Metamaterial-Controlled Parity-Time Symmetry in Non-Hermitian Wireless Power Transfer Systems

Wireless power transfer (WPT) technologies contain two main categories, radiative and non-radiative. Non-radiative WPT utilizes the magnetic near-field to carry energy and is more commonly used due to its advantages of high-power volume and safety. The receiving (Rx) resonator couples with the transmitting (Tx) resonator through magnetic mutual induction. Inductive WPT systems can be described as non-Hermitian systems through coupled-mode theory. Power transfer in such systems is efficient when forming PT-symmetric states, which could be guaranteed by the physical symmetry in a strong coupling regime. However, spontaneous symmetry breaking happens in the weak coupling regime as the increasing of the Tx-Rx separation, where the resonant states become anti-PT-symmetric.<br/><br/>Relay resonators can be used to increase the overall coupling and, therefore, increase the maximum Tx-Rx separation for the PT-symmetric state. The PT-symmetric states in such systems are also known as the topological edge state for magneto-inductive waves, which have been used for mid-range WPT and frequency-robust WPT. However, one drawback of the relay resonators is the potential involvement of higher order resonant states of the system; many of the states are anti-PT symmetric. To avoid these states, spatial arrangement of the relay resonators needs to be symmetric and the geometry of the Tx and Rx resonators need to be identical. Such requirements are impractical in many applications, such as free-positioning WPT.<br/><br/>Metamaterials, demonstrating excellent ability in manipulating electromagnetic and acoustic fields and waves, show great potential in solving this challenge. Researchers have developed metamaterials to control the PT-symmetry for above-unity transmission and reflection, nanoscale sensing, and coherent perfect absorption. However, such an approach remains challenging for WPT systems due to the lack of accurate control in the metamaterial’s resonance mode. In our previous works, we have demonstrated a quasi-Hermitian metamaterial that can achieve on-demand field-shaping for magnetic resonance imaging and WPT. In this conference presentation, we will extend the theory by showing metamaterial-controlled PT-symmetry in a non-Hermitian WPT system.<br/><br/>We derive the states of the system and show that a PT-symmetric state can be achieved with certain metamaterial’s configuration. The sizes of the Tx and Rx do not need to be identical, and their physical positions are not limited as long as operating in the strong coupling regime. We prove that the state is stable when the system operates in a strong coupling regime. We theoretically and experimentally demonstrate the transition between anti-PT-symmetric and PT-symmetric states controlled by the metamaterial’s configuration. We further show that the PT-symmetric state can be achieved with different spatial arrangements of the Rx resonator. This technique largely increases physical freedom of Tx and Rx and provides a paradigm for designing many-body WPT systems.