphere with an eccentric spherical inclusion is used to determine scattering from individual melting ice particles. The size distribution thereof is determined from the size distribution of the resulting raindrops by use of the mass conservation principle. Scattering characteristics across the melting layer of precipitation are determined by integration of the corresponding characteristics of melting ice particles over their size range. The numerical results provide information about the reflectivity, attenuation, and phase shift across the melting layer of precipitation. Effects associated with the formation of a bright band are discussed and comparison with relevant published results is made. Maps of the internal and near field of a melting ice particle of average size are presented for every phase of the melting process.

Dual-Series Solution to EM-Wave Scattering by a Circular Slit PEC Cylinder Enclosing Multiple Dielectric Cylindrical Rods

A cylindrical structure composed of a circular, PEC cylinder, having a longitudinal slot and enclosing an arbitrary number of eccentric, dielectric cylinders, embedded in a dielectric sheath, is considered in this paper. Excitation is provided by a plane wave, normally incident upon the structure. Both TE and TM polarizations are considered for the incident wave. The scattered wave, as well as the electromagnetic (EM) field within the scatterer, are determined by using a dual-series approach combined with the translational addition theorem for cylindrical wave functions. The Abel integral-transform method is applied in order to regularize the dual-series equations to a matrix Fredholm equation of the second kind. The resulting infinite set of linear algebraic equations (i.s.l.a.e.) is truncated and solved numerically. The solution inherently contains the behavior of the field near the aperture rim, as required by Meixners edge condition. The numerical application manifests how the internal structure of the scatterer and the polarization of the incident wave affect backscattering by the cylindrical cavity.