A Frequency-Selective EMI Reduction Method for Tightly Coupled Wireless Power Transfer Systems using Resonant Frequency Control of a Shielding Coil in Smartphone Application


Current wireless power transfer (WPT) technology is widely used for various applications because of convenience and safety. However, WPT systems have problems with electromagnetic field (EMF) leakage, which can cause electromagnetic interference (EMI) issues for nearby electrical devices at various frequency ranges. In the case of the Qi standard that operates from 105 to 205 kHz frequency range, the third or fifth harmonic can cause EMI problems for the amplitude modulation bands of a radio corresponding from 530 to 1700 kHz. For the first time, in this article, we propose a frequency-selective EMI reduction method with an additional shielding coil for the effective suppression of EMI radiation of a WPT system. The proposed method reduces the EMI in a specific frequency range and has insignificant effect on the power transfer efficiency (PTE). We experimentally verified that the proposed method with the shielding coil reduced the EMF leakage by 8.96 dB of the third harmonics without reduction of the PTE. Furthermore, we mathematically designed the shielding coil using the proposed method. The mathematical calculation based on the equivalent circuit models is strongly correlated with the experimental measurement results.


Electrical and Computer Engineering

Research Center/Lab(s)

Electromagnetic Compatibility (EMC) Laboratory


This work was supported in part by Basic Science Research Program funded by the Ministry of SMEs and Startups under Grant S2604684, in part by “Development of Interconnection System and Process for Flexible Three-Dimensional Heterogeneous Devices” funded by the Ministry of Trade, Industry and Energy in Korea, and in part by the Ministry of Science, ICT and Future Planning, South Korea, under the Information Technology Research Center Support Program under Grant IITP-2018-2016-0-00291 supervised by the Institute for Information & Communications Technology Promotion.

Keywords and Phrases

Electromagnetic Fields (EMFs); Electromagnetic Interference (EMI); Harmonics; Shielding Coil; Wireless Power Transfer (WPT)

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Document Type

Article - Journal

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© 2019 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Dec 2019