## 3 Materials and Methods
### Scenario of the Incidence of SAR and Temperature Variation on Human Tissues in Indoor Environments
The limits for SAR values were determined between 10 Hz and 10 GHz, taking 1 g of tissue and 10 g of exposed organ or the whole body as a reference. The value chosen falls within a frequency range where absorbed electromagnetic energy should not cause thermal damage to human tissue. SAR limits were differentiated according to the work environment, which can be indoor or outdoor. Table 2 shows the limits set for the work environment and public areas [54]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Bands MHz** & & **Skin** & **Fat** & **Bone** & **Brain** \\ \hline LTE 800 & \(\epsilon_{r}\) & 41.66 & 5.47 & 12.51 & 46.04 \\
805.95 & \(\sigma\) & 0.83 & 0.04 & 0.12 & 0.73 \\ \hline ETC 1 & \(\epsilon_{r}\) & 41.44 & 5.46 & 12.46 & 45.84 \\
873 & \(\sigma\) & 0.84 & 0.04 & 0.12 & 0.73 \\ \hline GSM 900 & \(\epsilon_{r}\) & 41.26 & 5.45 & 12.41 & 45.67 \\
948.05 & \(\sigma\) & 0.88 & 0.05 & 0.14 & 0.79 \\ \hline ETC 2 & \(\epsilon_{r}\) & 40.05 & 5.39 & 12.10 & 44.56 \\
1383.05 & \(\sigma\) & 1.03 & 0.06 & 0.21 & 0.97 \\ \hline LTE 1800 & \(\epsilon_{r}\) & 38.83 & 5.33 & 11.76 & 43.32 \\
1849.5 & \(\sigma\) & 1.20 & 0.07 & 0.28 & 1.17 \\ \hline WLAN & \(\epsilon_{r}\) & 38.04 & 5.28 & 11.38 & 42.53 \\
2441.5 & \(\sigma\) & 1.45 & 0.10 & 0.39 & 1.50 \\ \hline
4G & \(\epsilon_{r}\) & 38.2 & 4.8 & 14.5 & 48 \\
2600 & \(\sigma\) & 0.6 & 0.05 & 0.025 & 1.3 \\ \hline
5G & \(\epsilon_{r}\) & 35 & 4.5 & 14 & 45 \\
26,000 & \(\sigma\) & 0.7 & 0.06 & 0.03 & 1.4 \\ \hline \(\rho\) (density) (Kg/m\({}^{3}\)) & & 1100 & 920 & 1850 & 1030 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Electrical properties of human tissue. Figure 3: Electric field limit values determined by ICNIRP and HHI for humans. After determining the electrical properties shown in Tables 1 and 2, which link the interaction of electromagnetic field radiation with human tissue, the electronic system implemented for the acquisition and monitoring of SAR and temperature variation was introduced. Electronic System for the Acquisition and Monitoring of SAR and Temperature Variation on Human Tissues  
The impact of electromagnetic fields (800 MHz-26 GHz) on human tissues depends on the monitored body area, subject height, and movement within the work environment. To assess these parameters, an integrated hardware/software system was designed for indoor monitoring. The electronic system ensured the effective measurement of specific absorption rate (SAR) and temperature variations. The monitoring device, managed by a Raspberry Pi via the I\({}^{2}\)C protocol, acquired and processed sensor data. The SAR sensor, a redundant strain sensor with a LIN bus interface, consisted of strain gauges on a steel support and included a temperature compensation feature. It operated with a 7-18 V power supply, consuming a maximum of 20 mA, within a temperature range of \(-\)20 to +70 \({}^{\circ}\)C. Its compact size (95 mm \(\times\) 95 mm \(\times\) 54.5 mm) allowed flexible application, though in this study, it was not used directly on individuals. Temperature data were captured using an infrared sensor. The Raspberry Pi transmits data to a cloud platform via Wi-Fi, enabling real-time remote monitoring. The system's acquisition and resolution process are outlined in Figure 4, providing a structured approach to SAR and thermal data analysis. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Whole Body Average** & **Localized SAR** & **Localized SAR** \\  & **SAR (W/Kg)** & **(Head and Trunk)** & **(Limbs) (W/Kg)** \\ \hline FCC (1 g) & & & \\ Occupational Exposure & 0.4 & 8 & 20 \\ General Public Exposure & 0.08 & 1.6 & 4 \\ \hline CE (10 g) & & & \\ Occupational Exposure & 0.4 & 10 & 20 \\ General Public Exposure & 0.08 & 2 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Electrical characteristics of the developing layers. Figure 4: Flowchart monitoring system. To design the device capable of detecting SAR and body temperature in indoor environments, technologies for electromagnetic and thermal measurement were integrated.