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: 2.7). 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.

  • [Show abstract] [Hide abstract]
    ABSTRACT: In order to assess the compliance of Ingested Wireless Device (IWD) within safety guidelines, the Specific Absorption Rate (SAR) and near fields of IWD in two realistic human body models whose dielectric values are changed from the original by ±±10 and ±±20% are studied using the Finite-Difference Time-Domain (FDTD) method. The radiation characteristics of the IWD in the human body models with changed and original dielectric values are compared. Simulations are carried out at 13 scenarios where the IWD is placed at center positions of abdomens in the two models at the operation frequency of 1200 MHz. Results show that variation of the radiation intensity near the surface of abdomen is around 3.5 dB within 20% variation of dielectric values. Electric fields in the anterior of the human body models are higher than those in the posterior for all scenarios. SAR values increase with the increase of conductivities of human body tissues and usually decrease with the increase of relative permittivities. The effect of the dielectric values of human body on SAR is orientation, human body and frequency dependent. A variation up to 20% in conductivities and relative permittivities alone or simultaneously always causes a SAR variation less than 30%. As far as the compliance of safety was concerned, the IWD was safe to be used at the input power lower than 8.4 mW according to IEEE safety standards.
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper evaluates the variability of specific absorption rate (SAR) in the human eye. This variability results from changes in ocular axial length (OAL), which is common in many ophthalmologic and vision abnormalities, including myopia. A generic eye model was reconstructed according to published data. The feasibility of using the generic model in numerical research of electromagnetic fields (EMF) was demonstrated by means of comparative simulations with eye models reconstructed from magnetic resonance (MR) scans. Free-form deformation (FFD) was used to deform the OAL of the generic eye model. Thus, 64 deformed eyes were created and were categorized according to the OAL increase. The finite-difference time-domain (FDTD) method was applied in the simulations. The results revealed that changing the OAL does not increase EMF absorption in the eyes or the eye tissues. No additional induced temperature rise was produced by the changes of OAL. The results also indicated that the non-pathological increment of the OAL, which is inevitable during the childhood, does not increase the SAR in the eyes. Bioelectromagnetics. © 2014 Wiley Periodicals, Inc.
    Bioelectromagnetics 02/2014; · 2.02 Impact Factor


Available from