Open AccessThe influence of magnetic properties on the absorption of porous spheres
Author(s) -
Coulson S. G.
Publication year - 2008
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2008.13717.x
Subject(s) - refractive index , dielectric , absorption (acoustics) , permittivity , porosity , physics , spheres , absorption spectroscopy , spectral line , porous medium , optics , mixing (physics) , condensed matter physics , molecular physics , analytical chemistry (journal) , materials science , composite material , chemistry , optoelectronics , chromatography , quantum mechanics , astronomy
To identify the composition of interstellar dust grains by their absorption spectra requires accurate knowledge of their optical properties. The presence of inclusions or voids within grains can alter their refractive indices. Here, we examine the suitability of applying the Maxwell‐Garnett mixing theory to highly porous grains. It is found that the effective refractive index obtained for heterogeneous grains depends upon the magnetic permittivities as well as the dielectric constants of its constituent materials. In the case of small grains (radii ∼1 μm ) consisting of a continuous material inter‐dispersed with a number of vacuous inclusions a relatively simple expression for the effective dielectric constant and magnetic permittivity is obtained, from which effective refractive index and absorption efficiency can be calculated. The absorption efficiency for porous, iron grains is calculated over the frequency range 0.5–10 GHz. For such grains, it is found that the absorption efficiency increases as the number of inclusions increases.