SAR evaluation in models of an adult and a child for magnetic field from wireless power transfer systems at 6.78 MHz

Abstract

One of the promising applications for wireless power transfer (WPT) systems is to charge consumer electronics devices. Resonant-type wireless chargers operate at the frequency of 6.78 MHz and may be mounted inside office desks and table tops. In this frequency band, the specific absorption rate (SAR) averaged over 10 g of tissue is an essential factor to be evaluated for human protection from radio-frequency near-field exposure. Detailed analysis of a peak value of 10 g averaged SAR for WPT system with multiple receivers has not been conducted so far. In this study, we compare the peak values of 10 g averaged SAR for the magnetic field leaked from WPT systems with a transmitting coil coupled with a single- or double receiving coil. From computational results, we observed a marginal enhancement of the SAR for the exposure scenario with double-receiving coils. The SAR in the child was smaller than that in the adult because of the difference in the magnetic flux density passing through the human body model. When comparing the SARs in the standing and sitting postures, the former SAR was observed to be 20–30% greater than the latter.