In a first, researchers at the University of Washington in Seattle have developed a completely tree-powered electrical circuit.
The nano-scale device—approximately 130 nanometers [a nanometer is one billionth of a meter] in size—consumes just 10 billionths of a watt (10 nanowatts).
Unlike the legendary science fair experiment in which a potato-based electric circuit is created using two electrodes (each electrode being a different metal, which react with the starch, causing a potential difference and thus a current), the UW device utilizes electrodes comprised of the same metal, and is able to generate (output) 1.1 volts. “As far as we know, this is the first peer-reviewed paper of someone powering something entirely by sticking electrodes into a tree,” according to paper co-author Babak Parviz, associate professor of electrical engineering at the UW.
Last year, researchers at MIT discovered that a constant current of about 200 millivolts (a millivolt is one thousandth of a volt) is generated between plant and soil. But that work did not involve attempting to power any device or circuit, which would require making a device capable of running (performing some function) on exceedingly low voltages.
The UW researchers sought to apply this knowledge to power an actual device. In seeking an ideal candidate power source under-graduate student Carlton Himes discovered that the broad-leaf Maple tree (common in the area) supplied a steady voltage of a few hundred millivolts. Despite this, the researchers realized that they would need a bit more juice to power a such circuit.
To solve this challenge, co-author and UW assistant professor of electrical engineering Brian Otis led a team that developed a “boost converter” which takes the low incoming voltage and stores it to produce a stronger output. The device is able to work with voltages as low as 20 millivolts and can output 1.1 volts–enough to power a small sensor that can be used to take the “pulse” of the tree (its periodic pulsing of electrical energy) which may indicate its overall health.
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