T-matrix formulation of electromagnetic wave scattering by charged non-spherical scatterers

Abstract

In this paper, a method is proposed to solve the scattering of electromagnetic waves (EMWs) by a uniformly charged non-spherical scatterer. Based on Waterman's extended boundary method, a transition matrix between coefficient of the scattering field and incident field of a charged non-spherical scatterer is derived, called Tc-matrix. By using Tc-matrix, the scattering fields of charged non-spherical scatterers can be numerically solved. In the case of a charged rotationally symmetric non-spherical scatterer, the analytic mathematical expression of Tc-matrix is obtained, thus the analytical expression of scattering field is obtained. And the extinction characteristics of charged non-spherical scatterers, making use of charged spheroids as examples, are investigated. It is found that absorption is still the dominant mechanism of attenuation when electromagnetic waves travels through small charged spheroidal particles suspended in atmosphere, though the net surface charges can enhance the extinction/scattering/absorption of particle. The enhancement factors of extinction/absorption increases with increasing surface charge density and are much higher than the enhancement factor of scattering. It is shown that the equivalent sphere assumption, which was used in theoretical models of optical or scattering properties of charged or uncharged atmospheric or interstellar particles, could result in large errors, e.g., even over 100% for charged prolate spheroids, in theoretical prediction of absorption/extinction. Moreover, this inaccuracy due to the sphere assumption worsens for spheroids with either low or high aspect ratios h (i.e., prolate spheroid with h << 1, or oblate spheroids with h >> 1).