Ferns provide model for tiny motors powered by evaporation

Sep 14, 2006
A cluster of actual sporangium

Scientists looked to ferns to create a novel energy scavenging device that uses the power of evaporation to move itself -- materials that could provide a method for powering micro and nano devices with just water or heat.

"We've shown that this idea works," said Michel Maharbiz, assistant professor of electrical engineering and computer science and principal investigator in the group that built the device. "If you build these things they will move. The key is to show that you can generate electricity from this."

As often happens, the research started while doctoral student Ruba Borno was exploring another idea entirely. Borno was interested in mimicking biological devices, specifically microchannels that plants use to transport water, so Maharbiz gave her a book on plants.

But something else in the book caught her attention – the section on how ferns spread their spores.

"It's essentially a microactuator," said Maharbiz, meaning that the fern sporangium transforms one form of energy, in this case heat via the evaporation of water, into motion. When the cells in the outer wall of the sporangium were water logged, the sporangium remained closed like a fist, storing the spores safely inside. But when the water in the outer wall evaporated, it caused the sporangium to unfurl and eject the spores into the environment.

The researchers examined some fern leaves under a microscope. They found that when exposed to light or heat or any evaporation-inducing event, the sporangia opened and released the spores.

"Once we saw that, we thought, ‘Oh, we have to build that,'" Maharbiz said.

The method for making the material is simple enough. A wafer is coated with silicone and the hit with light, causing a pattern. The residual pattern is lifted off and that is used for the device. It resembles a curved spine with equally spaced ribs fanning outward from the spine.

To make the device move, Borno said, they load the space between the ribs with water, and when the water evaporates, the surface tension of the water pulls on the tips of the ribs so that the tips move toward each other, straightening out the spine of the device. In this way, the closed device opens wide—it moves.

They plan to add electrical components to the device in an attempt to generate electricity. They predict that the device will be able to generate the same amount of electricity as other scavenging devices, say, a solar cell in a calculator.

The ideal application, Borno said, would be to power a remote sensor where it's impossible to change the batteries regularly.

Click here to see video.

Source: University of Michigan

Explore further: 'Bulletproof' battery: Kevlar membrane for safer, thinner lithium rechargeables

add to favorites email to friend print save as pdf

Related Stories

Can technology stop scourge of bicycle thefts?

Jan 21, 2015

Urban cyclists have more in common than an aptitude for pedaling through city streets - they share the ever-present dread of one day discovering their bicycle missing from the bike rack, or finding only the skeletal remains ...

Robot looks like a fish to ride with marine life

Jan 02, 2015

(Phys.org)—Students at the Swiss Federal Institute of Technology (ETH) in Zürich are working on a project that could deliver an ideal device for marine life filming, minus the turbulence and appearance ...

Out with the keyboard as talk takes over typing

Jan 15, 2015

With the recent acquisition by Facebook of voice-recognition company Wit.ai, all four major players in the post-PC market (Apple, Google, Microsoft and Facebook) now have a significant infrastructure for ...

Reaching across the sea for the sake of water

Jan 09, 2015

The Arava desert, a salty wasteland dotted with tufts of scrub, gets only about an inch of rain each year. And yet cows lazily low at dairy farms that collectively produce nearly 8 million gallons of milk annually. Orange ...

From quirky to revolutionary, the CES show has them all

Jan 09, 2015

Sure, the International CES show was chock full of connected cars, smart home sensors, music gear and computer gadgets, as you'd expect. There were even drones buzzing the 160,000-plus people that tromped ...

Recommended for you

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.