Many MindedGraphene coil runs a thermometer on the hum of household wiring
Researchers at the University of Arkansas and the University of Michigan have built a graphene-based harvester that produces electricity from ambient radiation near electrical wiring. They demonstrated it in a battery-free temperature-sensing system: the harvester, power conversion circuitry, energy-storage capacitors and an ultra-low-power temperature sensor. The study was published in the Journal of Vacuum Science and Technology.
The mechanism is electromagnetic induction. The changing magnetic field around AC wiring, which in the US oscillates at 60 Hz, induces a small alternating voltage in an inductor the team made from graphene, with a steel core to improve capture of the field. A circuit based on a Cockcroft-Walton voltage multiplier converts the AC to DC and raises the voltage enough for the sensor. Energy goes into three capacitors rather than a rechargeable battery. The custom sensor runs at the nanowatt scale, which the article says is about 30 million times less power than a single AirPod uses, and the researchers say the inductor charges the capacitors faster than the sensor drains them.
This matters because sensors are cheap to build but costly to maintain. Replacing batteries across thousands of devices is labor and waste. Prof. Paul Thibado, the harvester's inventor, says stored charge can run the sensor for at least 24 hours during a power outage, and probably about a week. Suggested uses include large industrial facilities, product tracking, fleet logistics, soil and wearable monitoring, and medical tracking.
The caveats are real. The harvester needs sufficiently strong changing magnetic fields near wiring, so it cannot generate power anywhere. The team has not shown it can start from a fully discharged state; the capacitors were pre-charged and the processor programmed beforehand. Nanowatt output powers little beyond the dedicated sensor, so this does not point to self-charging phones. Uses beyond temperature sensing are envisioned, not demonstrated. The team is also studying acoustic, nonlinear, solar, thermal and kinetic sources, aiming for sensors powered from several sources.
Source: New Atlas