Annals of Telecommunications

, Volume 74, Issue 1–2, pp 53–65 | Cite as

A new extrapolation expression for exposure evaluation inside a human-equivalent liquid phantom in the vicinity of wireless power transfer systems

  • Satoshi Shimoyama
  • Jerdvisanop ChakarothaiEmail author
  • Kanako Wake
  • Takuji Arima
  • Soichi Watanabe
  • Toru Uno


To ensure human safety against electromagnetic exposures from wireless power transfer (WPT) systems operating at MHz-band frequencies, a compliance test must be conducted using either numerical simulations or measurements. In practice, measurements of the specific absorption rate (SAR) inside a human-equivalent liquid phantom are required for exposure evaluation. However, accurate measurements of SAR are difficult, especially at a location close to the phantom boundary, owing to the boundary effect, caused by the field disturbance due to the SAR probe itself. Hence, it is necessary to use an extrapolation method to determine the internal electric field or SAR. In this study, we propose a new extrapolation expression based on the characteristic of electromagnetic fields inside the phantom in order to estimate internal electric field strength or SAR. The validity of the proposed expression was demonstrated both numerically and experimentally. From the results, we confirmed that the difference in the internal electric field strength inside a liquid phantom was less than 3% between our proposed extrapolation expression and the method of moments (MoM). For SAR measurements using two types of actual WPT systems, i.e., solenoid and flat-spiral types, we found that the proposed expression can be used to evaluate the spatial peak 10-g average SAR with a difference of less than 30% compared with those numerically obtained by MoM.


Compliance test Exposure evaluation Extrapolation method Specific absorption rate Wireless power transfer systems 


Funding information

This study was financially supported by the Ministry of Internal Affairs and Communications, Japan.


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Copyright information

© Institut Mines-Télécom and Springer Nature Switzerland AG 2018

Authors and Affiliations

  • Satoshi Shimoyama
    • 1
    • 2
  • Jerdvisanop Chakarothai
    • 1
    Email author
  • Kanako Wake
    • 1
  • Takuji Arima
    • 1
    • 2
  • Soichi Watanabe
    • 1
  • Toru Uno
    • 2
  1. 1.National Institute of Information and Communications TechnologyTokyoJapan
  2. 2.Tokyo University of Agriculture and TechnologyTokyoJapan

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