## 3 Specific Absorption Rates and Radiated Power Density in the Vicinity of the Structures Analyzed  
The values of the specific absorption rate were determined for three types of tissue considered to be close to the analyzed antenna, namely skin, muscle and fat. The values that resulted after numerical modeling of the model are analyzed and compared with the ones suggested by the ICNIRP (International Commission on Non-Ionizing Radiation Protection). The skin is considered to have a thickness of 4 mm, and the fat is also 4 mm thick, while the muscle tissue is considered to be the widest, 30 mm. The characteristic parameters considered are presented in Table 7. Due to the applications which are mainly situated next to or even on the human tissues, two cases are considered: one where the antennas are placed on the tissue, and the other where the antennas are at a distance of 4 cm from the antennas [19; 20]. The SAR values for general public exposure for more than 6 min is 2 W/kg in the case of the head/torso and 4 W/kg in the vicinity of limbs. For the study, the tissues were considered as seen in Figure 17. A transversal section was performed in the tissue to observe the distribution of SAR in the YZ plane for both the initial and optimized structure, and it can be seen that when the structure is placed on the tissues, the values imposed by the standard are highly exceeded; thus, the antenna must be placed further from the human body. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Types of Tissue** & & & \\ \hline  & **Relative Permittivity** & **Conductivity** & **Loss Tangent** \\ \hline Skin & 38 & 1.46 & 0.283 \\ Fat & 5.28 & 0.1 & 0.145 \\ Muscle & 52.7 & 1.74 & 0.242 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Characteristic parameters for the considered tissue types. Figure 17: Antenna with the 3 different tissues: (**a**) antenna placed on the skin; (**b**) antenna at a distance of 4 cm from the tissues. In Figure 18, the representation of SAR in the YZ transversal section can be seen. The limits imposed by the standard are exceeded in all the tissue layers for both the initial structure of the antenna and the optimized antenna. The representation of SAR in each of the tissue layers, namely skin, adipose tissue and muscle, can be seen separately in Figure 19. The limits are exceeded in each layer in a wider area for the skin tissue, but they are smaller for the other tissue types. When the tissues are considered to be at a distance of 4 cm, the results are better, the SAR values being exceeded only in the skin tissue; thus, the solution to be in the standard  
Figure 19: SAR distribution in the tissue layers for the initial and optimized antenna: (**a**) skin; (**b**) adipose tissue; (**c**) muscle. Figure 18: SAR distribution on YZ transversal plane for: (**a**) initial antenna; (**b**) optimized antenna. limits would be to place the antenna at a distance larger than 4 cm from the human tissues, as it can be observed in Figure 20.  
The values of SAR change based on the material characteristics, making it an important parameter that can be used also in applications such as the mapping of snow covering some regions [29], crop mapping [30,31], flood [32] or terrain mapping [33], giving our antenna purposes if the values exceed the ones that are accepted according to the standards in force for the antenna to be in the close vicinity of the human body or embedded in its clothes or near equipment. According to [28], there are a few reports regarding the limits of the radiated power density of antennas, and there are different limits for different regions or countries.