Sensitivity Evaluation of SAR on Size and Permittivity for Rat Brains Exposed to Microwaves at Mobile-Phone Frequency Bands Using the FDTD Method

The objective of this study is to evaluate the effect of size and permittivity on the specific-absorption-rate (SAR) values of rat brains during microwave exposure at mobile-phone frequency bands. A finite-difference time-domain (FDTD) technique with the perfect-matching-layer (PML) absorbing boundaries is used for this evaluation process. A color-coded digital image of the Sprague-Dawley (SD) rat based on magnetic resonance imaging (MRI) was used in FDTD calculation with appropriate permittivity values corresponding to different organs. The sizes of the digital models for 3, 4, 7, and 10 weeks-old rats were obtained by measurements. This study comprises three major parts. Firstly, the rat-model structure has been scaled uniformly; i.e., the rat size was increased without change of permittivity. The simulated SAR values were compared with other experimental and numerical results. Secondly, the effect of permittivity on SAR values has been examined by simulating the microwave exposure on rat brains with various permittivity values for a fixed rat size. Finally, the SAR distributions in depth and the brain-averaged SAR values were computed during the microwave exposure on a rat-model structure when both size and permittivity have varied corresponding to different ages ranging from 3 to 10 weeks. The simulation results show that the brain averaged SAR values increased about 50% for size-only change from 10-weeks to 3-weeks rat model, while those increased only about 12% for permittivity-only change. It was found that the brain-averaged SAR values increased about 63% in case of the change of the size and permittivity together.