Wireless Power Transfer: Technology Review, Standardization andHuman Body RF Exposure Assessment
Andrey S. Andrenko
EMC Laboratory, Electromagnetic Standards Research Center
National Institute of Information and Communications Technology
Nukui-Kitamachi 4-2-1, Koganei, Tokyo 184-8795, Japan
Email: andrey@nict.go.jp

Wireless power transfer (WPT) technology has been for a long time envisioned as a game-changing
solution to the problem of wireless supply of electric power. Recently, it has been recognized as one of themost promising means for powering the electric vehicles (EV), IoT wireless devices and wireless sensors
used for healthcare/lifestyle applications. This talk will present the review of modern WPT technology andits historical milestones, discuss the issues of human safety assessment of WPT systems being developed forpractical deployment and latest advances in standardization related to the human safety of EMF radiationfrom the WPT devices. We will begin with the brief description of two main types of WPT systems, namely1) inductive WPT technology as well as its magnetic resonance type operating at 80 kHz to 30 MHz frequency
band where the transmitting and receiving circuits are near-field coupled and 2) radiative (or RF) WPT
systems working at 920 MHz, 2.45 and 5.75 GHz frequencies with the receiving antennas typically being in
the far-field zone of beamforming transmitters. Next, the importance of the human body RF exposure
assessment and human safety compliance of WPT devices necessary for their wide acceptance and practicalcommercialization of WPT technology will be discussed.
According to the ICNIRP guidelines and international standards [1,2], Specific Absorption Rate (SAR)
is a basic restriction in the exposure guidelines while the incident EM strength values are defined as thereference levels. They are used as the metric for assessing the human safety of any EM radiation devices in
the frequency range from 100 kHz to 6 GHz. The necessity of RF dosimetry as the quantification of themagnitude and distribution of absorbed EM energy within biological objects exposed to RF fields will bediscussed. Next, the results of EM simulation of inductive WPT coils operating close to the heterogeneoushuman model and elliptical phantom as a detailed study of the dependency of SAR on the phantom material
properties and size will be presented. An example of measurement E-field assessment of radiative WPT 2.45
GHz system in the near-field and far-field zones of beamforming “retrodirective” transmitter is introduced.
This assessment procedure includes the use of cylindrical phantom to model the human body effect on thesystem performance. The results of elliptical phantom SAR measurements of the radiative WPT systems
operating at 2.45 and 5.75 GHz will also be presented.
Finally, the latest developments of the IEC activities on the international standardization of the assessment
methods of the human exposure to EM fields from inductive WPT systems (frequency range from 1kHz to30 MHz) and from radiative WPT systems (frequency range from 30 MHz to 300 GHz) will be presented.
The new trends of the WPT technology and challenges to its world-wide applications will also be discussed.
Acknowledgement
This work has been supported by the Ministry of Internal Affairs and Communications of Japan Grant
Number JPMI10001.
References
1. ICNIRP. “Guidelines for limiting exposure to electromagnetic fields (100 kHz to 300 GHz)”. HealthPhys. 118(5):483–524; 2020.
2. IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency ElectromagneticFields, 3 kHz to 300 GHz, IEEE Standards Dept., New York, USA, C95.1, 2005.