Evaluation of nonuniform field exposures with coupling factors

Tetsu Sunohara, Akimasa Hirata, Ilkka Laakso, Valerio De Santis, Teruo Onishi

Research output: Contribution to journalArticleScientificpeer-review

19 Citations (Scopus)


In this study, the safety compliance for nonuniform field exposures is discussed using coupling factor concepts. The coupling factor, which is defined in the International Electrotechnical Commission 62311 standard, is extended to consider the effects of harmonics and also to apply to the specific absorption rate (for frequencies up to 30 MHz). The proposed compliance procedure is applied to and demonstrated for a prototype wireless power transfer (WPT) system with induction coupling operating at the fundamental frequency in 140 kHz band. First, measurements confirm that the perturbation of the external magnetic field strength and S11 parameter of a one-loop antenna by a human-equivalent phantom are sufficiently small, suggesting the applicability of the magneto-quasi-static approximation to frequencies up to 30 MHz. Then, the frequency characteristics of the coupling factor are derived for the WPT system. For the prototype system that is not optimized for commercial usage, the maximum allowable transmitting power is relaxed by a factor of 23 with the proposed procedure. The contribution of the harmonics decreased the allowable transmitting power by 39%, indicating their importance for safety compliance.

Original languageEnglish
Pages (from-to)8129-8140
Number of pages12
JournalPhysics in Medicine and Biology
Issue number20
Publication statusPublished - 6 Oct 2015
MoE publication typeA1 Journal article-refereed


  • harmonics
  • intermediate frequency band
  • radiation dosimetry
  • safety evaluation
  • wireless power transfer

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