Robust wireless power transfer using a nonlinear parity–time-symmetric circuit

• Published in: Nature (London) Vol. 546; no. 7658; pp. 387 - 390
• Main Authors: Assawaworrarit, Sid, Yu, Xiaofang, Fan, Shanhui
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 15.06.2017; Nature Publishing Group
• Subjects: 639/4077; 639/766/25; 639/766/400; Circuits; Coupling; Efficiency; Electric vehicles; Genetic transformation; Humanities and Social Sciences; Impedance; Lasers; letter; Magnetic resonance; Medical devices; Medical equipment; multidisciplinary; Parity; Phase transitions; Power efficiency; Radiative transfer; Receivers & amplifiers; Robustness; Science; Symmetry; Tuning; Unity; Wireless communications; Wireless power transmission
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature22404

A nonlinear parity–time-symmetric circuit is used to enable robust wireless power transfer to a moving device over a distance of one metre without the need for tuning. Parity time for wireless power A robust, efficient technology for wirelessly charging devices would be a substantial boost for a range of mobile applications including implantable medical devices and electric vehicles. Shanhui Fan and colleagues propose and test a new way of transferring power that doesn't require continual tuning as the distance between source and device is varied, contrary to other approaches. They use the principle of parity–time symmetry, a concept that has been intensively explored in recent years in optical applications by carefully balancing gain and loss, and which has led to new and unusual regimes. Here they apply the principle to electric circuitry, and show how electromagnetic power can be transferred between two metallic plates with an efficiency that is maintained over distances of up to a metre. The work demonstrates a wirelessly powered light-emitting diode (LED) that shines with constant brightness even when its position relative to the power source changes. Considerable progress in wireless power transfer has been made in the realm of non-radiative transfer, which employs magnetic-field coupling in the near field 1 , 2 , 3 , 4 . A combination of circuit resonance and impedance transformation is often used to help to achieve efficient transfer of power over a predetermined distance of about the size of the resonators 3 , 4 . The development of non-radiative wireless power transfer has paved the way towards real-world applications such as wireless powering of implantable medical devices and wireless charging of stationary electric vehicles 1 , 2 , 5 , 6 , 7 , 8 . However, it remains a fundamental challenge to create a wireless power transfer system in which the transfer efficiency is robust against the variation of operating conditions. Here we propose theoretically and demonstrate experimentally that a parity–time-symmetric circuit incorporating a nonlinear gain saturation element provides robust wireless power transfer. Our results show that the transfer efficiency remains near unity over a distance variation of approximately one metre, without the need for any tuning. This is in contrast with conventional methods where high transfer efficiency can only be maintained by constantly tuning the frequency or the internal coupling parameters as the transfer distance or the relative orientation of the source and receiver units is varied. The use of a nonlinear parity–time-symmetric circuit should enable robust wireless power transfer to moving devices or vehicles 9 , 10 .