Powering smart jewelry using an RF energy harvesting necklace

This paper presents a wearable RF energy harvesting device in the form factor of a necklace, suitable for powering smart jewelry. The design includes a U-shaped dipole antenna, matching network, RF-DC converter, and DC-DC converter. The system converts a 915 MHz RF signal into a constant 3.1 V DC output with an output power up to 106.5 μW at -6 dBm input power, sufficient to power a fitness monitor pendant in stand-by mode. An experimental comparison between multistage Cockcroft-Walton and Dickson RF-DC converters shows that the Dickson topology offers higher efficiency at high input power, whereas the Cockcroft-Walton converter performs better for low input power. The necklace can produce up to 23.2 μW at 10.4 m from a commercial isotropic 3 W RF power transmitter.