1 μW-3.75 W Dual-Mode Near/Far-Field Wearable Wireless Power Transfer using a Hybrid Rectenna

While far-field wireless power transfer (WPT) promises a long range of operation, it falls short on the DC power which can be provided. On the other, hand resonant near-field WPT suffers from a short wireless range. In this work, a dualmode high/low-power near/far-field rectenna is demonstrated for the first time based on a flexible rectifier and a textile antenna. Based on a high-efficiency single-series rectifier, the far-field rectenna achieves a peak efficiency of 42.7% from an ultralow power density of 0.43 $\mu \mathrm{W}/\mathrm{c}\mathrm{m}^{2}$, with a 1 V DC output from 4 $\mu \mathrm{W}/\mathrm{c}\mathrm{m}^{2}$. A high-power 6.78 MHz bridge rectifier is designed and implemented on a flexible textile-based substrate with a 10 dB return loss for inputs above 15 dBm. As a near-field receiver, the antenna could receive 3.75 W DC power at 5 cm from the transmitting coil, with an end-to-end efficiency of 30% inclusive of rectifier, coils, and power amplifier losses. Based on the proposed dual-mode antenna, textile-based wearables could be wirelessly powered dynamically using resonant near-field and radiative near-field WPT.