Attenuation Characteristics of the SAR in a COST244 Phantom with Different EM Source Locations and Sizes

Shoichi KAJIWARA  Atsushi YAMAMOTO  Koichi OGAWA  Akihiro OZAKI  Yoshio KOYANAGI  

Publication
IEICE TRANSACTIONS on Communications   Vol.E88-B   No.6   pp.2391-2400
Publication Date: 2005/06/01
Online ISSN: 
DOI: 10.1093/ietcom/e88-b.6.2391
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on 2004 International Symposium on Antennas and Propagation)
Category: 
Keyword: 
SAR,  attenuation characteristic,  COST244 phantom,  lossy medium,  spatial spread of energy,  

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Summary: 
This paper addresses the variation of the attenuation characteristics of the Specific Absorption Rate (SAR) in a lossy medium as a function of the distance between an antenna and the medium with different EM-source sizes. Analysis and measurements were performed using a dipole antenna at 900 MHz and a COST244 cubic phantom. From this, an empirical equation has been derived, representing the attenuation characteristics of the SAR. The equation takes into consideration an energy loss due to the spatial spread of electromagnetic waves. In the case where an antenna is placed more than λ/2π away from the medium, the attenuation characteristics of the SAR are those obtained from plane waves in the lossy medium. In the case where a half-wavelength dipole antenna is located close to the medium, at a distance of less than λ/2π, the attenuation characteristics of the SAR are calculated from an equation that includes a loss caused by the spread of energy as a cylindrical wave. Moreover, when the length of antenna is short, it is found that a spatial attenuation factor appropriate to a spherical wave should be taken into account.