# Estimation of SAR Average in Rats during 5G NR Chronic Exposure
## 4 Discussion  
Table 1 shows a discrepancy between theoretical estimates and numerical simulations in the case of non-distributed absorption. This discrepancy may be due to several reasons. Firstly, since expression 1.1 was empirically derived for the case of free space exposure, it did not take into account re-reflections [24]. Secondly, the posture positions of animals in the space relative to the polarization of the exposure affected the final absorption; however, it was also noted in [24; 30] that for \(L/\lambda>>0.4\), the effect of the polarization orientation relative to the object on the SAR is small. Due to the complex geometry of the reflectors in the exposure environment, \"nulls\" and interference extrema can be formed, which also affect the absorption [19; 20; 21; 24; 27; 28]. Depending on the positions of the phantom in such \"hot\" or \"null\" spots, the exposure will increase or decrease, respectively. In the case of distributed absorption, the exposure increased in the model, which was expected due to re-reflections and a higher probability of entering into \"hot\" interference spots. In the numerical modeling, the effect of re-reflection is taken into account and we believe that the difference of 7-10% compared to the theoretical estimate is due to this phenomenon. We do not exclude that re-reflections may contribute more to the SAR, in the case of the increasing exposure power density. However, at a comparatively lower power, assuming the exposure decreases as \(1/r^{2}\), the effects of re-reflection will contribute even less. The development of a generalized SAR estimation technique taking into account the influence of re-reflections requires additional studies based on the statistical analysis of the distribution of elements, animals, and configurations of electromagnetic fields. Studies in this direction are described in [19; 30; 31] and they are still in progress. Great successes have been achieved mainly for the case of completely closed reverberation or anechoic chambers. The paper [30] presents the results of the numerical calculation of SAR for the anatomical model of the Sprague-Dawley rat with 31 tissues in the frequency range of 0.5-5 GHz at EMF power density \(S_{inc}=1\) W/m\({}^{2}\). High-resolution models are mainly important for the study of local volume SAR, and the authors presented both local and whole-body SAR. The whole-body SAR is composed of such local absorptions, where we believe that it is sufficient to use a homogeneous dielectric model instead of a heterogeneous one for qualitative evaluation. At GHz frequencies, waves penetrate less deeply and are reflected more. This is due to the increased conductivity of the skin tissue layer at these frequencies [32; 33]. Conductivity in tissues is in turn related to blood and other substances with high conductivity. Since blood is present in almost the entire volume of the animal, we used a rat phantom with the dielectric parameters of blood. We agree that this approach does not provide true SAR values, but we can compare estimates regarding distributed and non-distributed absorption. A comparison can be made using the example of an estimate for a rat model with L = 24.4 cm and m = 220 g at 2.4 GHz, where whole-body SAR is 0.027 W/kg [30]. This value agrees perfectly with the estimate from expression (1). It is difficult to compare the estimates for the distributed absorption since we know only one work with the concept of radiation with a decreasing incident power density of a group of animals [9]. The \begin{table}
\begin{tabular}{c c c c} \hline
**Group Type** & \(P_{A}\) **[W]** & \(\langle S_{inc}\rangle\) **[W/m\({}^{2}\)]** & \(SAR_{avg}\) **[W/kg]** \\ \hline wbSAR1 & 0.5 & 3.393 & 0.180 (max) \\  & & & 0.0431 (mean) \\  & & & 0.009 (min) \\ \hline wbSAR2 & 0.0891 & 0.605 & 0.0322 (max) \\  & & & 0.0076 (mean) \\  & & & 0.0017 (min) \\ \hline wbSAR3 & 0.0891 & 0.31 & 0.0153 (max) \\  & & & 0.0059 (mean) \\  & & & 0.0022 (min) \\ \hline \end{tabular}
\end{table} 
Table 2: Theoretical SAR Estimation for Experimental Groups.