Optimization and Analysis of Multilayer Planar Spiral Coils for the Application of Magnetic Resonance Wireless Power Transfer to Wearable Devices

Young-Jin Park, Ji-Eun Kim, Kyung-Min Na, Ki-Dong Yang and Kyung-Hwan Cho
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Young-Jin Park: Korea Electrotechnology Research Institute, An-San 15588, Korea
Ji-Eun Kim: Korea Electrotechnology Research Institute, An-San 15588, Korea
Kyung-Min Na: Eta Electronics R&D, Gangnam-gu, Seoul 06121, Korea
Ki-Dong Yang: Korea Electrotechnology Research Institute, An-San 15588, Korea
Kyung-Hwan Cho: Korea Electrotechnology Research Institute, An-San 15588, Korea

Energies, 2021, vol. 14, issue 16, 1-19

Abstract: In this study, small multilayer planar spiral coils were analyzed and optimized to wirelessly charge an in-ear wearable bio-signal monitoring device in a wine-glass-shaped transmitter (Tx) based on magnetic resonance wireless power transfer (MR-WPT). For analysis of these coils, a volume filament model (VFM) was used, and an equivalent circuit formulation for the VFM was proposed. The proposed method was applied to design effective multilayer coils with a diameter and height of 6 and 3.8 mm, respectively, in the wearable device. For the coils, a printed circuit board having a 0.6 mm thick dielectric substrate and a 2 oz thick copper metal was used. Moreover, the coils on each layer were connected in series. The dimensions of the double-, four-, and eight-layer coils were optimized for the maximum quality factor (Q-factor) and coupling efficiency. The operating frequency was 6.78 MHz. The optimal dimensions for the maximum Q-factor varied depending on the number of coil layers, pattern width, and turn number. For verification, the designed coils were fabricated and measured. For the four-layer coil, the coupling efficiency and Q-factor using the measured resistance and mutual inductance were 58.1% and 32.19, respectively. Calculations showed that the maximum Q-factor for the four-layer coil was 40.8 and the maximum coupling efficiency was 60.1%. The calculations and measurement were in good agreement. Finally, the entire system of the in-ear wearable bio-signal monitoring device, comprising a wine-glass-shaped transmitter, the designed receiving coil, and a monitoring circuit, was fabricated. The measured dc-dc efficiency of the MR-WPT system was 16.08%.

Keywords: magnetic resonance wireless power transfer (MR-WPT); planar spiral coil; volume filament model (VFM); wearable devices; planar multilayer coil (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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