Magnetically Coupled Resonance Wireless Power Transfer (MR-WPT) with Multiple Self-Resonators

Wireless power transfer (WPT) has been studied formore than one hundred years sinceNikola Tesla proposed his WPT concept. Asmore and more portable electronic devices and consumer electronics are developed and used, the need for WPT technology will continue to grow. Recently, WPT via strongly coupled magnetic resonances in the near field has been reported by Kurs et al. (2007). The basic principle of WPT based on magnetically coupled resonance (MR-WPT) is that two self-resonators that have the same resonant frequency can transfer energy efficiently over midrange distances. It was also reported that MR-WPT has several valuable advantages, such as efficient midrange power transfer, non-radiative, and nearly omnidirectional. It is certain that these properties will help to improve the performance of current wireless power transfer systems and be utilized well for various wireless power transfer applications such as electric vehicles, consumer electronics, smart mobile devices, biomedical implants, robots, and so on. Up to now, several important articles have been published. Karalis et al. (2008) reported detailed physical phenomena of efficient wireless non-radiative mid-range energy transfer. Sample et al. (2010) reported an equivalent model and analysis of an MR-WPT system using circuit theory, and Hamam et al. (2009) introduced an MR-WPT system that used an intermediate self-resonator coil to extend the coverage of wireless power transfer that is coaxially arranged with both Tx and Rx self-resonant coils. In Figure 1, a practical application model of wireless power charging of multiple portable electronic devices using MR-WPT technology is illustrated. Multiple devices are placed on the Rx self-resonator, which is built into the desk, and the Tx self-resonator is built into the power plate wall. The Tx self-resonator is strongly coupled with the Rx one and then both Tx and Rx self-resonators transfer energy efficiently even though the Tx self-resonator is geometrically perpendicular to the Rx self-resonator. In order to create this system, it is necessary to characterize power transfer efficiency and especially mutual inductance of the MR-WPT system with two self-resonators arranged perpendicularly. However, there have been few research reports published that analyze the characteristics of MR-WPT regarding a geometrical arrangement between Tx and Rx self-resonators and between Tx or Rx and intermediate self-resonators. In this article, the characteristics of wireless power transfer between two self-resonators arranged in off-axis positions are reported and the power transfer efficiency of an MR-WPT 3