Efficient NFC coil antennas for fully enclosed metallic‐framed wearable devices. Issue 3 (18th December 2019)

• Record Type: Journal Article
• Authors: Choi, Jaehyun; Lim, Sangho; Hong, Wonbin
• Is Part Of: IET microwaves, antennas & propagation. Volume 14:Issue 3(2020)
• Page Start: 211
• Page End: 214
• Publication Date: 2019-12-18
• Subjects: mobile handsets -- coils -- radiofrequency identification -- antennas -- near‐field communication; out‐of‐phase current amplitude -- asymmetric coil topology -- 13.56 MHz NFC applications -- presented techniques -- metallic frame -- NFC forum certification -- drive current -- NFC circuitry -- efficient NFC coil antennas -- metallic‐framed wearable devices -- near‐field communication -- fully enclosed metallic‐frames -- short‐circuit passages -- metallic‐frame -- frequency 13.56 MHz; Microwaves -- Periodicals; Microwave antennas -- Periodicals; Antennas (Electronics) -- Periodicals; Radio wave propagation -- Periodicals; Microwave communication systems -- Periodicals; 621.381305
• DOI: 10.1049/iet-map.2019.0451
• Languages: English
• ISSNs: 1751-8725

Abstract

Abstract : This study reports methods of alleviating the effect on inductive near‐field communication (NFC) coils caused by fully enclosed metallic‐frames for wearable devices such as smartwatches. Two techniques that, respectively, involve creating two short‐circuit passages to modify the distribution of the out‐of‐phase current on the metallic‐frame and reducing the out‐of‐phase current amplitude by devising an asymmetric coil topology is presented and studied in detail. Extensive simulation, prototyping and measurement are carried out for 13.56 MHz NFC applications. The presented techniques can, respectively, improve the induced magnetic coupling by 43 and 30% under identical conditions in the presence of the metallic frame. Furthermore, both methods comply with the NFC forum certification and do not require the need to increase the drive current and power consumption of the NFC circuitry.