# Estimation of SAR Average in Rats during 5G NR Chronic Exposure
## 2 Materials and Methods  
### Experimental Procedure  
The Adalm pluto SDR (software-defined radio) active learning module is used as a source for generating 5G NR signals. A downlink frequency range signal FR1 was used--from a base station to a user. The signal was produced using a software package for generating test signals of the 5G NR standard, developed under agreement No. 075-11-2019-031 with the Ministry of Science and Higher Education of the Russian Federation, dated 26 November 2019. The bandwidth of the generated signal is 15 MHz and the carrier frequency is 2.4 GHz. The signal spectrum is shown in Figure 1.  
The 2.4 GHz frequency is chosen for several reasons. First, this frequency is defined in Table 5.2-1 of 3 GPP TS38.104 [12]. Secondly, the ratio of the wavelength at this frequency to the animal length is different from 1, which avoids the possible temperature rise caused by the resonant absorption described in [21; 23; 24]. In the third, this range is already widely used in WiFi technologies, which allows us to generalize the research to some extent. Also, this band has performed well in terms of coverage distance, compared to higher frequencies.  
To amplify the signal, a blm9D2324-25b amplifying module was used with a gain of 28 dB in a given frequency range. A PlastRam antenna, developed at TSU Department of Radiophysics, was used as a radiating unit with dimensions 240 \(\times\) 168 mm. The combined linear polarization antenna has one feed port with an impedance of 50 Ohm and is an electric and magnetic dipole with a combined phase center.  
Figure 2 shows the radiation pattern (RP) of the antenna at a frequency of 2.4 GHz. The RP has two symmetrical lobes, which enables uniform whole-body exposures of two rats. The antenna gain is 7 dBi. For the combined antenna applied, electrical and magnetic energy are considered to become balanced at distances longer than a wavelength (12.5 cm).  
Figure 3 shows a schematic for an experimental setup designed to study the exposure effects of a 5G NR base station. A radiating unit consisting of a network device, a cascade amplifier, and an antenna is powered from an external source and exposes the cages (Techniplast) from one side. A shield (with dimensions of 98 \(\times\) 25 cm) is placed on the other side, to limit any possible exposure from the outside.  
Figure 1: Zero-frequency Signal Spectrum.  
Figure 2: Free Antenna Pattern and characteristics.  
The signal power supplied to the antenna was 0.5 W and 0.0891 W for various exposure cases. The choice of these levels is related to ensuring that the SAR does not exceed the ICNIRP restrictions for whole-body SAR. The power was measured with an M3M-18 microwave power meter (Micran).  
All animals were treated in accordance with the EU Council Directive of 24 November 1986 (86/609/EEC) and were approved by the Animal Research Ethics Committee of Tomsk State University.  
Three dose groups of male Wistar rats were used in experiment. The first and second groups of experimental animals included 10 rats (5 per cage) with an average weight of 488 g and a length of 25 cm. The first group was exposed to 24 h radiation for a week with an average dose of 3.393 W/m\({}^{2}\). The antenna was placed 12 cm away from the cages.  
The second group was exposed to 24 h EMF radiation for 4 weeks with a dose of 0.605 W/m\({}^{2}\). The third group included 20 young rats (10 per cage) with an average weight of 295 g and a length of 20 cm. The antenna was placed 20 cm away from the cages. To equalize the average SAR, the third group was exposed to a lower average dose (0.31 W/m\({}^{2}\)).  
Figure 4 shows that the rats could roam freely within their individual cages, thereby receiving different electromagnetic doses. In this exposure configuration, the absorption in the cage becomes spatially distributed.  
Figure 4: Laboratory setups.  
Figure 3: Experimental design.