The effect of increase in dielectric values on specific absorption rate (SAR) in eye and head tissues following 900, 1800 and 2450 MHz radio frequency (RF) exposure

Technology Platforms, Nokia Corporation, PO Box 301, FIN-00045 Nokia Group, Linnoitustie 6, 02600 Espoo, Finland.
Physics in Medicine and Biology (Impact Factor: 2.92). 04/2006; 51(6):1463-77. DOI: 10.1088/0031-9155/51/6/007
Source: PubMed

ABSTRACT Numerous studies have attempted to address the question of the RF energy absorption difference between children and adults using computational methods. They have assumed the same dielectric parameters for child and adult head models in SAR calculations. This has been criticized by many researchers who have stated that child organs are not fully developed, their anatomy is different and also their tissue composition is slightly different with higher water content. Higher water content would affect dielectric values, which in turn would have an effect on RF energy absorption. The objective of this study was to investigate possible variation in specific absorption rate (SAR) in the head region of children and adults by applying the finite-difference time-domain (FDTD) method and using anatomically correct child and adult head models. In the calculations, the conductivity and permittivity of all tissues were increased from 5 to 20% but using otherwise the same exposure conditions. A half-wave dipole antenna was used as an exposure source to minimize the uncertainties of the positioning of a real mobile device and making the simulations easily replicable. Common mobile telephony frequencies of 900, 1800 and 2450 MHz were used in this study. The exposures of ear and eye regions were investigated. The SARs of models with increased dielectric values were compared to the SARs of the models where dielectric values were unchanged. The analyses suggest that increasing the value of dielectric parameters does not necessarily mean that volume-averaged SAR would increase. Under many exposure conditions, specifically at higher frequencies in eye exposure, volume-averaged SAR decreases. An increase of up to 20% in dielectric conductivity or both conductivity and permittivity always caused a SAR variation of less than 20%, usually about 5%, when it was averaged over 1, 5 or 10 g of cubic mass for all models. The thickness and composition of different tissue layers in the exposed regions within the human head play a more significant role in SAR variation compared to the variations (5-20%) of the tissue dielectric parameters.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper a parametric study on characteristics of a planar metal antenna in vicinity of a homogenous human head at 900 MHz and 1800 MHz are carried out. Initially the planar metal antenna is designed at 900 MHz and 1800 MHz. The impedance and radiation characteristics of these antennas are shown in free space and in proximity of a human head. Also Specific Absorption Rate (SAR) for different distances of the antenna from head are evaluated and compared.
    C3IT 2012, Academy of Technology, Hooghly, West Bengal, India; 02/2015
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents finite-difference time-domain (FDTD) calculations of specific absorption rate (SAR) values in the head under plane-wave exposure from 1 to 10 GHz using a resolution of 0.5 mm in adult male and female voxel models. Temperature rise due to the power absorption is calculated by the bioheat equation using a multigrid method solver. The computational accuracy is investigated by repeating the calculations with resolutions of 1 mm and 2 mm and comparing the results. Cubically averaged 10 g SAR in the eyes and brain and eye-averaged SAR are calculated and compared to the corresponding temperature rise as well as the recommended limits for exposure. The results suggest that 2 mm resolution should only be used for frequencies smaller than 2.5 GHz, and 1 mm resolution only under 5 GHz. Morphological differences in models seemed to be an important cause of variation: differences in results between the two different models were usually larger than the computational error due to the grid resolution, and larger than the difference between the results for open and closed eyes. Limiting the incident plane-wave power density to smaller than 100 W m(-2) was sufficient for ensuring that the temperature rise in the eyes and brain were less than 1 degrees C in the whole frequency range.
    Physics in Medicine and Biology 07/2009; 54(11):3393-404. DOI:10.1088/0031-9155/54/11/008 · 2.92 Impact Factor


Available from