Graphene powerline energy harvester powers a batteryless sensor

Autonomous Internet of Things sensors require practical ways to obtain operating power from their surroundings. In this study, the authors crafted various two-dimensional spiral and three-dimensional helix graphene inductors. The inductance was characterized by measuring the current through the inductor as a function of both applied voltage and frequency. Next, the induced voltage and current produced inside the graphene inductor were measured as a function of the current flowing inside a nearby power cable. A single graphene inductor with an inner steel core can produce a voltage high enough to activate a Cockcroft–Walton (CW) circuit. The CW circuit passively rectifies the inductor signal and multiplies its amplitude. Different multiplier stages are used to charge three different storage capacitors up to the voltage levels required to operate a custom low-power-consuming temperature sensor system. The basic operation and performance of the sensor system are presented. Replacing the usual power-management chip and rechargeable battery with these storage capacitors lowered the sensor’s overall power consumption and extended its projected service life. The demonstrated sensor operates after a one-time stage in which the storage capacitors are initially charged and the CPU is programmed; autonomous cold-start operation was not evaluated.