SAR versus VAR, and the size and shape that provide the most appropriate RF exposure metric in the range of 0.5-6 GHz

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Title: SAR versus VAR, and the size and shape that provide the most appropriate RF exposure metric in the range of 0.5-6 GHz
Author(s): McIntosh, Robert L.; Anderson, Vitas
Abstract: 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 cm3; cube and sphere). The SAR and VAR averaging approaches were compared by considering which was a better predictor of tissue temperature rise (ΔT) 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 ΔT 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 ΔT, and so we recommend choosing the averaging shape on the basis of which is easier to assess. The optimal averaging volume is 10 cm3 for VAR, and the optimal mass is 10 g for SAR. The correlation between VAR or SAR and ΔT diminishes substantially at 6 GHz, where incident power flux density may be a better exposure metric.
Publication type: Journal article
Research centre: Swinburne University of Technology
Source: Bioelectromagnetics, Vol. 32, no. 4 (May 2011), pp. 312-321
Publication year: 2011
FOR Code(s): 020302 Electrostatics and Electrodynamics; 110202 Haematology; 111705 Environmental and Occupational Health and Safety
Keyword(s): Human body modeling; Mass averaging; Radiofrequency safety standards; Temperature rise; Volume averaging
Publisher: John Wiley & Sons
ISSN: 0197-8462
Publisher URL: http://dx.doi.org/10.1002/bem.20642
Peer reviewed