# Estimation of SAR Average in Rats during 5G NR Chronic Exposure
###### Abstract  
To study physiological reactions in the brain and skin of higher mammals exposed to chronic radiofrequency radiation, specific absorption ratio (SAR) determination is required and time-consuming numerical methods are used. The paper deals with the estimation of the whole-body specific absorption rate (SAR) in rats chronically exposed to external electromagnetic fields, as well as the development of a laboratory setup simulating the operation of a fifth-generation 5G New Radio base station (with a signal bandwidth of 15 MHz and a carrier frequency of 2.4 GHz). The paper presents a modified method for theoretical SAR estimation for one-sided irradiation and distributed absorption. Mean whole-body SAR values were estimated by the proposed method and numerically modeled with the CST Microwave Studio simulation software 2020 package using primitive rat models. Dielectric parameters in the numerical simulation were used from the software library. The IEEE/IEC 62704-1 algorithm was used to investigate SAR in numerical simulations. The theoretical estimates and numerical simulations were compared for different SAR distributions and were found to be qualitatively comparable. The differences between approximate theoretical estimates and numerical simulations are 7% and 10% for distributed and non-distributed absorptions, respectively. The proposed method, which takes into account the decreasing power flux density, can be used to estimate the approximate whole-body SAR during chronic electromagnetic field exposure in rats. dosimetry; whole-body SAR; 5G NR; rats +
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absorption of incident EM energy and the distribution of the absorbed exposure energy in rats. To date, there are several international documents on recommendations for limiting both short-term and long-term, continuous and intermittent radio frequency (RF) EM exposures. These recommendations are based on thorough scientific assessments. The main sources of such documents are the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the Institute of Electrical and Electronics Engineers (IEEE) [1; 2; 3]. The key values used as quantitative limits on the EMF effects on a person are the power density and the specific absorption rate (SAR). SAR characterizes the amount of electromagnetic energy absorbed per unit mass. Pursuant to ICNIRP and IEEE documents, a value to be used depends on EMF frequencies and exposure subjects. The Russian Federation establishes sanitary rules and regulations estimating the maximum permissible EMF values by the power density in the frequency range from 300 MHz to 300 GHz [4]. Thus, determination of these values is important when conducting studies of EMF effects on living organisms or their phantoms. Depending on the conditions of experiments with animals and the irradiation procedure, SAR estimation can be performed in different ways. Even before the coming of 5G technologies, there are many known studies related to SAR estimation. There are many studies on the development of single anechoic chambers [5]. The authors paid attention to the influence of the field inhomogeneity obtained in the presence of the cell, which was found to be not significant in the SAR estimation. SAR was determined using calorimetric and thermographic methods. The authors of [6; 7] developed the Radial Electromagnetic Cavity, which is optimized for irradiation of the whole body of mice in vivo with 900 MHz radiofrequency fields. In [8], an exposure setup with up to 30 rats at the bottom of an anechoic chamber was utilized. 900 MHz plane-wave microwaves were emitted from a horn antenna located 600 mm above the animals. All animals were located individually in plastic cages small enough to align them in the direction of the long axis parallel to the electric field. SAR was estimated on gel-based phantoms using a temperature change measurement technique. A notable work, in terms of the radiating setup, is presented in the study [9]. The authors exposed 100 mice to a modulated 900 MHz field.