Analysis of a Near Field Communication wireless power system

Near Field Communication (NFC) readers, ubiquitously embedded in smart-phones, buses and other infrastructures, are able to wirelessly deliver mW-level power to ultra-low power, passive NFC tags via a coupled magnetic field. Additionally, an NFC reader can leverage the coupled communication channel to support relatively heavy computational applications, such as sensing, visual displays, etc. Consequently, reliable and efficient power-transfer with robust communication in the cm reading range is required to enable various more demanding NFC-WISP applications. However, there is a fundamental tradeoff between wireless power delivery and resonator bandwidth, which are critical to NFC communication. Another common trait of magnetically coupled systems is the vulnerability to variations in tag reading distance and antenna misalignment. To mitigate these challenges, we present two simulation-based investigations to study the power transfer and bandwidth performance given different NFC reading range with consideration of parasitic effects. Firstly, we compare a 2-coil NFC system with a 3-coil NFC system via theoretical analysis utilizing a simplified simulation model by ignoring the cross-coupling effect. Secondly, we present the influence of cross-coupling effects of a 3-coil system using a complex model. Finally, we demonstrate the effect of parasitic capacitance across coils for both 2 and 3-coil systems.