Variation of Radiation Effects and Signal Efficiency with Distance between Electromagnetic Source and Trunk Model

The concern on radiation effect and efficiency of wireless device are reemerged due to the increasing application of implanted and ingested bi-directional wireless devices. In this study, finite-difference time-domain (FDTD) method is applied to analyze the variation of biological effect and signal strength with distance between electromagnetic source and trunk model. FDTD simulations are carried out for 900 MHz system with a half-wavelength dipole antenna. The distance is changed from 25 mm to 1 mm within the range of lambda/2pi. Specific absorption rate (SAR) distributions for various vertical and horizontal slices of the human trunk are calculated. The computational results are interpreted in terms of international safety guidelines for human health, showing that the distance has less influence on the signal efficiency. However, peak SAR, the maximums of 1-g and 10-g averaged SAR values normalized to 2.5 mW input power decrease from 0.26 W/kg, 0.04 W/kg, and 0.0188 W/kg to 0.0158 W/kg, 0.0114 W/kg, and 0.008 W/kg respectively. Considering the link performance of wireless device and safety guidelines of radiation exposure, we recommend that the antenna outside body need to keep a suitable distance from human body. In this simulation, 12 mm is the optimized distance.