Battery-Free Wireless Node Powered using High-Efficiency Harvesting of 900 MHz GFSK-Modulated Packets with a Compact Rectenna

Radio Frequency (RF) Simultaneous Wireless Information and Power Transfer (SWIPT) has attracted significant interest with a range of SWIPT-specific rectenna implementations. However, the impact of modulated waveforms on a capacitor charging time remains unknown, and a system powered off packets us yet to be demonstrated. This paper presents an RF-powered sub-1 GHz sensor node through modulated packages with a sub-0 dBm sensitivity without any DC-DC power management circuitry. Using Gaussian Frequency Shift Keying (GFSK) modulated signals from a commercial IoT transceiver, the RF-DC power conversion efficiency (PCE) is investigated for both a resistive and capacitive load. It is shown that GFSK modulation with varying data rates has minimal influence on the PCE. A miniaturized rectenna is demonstrated charging a supercapacitor powering a sub-1 GHz sensor node for over 32 s, charged using 40 GFSK packets transmitted in 62 s, at 1.6 m from a 4 W circularly-polarized source at 900 MHz. The demonstrated rectenna exhibits over an order of magnitude improvement in the sensitivity over previous works harvesting modulated packets.