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Sensors 2017, 17(6), 1358; doi:10.3390/s17061358

An NFC on Two-Coil WPT Link for Implantable Biomedical Sensors under Ultra-Weak Coupling

Institute of Application Specific Instruction-Set Processors, Beijing Institute of Technology, 5 South Zhongguancun Street, Haidian District, Beijing 100081, China
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Received: 5 April 2017 / Revised: 26 May 2017 / Accepted: 7 June 2017 / Published: 11 June 2017
(This article belongs to the Special Issue Biomedical Sensors and Systems 2017)

Abstract

The inductive link is widely used in implantable biomedical sensor systems to achieve near-field communication (NFC) and wireless power transfer (WPT). However, it is tough to achieve reliable NFC on an inductive WPT link when the coupling coefficient is ultra-low (0.01 typically), since the NFC signal (especially for the uplink from the in-body part to the out-body part) could be too weak to be detected. Traditional load shift keying (LSK) requires strong coupling to pass the load modulation information to the power source. Instead of using LSK, we propose a dual-carrier NFC scheme for the weak-coupled inductive link; using binary phase shift keying (BPSK) modulation, its downlink data are modulated on the power carrier (2 MHz), while its uplink data are modulated on another carrier (125 kHz). The two carriers are transferred through the same coil pair. To overcome the strong interference of the power carrier, dedicated circuits are introduced. In addition, to minimize the power transfer efficiency decrease caused by adding NFC, we optimize the inductive link circuit parameters and approach the receiver sensitivity limit. In the prototype experiments, even though the coupling coefficient is as low as 0.008, the in-body transmitter costs only 0.61 mW power carrying 10 kbps of data, and achieves a 1 × 10 - 7 bit error rate under the strong interference of WPT. This dual-carrier NFC scheme could be useful for small-sized implantable biomedical sensor applications. View Full-Text
Keywords: biomedical telemetry; near-field communication; wireless power transmission; inductive link; implantable biomedical sensors biomedical telemetry; near-field communication; wireless power transmission; inductive link; implantable biomedical sensors
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Gong, C.; Liu, D.; Miao, Z.; Wang, W.; Li, M. An NFC on Two-Coil WPT Link for Implantable Biomedical Sensors under Ultra-Weak Coupling. Sensors 2017, 17, 1358.

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