A Broadband High-Efficiency Charge Pump for Ambient RF Energy Harvesting - Powering Underground RFID Based Sensors

This paper presents an investigation of the feasibility of harvesting ambient RF energy underground for the purpose of powering RFID-based sensors. A multi-band harvester composed of three individual Dickson charge pumps fed by a single bow-tie wideband antenna was produced then evaluated in performance both aboveground and underground. The device yielded a highest RF-to-DC conversion aboveground of 3.77 V featuring a 320 MHz bandwidth under a 10 kΩ load resistance and with a 475 MHz RF source of 20 dBm approximately 350 mm away, while with 200 mm of sand added between to simulate underground conditions, this shifted to 3.33 V with unchanged bandwidth. However, when the gap was increased to 600 mm, the above-ground performance was mostly unchanged while underground rectification performance declined, with rectified voltage reducing by 60% from 3.33 V to 1.31 V and the bandwidth shrinking by 47% from 320 MHz to 170 MHz. The RF-to-DC efficiency gap between aboveground and underground was found to shrink with the reduction of harvested RF power, a promising sign for the inherently low-energy ambient RF.