Comparison and Limitations of Measurement Techniques forBody Absorption in mm-Waves : Project report

Wireless communications are rapidly evolving. In particular, users are demanding new services in the present networks that require higher data transfer. The new generation of mobile communications, 5G, started to be deployed at the end of 2019. However, this first implementation of 5G will only cover part of the needs of users. Further research to increase the rates of wireless communications is currently needed to cover the expectations in the near future. Since most of the low frequency spectrum is already crowded, the only possibility is increasing the operational frequency to the millimetre-wave (mm-wave) regime where narrow bands permit largerdata transfer and short delays. As all the devices radiating radio frequency electromagnetic fields (EMFs), the mm-wave devices need to be assessed to show the compliance with EMF exposure limits specified by standards and regulations. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) is an international association whose EMF guidelines from 1998 have been adopted in standards and regulations in many countries worldwide. On March 11, 2020, ICNIRP released new guidelines for exposure to RF EMF in the frequency range 100 kHz to 300 GHz. One difference between the new and the previous guidelines from 1998 is the basic restrictions on the whole-body exposure. The whole-body exposure basic restriction in ICNIRP (1998) was set in terms of the quantity “SAR” (Specific Absorption Rate). This is also the case for ICNIRP (2020). However, whereas this restriction only applied upto 10 GHz in ICNIRP (1998), it is applicable across the entire 100 kHz to 300 GHz range in ICNIRP (2020). This will ensure that exposures from new technologies donot lead to an excessive temperature rise deep in the body. The whole-body averaged SAR is defined as the total absorbed power divided by the whole-body mass. For frequencies below 10 GHz, the whole-body SAR measurement procedure explained in EMF exposure assessment standards requires measuring the field strength inside a tissue-equivalent liquid (a human phantom) to obtainthe total absorbed power. However, this method is very difficult to use for high frequency EMF waves (such as mm-waves) since the penetration depth is superficial. Within this project, we study alternatives for measuring the whole-body averaged SAR at mm-waves. In this report, we outline various methods for estimating the SAR reported in the literature. From this literature review, we identify promising techniques. We provide a critical assessment of two of the promising techniquesusing numerical simulations.QC 20221213