September 8th, 2009
An electrical circuit that runs entirely off power in trees
You’ve probably already heard of the idea of harvesting electricity from body heat to power small devices, such as those in the far-flung idea of a body area network. Now, a similar idea has been applied to trees. There’s enough power in trees for University of Washington researchers to run an electronic circuit, according to results to be published in an upcoming issue of the Institute of Electrical and Electronics Engineers’ Transactions on Nanotechnology. They found that the power is minuscule, but measurable, and enough to power circuits.
This custom circuit can store up enough voltage from trees to run a low-power sensor. Credit: University of Washington
“As far as we know this is the first peer-reviewed paper of someone powering something entirely by sticking electrodes into a tree,” said co-author Babak Parviz, a UW associate professor of electrical engineering.
The UW team was not the first to discover tree power. A study from last year at the Massachusetts Institute of Technology found that plants generate a voltage of up to 200 millivolts (a millivolt is one-thousandth of a volt). The UW researchers, however, say they took it a step further and successfully built circuits to run off that energy for the first time.
Now, let’s discover how the team accomplished this. First, they hooked nails to trees around the UW campus and connected a voltmeter to them. They found that the bigleaf maples generated a steady voltage of up to a few hundred millivolts. Next, the UW team built a custom boost converter- a device that takes a low incoming voltage and stores it to produce a greater output- that was able to work with input voltages of as low as 20 millivolts, an input voltage lower than any existing such device. It produces an output voltage of 1.1 volts, enough to run low-power sensors.
The circuit they developed is built from parts measuring 130 nanometers and it consumes on average just 10 nanowatts of power during operation (a nanowatt is one billionth of a watt). Parviz explained what to expect at this scale:
Normal electronics are not going to run on the types of voltages and currents that we get out of a tree. But the nanoscale is not just in size, but also in the energy and power consumption. As new generations of technology come online, I think it’s warranted to look back at what’s doable or what’s not doable in terms of a power source.
As for applications for the tree powered circuit, Parviz said that it could provide a low-cost option for powering tree sensors that might be used to detect environmental conditions or forest fires, and the electronic output could also be used to gauge a tree’s health.
“It’s not exactly established where these voltages come from. But there seems to be some signaling in trees, similar to what happens in the human body but with slower speed,” Parviz said.
“I’m interested in applying our results as a way of investigating what the tree is doing. When you go to the doctor, the first thing that they measure is your pulse. We don’t really have something similar for trees,” he added.
Carlton Himes, Eric Carlson and Ryan Ricchiuti of the UW were also co-authors of the study. The research was funded in part by the National Science Foundation.
Source: University of Washington News
Christopher Jablonski is a freelance technology writer. Previously, he was the manager of marketing editorial at CBS Interactive, delivering client solutions on BNET, ZDNet, and TechRepublic. See his full profile and disclosure of his industry affiliations.
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