Use of Frequency-Selective Surface for Suppressing Radio-Frequency Interference from Wireless Charging Pads

Wireless charging is an emerging technology that involves multidisciplinary research. Power converters driving the planar wireless charging pads generate radio-frequency interference (RFI) that can degrade the signal transmission and reception of portable communication devices such as mobile phones. In this paper, the practical evidence of the RFI arising from the switching electronics in a wireless charging pad is provided and the use of a frequency-selective surface (FSS) is proposed for reducing the RFI. The basic principle of using the FSS design, previously used for stealth applications, is explained and practically verified for suppressing the RFI in wireless charging pads. The FSS structures show good RFI blocking performance with negligible effect on the charging energy efficiency. Practical tests have confirmed that the maximum sensitivity of the phone can be improved by 6.5-8.4 dB in GSM900 and by 2.3-6.3 dB in GSM850 when a double-sided FSS is employed. Moreover, the total isotropic sensitivity is improved by 3.3-5.6 dB in GSM900 and 0.2-3.3 dB in GSM850. The proposed FSS can become a low-cost accessory to the wireless charging pads for portable electronics.