Authors
Wu T, Hadjem A, Wong MF, Gati A, Picon O, Wiart J. Whole-body new-born and young rats' exposure assessment in a reverberating chamber operating at 2.4 GHz. Phys Med Biol. Feb 24, 2010;55(6):1619-1630. Ahead of print.

Introduction and Objective
The World Health Organization (WHO) has set sensitivity of children to electromagnetic fields (EMF) as a research priority. In line with this, a project has been initiated with the objective to study the effects of in utero and post-natal exposure of rats to Wi-Fi signals. Studies of radiofrequency radiation exposure on experimental animals often involve restrain of animals in various systems. In this respect, the reverberating chamber (RC) has the advantage of non-restrained whole-body exposure of experimental animals. To determine the power absorption, numerical methods, in particular finite difference time domain method (FDTD) is often used. In case of exposure in reverberating chamber, enclosure absorption is weak, and FDTD is facing a very slow convergence. To overcome this limitation, the authors developed a hybrid approach combining measurement and FDTD simulations. Using this approach, they analyzed the whole body specific absorption rate (SAR) of pregnant, new born and young rats for different configurations and ages.

Methods
The reverberating chamber is a cube (edge length of 1.5 metres) with a two-stage plastic test bench installed in the middle to place two EMF transparent boxes on each stage. The antennas are located on each interior wall of the reverberating chamber. At each time, only one antenna randomly selected by software is active. Measurement points for measuring time-averaged power are distributed on each stage of the test bench. The numerical rat model used in this study was composed of 36 tissues; its weight was 375 grams. Comparative simulations were conducted with resolutions of 1 and 2 mm. Based on anatomical observations and measurements, models for different ages were developed. The embryos were modeled by small spherical models of 0.6 cm, 1 cm and 2 cm in diameter (for different ages of the embryos) covered with a layer of amniotic liquid. To account for significant changes during the first 30 days after birth, a scaled reduction of the adult model was used. Evolution of dielectric properties with age was considered in the simulations. Whole-body SAR was computed for heterogeneous and homogeneous rat model. Age-related changes in animal behavior/movements (studied using a camera installed in the reverberating chamber) were also considered.

Results and Interpretation
Using the hybrid approach, the relationship between the whole-body SAR and the input power delivered to the reverberating chamber was documented. The variations in the whole-body SAR introduced by application of different computational parameters were as follows: the difference in model resolution (1 mm vs. 2mm) ±3%, homogeneous vs. heterogeneous model ±4.77%, dielectric parameters ±3%, intra-species differences (in weight) ±5.00%, postures ±3.00%, behaviors – up to ±34% at 16 days of age.

Conclusion
Using the approach combining measurement and FDTD simulations, the authors have characterized the exposure to a Wi-Fi signal of freely moving rats from the gestation period to 30 days after birth.


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