RF Energy Harvester with Constant Off-Time Charger for Batteryless Devices

Traditional batteryless radio frequency energy harvesting systems are promising for realizing low-cost Internet of Things devices. However, due to variations in the received power, such systems suffer from unpredictable charging time, which can be critical for multi-node communication or in controlling the system's throughput. This paper presents a batteryless RF energy harvester that provides a predictable charging time which is resilient to changes in input RF power, improving system uncertainty. The proposed system is fabricated using commercially available discrete parts to power an MSP430F5594 microcontroller and a CC1352R wireless transceiver. The maximum variation in the measured charging time of the proposed system is only 1.5 seconds as the RF input power is swept from −4 dBm to +9 dBm. The maximum variation in the measured charging time for a traditional energy harvester under the same conditions is 17.3 seconds.