5G Electromagnetic Field Exposure at 26 GHz: Absorbed Power Density Assessment

This article investigates the absorbed power density (APD) for a 26 GHz coaxial feed microstrip antenna with a partial ground, utilizing Rogers RT/Duroid 5880 substrate. The microstrip antenna with a dimension of 10.8 mm × 10.8 mm demonstrates excellent performances in terms of reflection coefficient, realized gain, and efficiency with values of −41.55 dB, 8.2 dBi, and 97%, respectively. The APD is assessed by determining the power density on the curve probe lines through a three-layered human head phantom, that consists of skin, fat, and muscle. The head phantom is constructed using CST voxel family data of an eight-week-old female infant and a 4-cole-cole dispersion model. In the APD assessment, the antenna is excited by 6.99 dBm (5 mW) and placed 5 mm from the phantom, and 17 curve probe lines that extend 20 mm in a perpendicular direction from the antenna, are adopted to cover the $4\ \text{cm}^{2}$ averaging area of the phantom. The APD of $2.09\ \mathrm{W}/\mathrm{m}^{2}$ averaged over $4\ \text{cm}^{2}$ exposure area is obtained, which complies with the standardized limit. The proposed APD assessment method could serve as an alternative to mathematical modeling or laboratory measurement. CST Microwave Studio (MWS) is utilized for carrying out all the design and analyses.

I. Introduction

The emerging fifth-generation (5G) networks are incorporating millimeter-wave (mm-Wave) spectrums to accelerate data transfer rates, specifically at frequencies higher than 24 GHz [1] [2]. Consequently, concerns over the probable health implications of electromagnetic radiation at these higher frequencies have been brought up by this allocation of frequencies. Therefore, an organization including the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and IEEE International Committee on Electromagnetic Safety have released regulations regarding these issues. In the updated safety parameters, a distinct dosimetry volume, referred to as epithelial power density in the IEEE standard or absorbed power density (APD) in the ICNIRP guidelines, has been employed as the fundamental constraint in the frequency range of 6 to 300 GHz. The APD criteria require an average over a area of the bodily region for localized exposure scenarios with a frequency less than 30 GHz. The allowable standard APD limit on the averaging area is [1]. The APD level depends on numerous parameters including the operating frequency, antenna excitation power, and the distance of the exposure from the antenna. It indicates that the antenna excitation power is very crucial because the usage of high excitation power leads to an increase in the APD level [3]. Therefore, this article presents a simulation technique to estimate the APD level in human head tissues due to the electromagnetic field (EMF) radiation from a 5G antenna operating at the frequency of 26 GHz. Figure 1.

Proposed patch antenna design at (a) top view of the patch and (b) bottom of the ground plane