# Estimation of SAR Average in Rats during 5G NR Chronic Exposure
###### Abstract
A quarterwave monopole inside a room covered with aluminum was used as the source. Twenty animal cages, each containing five unrestrained animals oriented parallel to the long axis of the antenna, were mounted on the wall perpendicular to the ground plane in a circular array at a radius of 650 mm around the antenna. The room was reflective, resulting in an undefined standing wave pattern, and the animals were allowed to move freely in the cage as well as to converge. In the cages' area, the incident power density values varied from 2.6 to 13 W/m\({}^{2}\). The whole-body SAR estimations were provided by measuring the internal EMF components of the mice phantom per 1 W/m\({}^{2}\), which were then recalculated to the actual power density. Measurements of the EMF fields induced by RF fields were made on three phantoms representing small, medium, and large mice in a semi-anechoic room. In [10; 11], the authors present the design features and technical implementation of radiofrequency irradiation systems developed for the National Toxicology Program (NTP). The reverberation chambers were characterized in terms of the homogeneity of the electromagnetic field inside the chambers. SAR was evaluated using the thermometric method on phantoms. More recent studies related to fifth-generation cellular technologies are also known. The range of available frequencies for the implementation of 5G NR modulation, which is defined in Tables 5.2-1 and 5.2-2 of 3 GPP TS38.104 [12], varies from 410 MHz to 7125 MHz (FR1) and 24,250 MHz to 52,600 MHz (FR2). Different frequencies are used in different regions. In [13; 14], the effect of 5G signals with a frequency of 3.5 GHz on living human cells' keratinocytes and fibroblasts was investigated. The SAR was assessed by the thermometric method [14]. In study [15], the authors investigated the effects of 4.9 GHz (one of the work ing frequencies of 5G communication) radiofrequency (RF) field on emotional behaviors and spatial memory in adult male mice. Mice were exposed to 4.9 GHz radiofrequency radiation for 21 days, at 1 h/day. The power density (PD) was 50 W/m\({}^{2}\) and the distance from the radiation antenna to the target animals was 70 cm. SAR measurements were not provided. A wide review was presented in [16] for frequencies 6-100 GHz. The authors analyzed 94 relevant publications performing in vivo or in vitro investigations. In addition to biological studies, various techniques for SAR estimation are being developed, in particular using numerical methods [17; 18; 19]. In [19], the authors adopted the Poggio-Miller-Chang-Harrington-Wu-Tsai formulation of the method of moments to directly determine the specific absorption rate (SAR) of differently shaped dielectric phantoms placed in an RC and demonstrated its validity via comparing the numerical temperature rise with those obtained from experiments. Resonant absorption studies, based on the antenna theory [20; 21], are also known. Analyzing approaches to animal experimentation from the available literature, it can be seen that they may be conceptually different. Obviously, one or another experimental design is justified by the researchers. Based on the overall concept of the experiment and the available resources, a certain methodology is used. This paper considers the problem of SAR estimation in an experiment [22], which conceptually differs significantly from the majority of works. For long-term experiments to study the physiological reactions of animals, 24 h irradiation of free-behaving animals in natural laboratory conditions is required. In other words, animals need to be kept with minimal interference in their \"domestic\" life to eliminate stress factors. A similar concept was in study [9]. Under such conditions, an objective estimate of the SAR can be quantified at the maximum and minimum limits. It is also necessary to set exposure regimes to avoid increasing the temperature of exposed animals and to ensure safe levels for laboratory personnel.