ID Number		1078
Study Type		Engineering & Physics
Model		Numerical FDTD models of children and adults and analysis of SAR distribution, VAR and temperature.
Details		Numerical modeling was used to determine and compare SAR from mobile phone exposure in the brains of children vs. adults. The model consisted of a multipole analysis of 3 layered (scalp/cranium/brain) spherical heads exposed to a nearby 0.4 wavelength dipole at 900 MHz. The authors determined from a literature search that there were no substantive age-related differences in tissue conductivity after the first year of life. However, it was also determined that the thickness of the ear, scalp, and cranium may increase with age. The model analysis revealed that compared to an average adult, the peak brain 10 g averaged SAR in mean 4, 8, 12 and 16 year old heads is increased by a factor of 1.31, 1.23, 1.15 and 1.07 respectively. However, the authors conclude that contrary to the advice of the UK Stewart Report, the relatively small scale of these increases does not appear to warrant any special precautionary measures for child mobile phone users since: a) SAR testing protocols provide a compensatory safety margin for the brain; b) the maximum worst case brain temperature rise in children using mobile phones is well within safe levels and normal physiological parameters, and; (c) the range of age average increases in children is less than the expected range of variation seen within the adult population. Authors' abstract: McIntosh and Anderson (2011): Basic restrictions for protecting against localized tissue heating induced from exposure to radiofrequency (RF) fields are typically specified as the specific energy absorption rate (SAR), which is mass averaged in recognition of the thermal diffusion properties of tissues. This article seeks to determine the most appropriate averaging mass (1, 3, 5, 7, or 10 g) and averaging shape (cube or sphere). We also consider an alternative metric, volumetric energy absorption rate (VAR), which uses volume averaging (over 1, 3, 5, 7, and 10 cm(3); cube and sphere). The SAR and VAR averaging approaches were compared by considering which was a better predictor of tissue temperature rise (”T) induced by near- and far-field RF exposures (0.5-6 GHz), calculated in a detailed human body model. For the exposure scenarios that we examined, VAR is better correlated with ”T than SAR, though not at a statistically significant level for most of the metric types we studied. However, as VAR offers substantive advantages in ease of assessment we recommend this metric over SAR. Averaging over a cube or a sphere provides equivalent levels of correlation with ”T, and so we recommend choosing the averaging shape on the basis of which is easier to assess. The optimal averaging volume is 10 cm(3) for VAR, and the optimal mass is 10 g for SAR. The correlation between VAR or SAR and ”T diminishes substantially at 6 GHz, where incident power flux density may be a better exposure metric.
Findings		Effects
Status		Completed With Publication
Principal Investigator		EME Australia Pty Ltd, Australia - vitas@ieee.org
Funding Agency		ACEBR, Australia
Country		AUSTRALIA
References		Anderson, V Phys. Med. Biol., (2003) 48:1-13 Anderson, V et al. Bioelectromagnetics, (1995) 16:60-69 McIntosh, RL et al. Bioelectromagnetics., (2011) 32:312-321 Anderson, V et al. Bioelectromagnetics., (2010) 31:454-466
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