Authors

Findlay RP and Dimbylow PJ. (2010). SAR in a child voxel phantom from exposure to wireless computer networks (Wi-Fi). Phys. Med. Biol. 55(15):N405-N411.

Introduction
The exposure to wireless computer networks (Wi-Fi) in schools has raised concerns regarding potential health risks due to exposure to radiofrequency field radiation. Research on exposure from mobile phones is abundant but very few studies on Wi-Fi access points or Wi-Fi-enabled PCs have been published so far.

Objective
The objective of the study was to calculate SAR’s in a 10 year old version of the NORMAN (NORmalized MAN) voxel phantom at 2.4 GHz and 5 GHz frequencies.

Methods
Three Wi-Fi scenarios were set-up to calculate SAR; exposure to plane waves, half-wave dipoles, and antennas mounted on a laptop PC. The model used was in a sitting posture and scaled to International Commission on Radiation Protection (ICRP) dimensions of a 10 year old child. The finite-difference time-domain (FDTD) method was used to calculate the SAR values. A set of plane-wave calculations was used to determine exposure from Wi-Fi access points. Half-wave dipoles were modelled to determine human exposure from Wi-Fi antennas in personal computers (PCs). An inverted-F antenna mounted on a circuit board with a laptop PC was used to determine the typical Wi-Fi exposure configurations.

Results
The highest results of plane-wave calculations were in antero-posterior exposure. Peak localized SAR values (averaged SAR10g) were determined for each exposure condition. The SAR varied from 341 to 511 μW kg−1 for 2.4 GHz and from 352 to 451 μWkg−1 for 5 GHz. Peak localized SAR values were determined for half-wave dipoles at the chest and head heights. The lowest SAR calculated was 0.180 W kg−1 in the head for a 2.4 GHz antenna at a distance of 31 cm from the face. The highest value obtained was 8.17 W kg−1 in the head at a separation of 3 cm. The public basic restriction recommended by ICNIRP for localized SAR in the head is 2 Wkg−1 at 2.4 and 5 GHz, thus 81.7 mW kg−1 is well below the ICNIRP restrictions. In measurements of the PC with antenna with a typical Wi-Fi exposure scenario, the maximum localized SAR in the body occurred for the antenna positioned bottom right at 5 GHz. A value of 0.937 Wkg−1 per W was obtained in the hands. In the torso, the localized SAR varied between 0.551 mW kg−1 and 3.99 mW kg−1. The ICNIRP restriction is very protective of the public since 3.99 mWkg−1 is considerably below basic restrictions of 2 Wkg-1.

Interpretation and Conclusion

SAR values were determined in a 10 year old sitting voxel model exposed to EMF at frequencies of 2.4 and 5 GHz. The highest whole-body averaged SAR value found for plane-wave exposure was 19.1 μW kg−1 for a 1 V m−1 incident field. Measured values of electric fields from Wi-Fi access points at 1 metre were less than 2 Vm−1 and well below the public ICNIRP basic restrictions of whole-body averaged SAR which is 64.7 Vm-1. The highest localized SAR (8.17 W kg−1 per W) was determined to be in the head for a 2.4 GHz dipole antenna at 3 cm distance and 100% duty factor. In more realistic exposure conditions, the peak localized SAR was calculated at 1.8 mW kg−1 and again well below the ICNIRP basic restriction on localized SAR of 2 W kg−1.  


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