Authors
Chen HY, Chuang CY.  (2009). Currents Induced in Human Bodies during Radiofrequency Exposure near a Cellular Phone Base Station.  Electromagnetics 29(1) 13-23.

Background
Radiofrequency (RF) energy may result in high levels of induced currents through a human body close to cellular phone base station antennas. Because of its relationship to the specific absorption rate (SAR), the induced current is an important parameter for assessing potential health hazards. While several theoretical and experimental evaluations have been conducted of the currents induced in the human body by electromagnetic fields (EMFs) with frequencies below 300 MHz, there is still much unknown about the currents induced by frequencies over 300 MHz.

Objective
The objectives of this study were to conduct computations of currents induced in human feet near a cellular phone base station antenna, to compare the computation results with those obtained by measurement, and to obtain layer current distributions in the human body based on computer simulations.

Methods
Computation of induced currents for frequencies over 600 MHz is difficult because it requires excessive amounts of computer storage. Therefore, the finite-difference time-domain (FDTD) method, which can be applied to complex configurations and requires smaller computer storage, was selected for the computations. Foot currents were measured under two conditions: when a man was wearing shoes and when standing barefoot. Computations of induced currents were done for a human model with and without clothes.

Results and interpretation
There was a good agreement between the measurement data and the computation results. The maximum values of foot current were 20.73 mA and 18.51 mA for measurements and calculations respectively, and these maximum values were obtained for a human standing barefoot 10 meters from the cellular phone base station. Within 10-30 metres from the base station, the average foot current was less than 11.07 mA. Wearing shoes reduced the foot current. The reduction factor was 0.72-0.91 based on measurements and 0.80 based on the FDTD method. According to the computer simulations, the highest layer currents distributed in the body occurred in the area of the chest. From the layer current profiles, it was estimated that the maximum induced body current density was below the excitation threshold level of 1 mA/cm2. Layer currents distributed in most parts of the human body were the same for both the shoe wearing and standing barefoot models, and there was only a small difference in the magnitude of current distributions between the human model with and without clothes.

Conclusion
From simulations and measurement results of foot currents, it was found that the theory and the experiment were in good agreement. Lack of measurement data on layer current distributions in most parts of the human body makes it difficult to compare the current distributions for the numerical results and measurement data. However, the FDTD method offers a possibility of obtaining current distributions in the human body and provides a simple and inexpensive method to evaluate SAR distributions for various standards and safety guidelines.

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