## 4 Thermal Management of Heat Transfer in 5G Networks Technology
[PERSON] et al., 2015 [75], conducted an experimental investigation on the thermal performance of several PCM-based heat sink cases, using pure PCM, silicone-PCM composites, and graphite-PCM composites. Their research findings illustrated how PCM can significantly reduce overall temperatures. [PERSON] et al., 2024 [76], discussed the important role of various materials, such as hydrogels, metal-organic frameworks, and PCMs, in dissipating heat in 5G-enabled portable electronics in addition to their potential challenges and improvements. Different thermal and electromagnetic (EM) simulations of several antenna (or chip) layouts in planar AESA's were conducted and presented in the literature by [PERSON] et al., 2018 and [PERSON] et al., 2019 [67; 78; 77]. For example, simple patch antennas were used by the authors in their simulations (see Figures 4-6). The simulation settings in and realization of the 3D model were described and the thermal and EM performances of a single element in a unit cell was studied. Both EM and thermal considerations are jointly incorporated in the optimization of array layouts, with a novel connection established between layout sparsity and thermal management. [PERSON] et al., 2018 and 2019 [67; 78; 77], showed that fully passive cooling can be achieved by attaching CPU fanless coolers to the  
passive antenna system that is integrated into sandwich walls in energy-efficient buildings. [PERSON] et al. (2013) [79] employed a three-dimensional finite element method (FEM) in steady-state thermal analysis. Their investigations primarily covered three types of walls: a sandwich wall, a signal-transmissive wall with stainless steel as connector (new design), and a signal-transmissive wall with copper (old design). In their research, [PERSON] et al. (2013) [79] conducted three-dimensional heat transfer simulations (see Figures 7 and 8) to determine the thermal transmittance (U-values) of 5G antenna walls. Their results revealed that, using stainless steel as the connector material (new design), the U-value rose from 0.1496 (for the wall without antenna) to 0.156 W/m\({}^{2}\)K, leading to an additional heating loss per year of only 0.545 KWh/m\({}^{2}\) in Helsinki. In contrast, with the old design that used copper as the connector material, the U-value increased dramatically to 0.3 W/m\({}^{2}\)K, exceeding the National Building Code of Finland's limit of 0.17 W/m\({}^{2}\)K and causing additional heat loss of 12.8 KWh/m\({}^{2}\) (23.5 times more than the new design). The new design significantly reduced the thermal bridging effects. An intelligent AI model for the heat transfer modeling of 5G Smart Poles was developed by [PERSON] et al., 2021 [80]. The authors ensured heat balance across three different surfaces of a cylindrical utility box; they covered the side exposed to solar radiation, the side where the electrically heated plate is located within the cylinder, and the side that represents the shaded side of the cylinder. Figure 9 shows an example of the integration of the AI model of [PERSON] et al., 2021 [80], into the thermal design process of base station in order to intelligently control the heat flow and the maximum temperature. The input parameters they utilized for developing their AI model (see Figure 9) were as follows: the station's latitude, ambient temperature, internal air flow-rate, and time. The used these parameters to forecast the local heat flow in Watts and the maximum temperature of the plate within the utility box (see Figure 9). The findings of [PERSON] et al., 2021 [80],  
Figure 8: Enhanced local heat flow lines thanks to numerical modeling and design. (**a**) Nine-signal-transmissive wall with stainless steel (new design); (**b**) nine-signal-transmissive wall with copper (old design) [79]. Figure 7: Sandwich wall: ultra-wide-band back-to-back in wall spiral antenna system with two identical spiral antennas and a semi-rigid dual coaxial cable.