Last year, MIT researchers found that plants generate a voltage of up to 200 millivolts when one electrode is placed in a plant and the other in the surrounding soil. A University of Washington team followed up on this research, and has run a custom circuit entirely off tree power.
By hooking nails to trees and connecting a voltmeter, Carlton Himes, a UW undergraduate student, found that bigleaf maples generate a steady voltage of up to a few hundred millivolts.
The UW researchers next built a device that could run on this available power. Brian Otis, assistant professor of Electrical Engineering, led the development of a boost converter - a device that takes a low incoming voltage and stores it to produce a greater output.
The team's custom boost converter works for input voltages of as little as 20 millivolts, an input voltage lower than any existing such device. It produces an output voltage of 1.1 volts, which is enough to run low-power sensors.
The UW circuit is built from parts measuring 130 nanometers and it consumes on average just 10 nanowatts of power during operation.