Ultra-low power 2.4GHz RF energy harvesting and storage system with −25dBm sensitivity

An RF energy harvesting and storage system is described that trickle charges a battery from incident power levels as low as −25 dBm referred to the feedpoint of an 8 dBi patch antenna. The circuit is optimized for the indoor ambient power range typically observed in the 2.4 GHz ISM band so that we can harvest the energy provided by nearby Wi-Fi, Bluetooth and other devices. In this incident power regime, rectified voltages are low, so power management circuit operation in the 100mV regime is critical. We present several improvements to our prior work that significantly improve its performance, including a novel wideband multi-element antenna array, an improved boost converter, and a redesigned battery charger. At −25dBm RF input power, the new harvesting system sources 150μJ into a rechargeable battery after 1 hour. We believe that this work represents the lowest reported startup power yet achieved in battery-storage RF energy harvesting systems.