# Analyzing the SAR in Human Head Tissues under Different Exposure Scenarios
## 3 Results and Discussion
### Simulation Results for Computational Human Models  
All measurements performed at the laboratory provide information about the average SAR value in the head region. In order to determine the SAR in the tissues of interest, it is necessary to measure the SAR over the equivalent liquid belonging to that tissue. Since this process is difficult and costly, the calculations can be made through simulations and using realistic computational human models. Since these models offer the opportunity to work with human models of different ages, gender, and heights, simulations with these models can provide more detailed calculations. In the simulations, realistic computational human models with different ages and genders were considered from the CST voxel family to investigate the effects of age and gender. Additionally, the dielectric properties of the tissues in these models were adjusted based on the operating frequency (900 MHz and 1800 MHz). In order to examine the effects of SAR on tissues in the head region, it is necessary to replace the SAM with a computational human model head while keeping the excitation signal level and the antenna position the same. The SAR 10g distribution of the whole head region of adult males is given in Figure 6 as an example. The SAR 10g values are calculated, and the peak SAR 10g values are saved and given for the head and for the selected tissues of all models. In order to determine how the same SAR affects other tissues of the head region, additional SAR calculations are made. The change of the SAR 10g as a function of E for the baby brain, fat, and muscle tissues at 900 MHz and 1800 MHz are shown in Figure 7a,b, respectively. As seen from Figure 7a, while all SAR 10g values are close to each other, there is a significant difference between the SAR 10g of the brain and the other SAR 10g values for 1800 MHz. The baby whole head and muscle tissue has the highest SAR compared with other tissues at 900 MHz and the lowest SAR can be observed over baby brain tissue at 1800 MHz, all of which were below the ICNIRP's limits. The highest SAR 10g is 1.02 W/kg and 1.75 W/kg for the head at 900 and 1800 MHz, respectively. It can also be concluded from the figures that the change in the frequency affects the SAR levels over tissues. The increase was at most 80% for the tissues of fat, muscle, and the whole head. Figure 8 shows the SAR 10g values of the child head and selected tissues at 900 MHz and 1800 MHz. As seen from the figure, the SAR 10g of child brain tissue is lower than other tissues and the head for 900 MHz and 1800 MHz. Furthermore, SAR 10g values of fat, muscle, and head are roughly the same. The head has the highest SAR 10g values of 1.42 W/kg and 3.67 W/kg at 900 MHz and 1800 MHz, respectively. It can also be concluded from the figure that the SAR 10g value of the head is 1.76 times higher than brain tissue for 900 MHz and 2.60 times higher for 1800 MHz. SAR 10g values of brain, fat, muscle, and head are below the limits for 900 MHz while some SAR values (i.e., 2.05, 2.85, 2.95, 3.34, and 3.67 W/kg) are above the determined limits for fat, muscle and head at 1800 MHz. Figure 6: SAR 10g distribution over the adult male computational human model. SAR 10g values of the adult female are illustrated in Figure 9. Some of the SAR 10g values are also above the limits at 1800 MHz, similar to the child SAR 10g. As can be seen from the figures, and contrary to those of baby and child, the SAR 10g values differ from each other. The highest SAR 10g is observed for the head at 1.57 and 4.46 W/kg for 900 MHz and 1800 MHz, respectively, as obtained from the baby and child head. The brain tissue SAR 10g value is the lowest among them. Figure 8: SAR 10g values of head and selected tissues of a child, (**a**) 900 MHz and (**b**) 1800 MHz. Figure 7: SAR 10g values of head and selected tissues of baby, (**a**) 900 MHz and (**b**) 1800 MHz. **Figure 9.** SAR 10g values of head and selected tissues of adult female, (**a**) 900 MHz and (**b**) 1800 MHz.