## 6 Modeling for SAR Simulation  
With the use of a computer model, it is feasible to thoroughly analyze \(SAR\) in the human body. This model may be used to research the effects of mobile phones on the human head since it can be used to visualize the processes of tissue absorption and heat deep within the human body. The characteristics of human tissues can be altered to imitate various age groups. The numerous tissues and bones that make up the human head model each have unique electromagnetic energy-absorption properties. A mobile phone's characteristics can be changed to emulate various GSM device models. Numerous factors, including the antenna radiation pattern, transmitted signal strength, and signal frequency, are modifiable. The computer model's ability to see the depth of the human head, which can be utilized to analyze the absorption and warming processes in depth, is its most important feature. For the proper functioning of the model, it is essential to know the biological characteristics of human tissues. The human body is composed of many organs and characterized by specific biological parameters that must be taken into account correctly in the model. The electromagnetic characteristics of the dielectric constant, magnetic permeability, and conductivity [18] should be properly defined for each modeled organ. The created computer model uses parameters that characterize the biological tissues of an adult. The shape of the human head was applied by the IEEE library and was loaded into the COMSOL Multiphysics software. The model was imported from a file named sar_in_human_head_mphbin [19; 20]. The source of electromagnetic radiation was a model of a smartphone that was manually added. In the considered model, the location of the device was chosen to be on the left side of the head in order to facilitate the comparison of the obtained results with thermal images from our previous experimental studies. The mobile device was modeled at a distance of 1 cm from the head as shown in Figure 1.  
The electromagnetic parameters of the biological tissues of the human head were modeled through an interpolation function that uses the characteristics of the tissue inside the human head. The output for this function is directly taken from a file named sar_in_human_head_interp.txt. After simulation of the model, it is possible to estimate the \(SAR\) on any shape and tissue of the human body. When designing mobile devices, it is important to determine the amount of radiation that can be absorbed by the human body. The use of COMSOL Multiphysics and its radio frequency module allows a faster and more-efficient approach in the design of wireless devices that meet certain safety requirements. The local SAR value in the human head, calculated using the 900 MHz frequency equation, is shown in Figure 2.  
When talking to a mobile phone, the human head is very close to the phone, and the power of the emitted electromagnetic field is very high. Penetrating into a person's head, the electromagnetic field releases some of its energy, and the tissues in the head absorb this energy. Electromagnetic energy affects the particles in the tissue due to the  
Figure 1: (**a**) and (**b**) Human head model and mobile device. Figure 2: \(SAR\) visualization. electrical and magnetic components of the electromagnetic field. Visualization of the effects of penetration of the electromagnetic wave into the human head can be shown by means of incisions of the head at certain levels (Figure 3). The strongest influence of the electromagnetic waves is in the head area, located in the immediate vicinity of the mobile device [17]. The greatest amount of energy is absorbed in this area, and the penetration into the human head is the greatest. The effects of exposure of the human body to radio frequency radiation mainly depend on the exposure time and the strength of electromagnetic fields. The penetration of the electromagnetic field into the depths of the human head depends on the frequency of the carrier signal.