Autores
Akimoto S, Nagaoka T, Saito K, Watanabe S, Takahashi M, Ito K. (2010). Comparison of SAR in realistic fetus models of two fetal positions exposed to electromagnetic wave from business portable radio close to maternal abdomen. Conf Proc IEEE Eng Med Biol Soc. 1:734-7.

Introduction
Exposure to radiofrequency (RF) emitting devices has increased rapidly in the last few years and the health effects of RF are dependent on two factors; frequency and strength of the microwaves. Specific absorption rate (SAR) is a measure used to evaluation the exposure. WHO considers that one important research area is the assessment of RF exposure to the fetus in pregnant woman. In this study, a numerical model of a 26th gestational week pregnant Japanese woman was used.

Objective
The objective of the dosimetric study was to compare the SARs of two fetal positions (using two different numerical models) exposed to radiofrequency fields emitted from a normal mode helical antenna with a metallic case.

Methods
The numerical models previously developed by the research team included a fetus position in the left occiput anterior (model A) and one in the right sacro anterior (model B) of the model’s pelvis. The finite-difference time domain (FDTD) method was used to calculate the electric field around the antenna, a business portable radio with a monopole type normal mode helical antenna and a small radio terminal. The normal helical antenna was positioned on the right side of model’s waist (case 1) and left side (case 2). The power from the antenna was 5.0 W.

Results and Interpretation
The fetus-averaged SAR was higher in case 1 than case 2 in model B (left occiput anterior) but SAR was higher in case 2 compared to case 1 in model A (right sacro anterior). The highest recorded SAR was 0.14 W/kg in case 1 of model B which could be explained by the higher conductivities of the placenta and amniotic fluid. Also, in both models A and B, 10g-averaged SARs were higher in case 1 than case 2. The values recorded for all the different antenna positions were lower than the guideline value for general public exposure (2 W/kg) and occupational exposure (10 W/kg) set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). These results indicate that changes in fetal SAR depend on distance and penetration path from the emitting antenna and fetal surface which varies depending on the position.

Conclusion
It was concluded that all measured SARs were lower than the RF safety limits established by ICNIRP. The authors will continue to evaluate in another experiment SAR in fetus using different fetal positions and temperature elevation of the fetus as what they used in this study.

 



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