Time-varying systems to improve the efficiency of wireless power transfer

Conventional wireless-power-transfer (WPT) systems are linear and time invariant, which sets fundamental limitations on their performance, including a trade-off between transfer efficiency and the level of transferred power. In this paper, we introduce and study a possibility of temporal modulation for inductive wireless-power-transfer systems and uncover that this trade-off is avoided as a consequence of varying the inductive coupling strength in time. Our theoretical analysis reveals that under the optimal modulation depth and phase, the time modulation can yield a substantial improvement in the WPT efficiency, while the received power at the load is also improved compared to the static WPT reference system. We experimentally demonstrate the concept with a low-frequency system and observe a threefold improvement in efficiency over the reference static counterpart. This technical capability reconciles the inherent trade-off between the WPT efficiency and transferred power, paving the way for simultaneous advancements in both efficiency and delivered power.