A Comparison of Specific Absorption Rates in SAM Phantom and Child Head Models at 835 and 1900 MHz

Abstract

The specific absorption rates (SARs) in 7-year-old Korean, and 5- and 9-year-old European child head models were evaluated and compared with those of the specific anthropomorphic mannequin (SAM) phantom for mobile phone exposure at 835 and 1900 MHz. Compression of the pinnae was also considered for the 5- and 7-year-old child models during the evaluation. The cheek and tilt positions occurring when the earpiece of the phone is placed at the ear entrance canal (EEC) were analyzed against the same positions occurring when the earpiece is placed at the ear reference point (ERP). SAR variations were investigated for different skin and fat properties, as well as for different internal fat and muscle morphologies in the tissue area near the phone. A basic phone model with a monopole antenna was used for SAR calculation at each frequency. A phone model with a planar inverted F antenna was also used for verification, since the SAR results in the child models were higher than those in the SAM phantom at 1900 MHz. The spatial peak 10-g SAR values in all tissue including the pinnae and head-only were normalized to a forward power of 1 W at the feedpoint of the phone. Our results can be summarized as follows. First, a compressed pinna did not show significant changes in SAR values at 835 MHz; however, at 1900 MHz, there was an average 25% increase in spatial peak 10-g SARs for pinna-excluded tissue and a 29% increase for pinna-included tissue. Second, a phone earpiece placed at the EEC provided higher SARs in many cases compared to placement at the ERP. Third, the peak 10-g SAR was found to be very sensitive to the fat and muscle structure under the skin when touched by the mobile phone; a muscle-dominant internal head structure led to a higher peak 10-g SAR. Finally, the SAM phantom does not seem to provide a conservative estimation of child head exposure at 1900 MHz; 45% (pinna-excluded: IEEE Std C95.1) and 75% (pinna-included: ICNIRP guidelines) of the 40 total cases we reviewed showed higher SAR results than the SAM phantom.