A unique new concept inspired by Aspen trees could serve as an emergency power backup for future missions to Mars.

Engineers often take their inspiration from nature, as evolution usually has come up with a solution for new problems. As a case in point, University of Warwick researchers may have found a possible backup power source for future planetary missions from an unusual source: trembling aspen leaves.

In nature, leaves might quiver as a way of regulating heat — while sunlight is essential to photosynthesis, overheating due to sunlight can shut the whole process down. Aspen leaves in particular appear to quiver more than most under even the slightest breeze. And while the movement isn't designed to generate energy, engineers thought the process could be co-opted to do so.

Every year over the past few years, third-year undergraduates at the University of Warwick have examined the deceptively simple problem of what makes Aspen leaves shake. Researchers at the university then took the problem one step further, undertaking a study to see whether this mechanism could effectively generate power. The results are published in Applied Physics Letters.

Making a Mechanical Leaf

The researchers showed that the leaf-inspired mechanism would work to generate electricity even when it's not all that windy. That makes the mechanism useful for places like Mars, where there the atmosphere is thin and even speedy winds don't carry much power. “With a thin atmosphere, efficiency of an energy harvester becomes particularly important,” says Petr Denissenko (University of Warwick).

Aspen leaves quiver greatly in low wind due in large part to the flat shape of their stems. Researchers mimicked this design with a cantilever beam that acted like the flat leaf stem, while a curved blade acted like the leaf. The resulting structure took flight more easily than the blunter bodies traditionally used for harvesting wind energy. The team didn't even have to replicate the stem's complex twisting tendency to get better than usual results — simply replicating a curved leaf and its flat stem was enough.

The key advantage of the new system, explains lead author Sam Tucker Harvey, is that it's a way to generate power without the use of mechanical bearings, which can seize up in extreme cold or become clogged with dust or sand.

Although the amount of energy produced would be tiny, it could nevertheless power wireless sensors. The applications for wind-generated energy could include weather sensors in remote locations, such as the Arctic or Antarctic, or in places where solar power is impractical. Or the harvester could serve as a backup power source, providing just enough power to keep a rover on standby. Such a power source might even have saved the solar-powered Opportunity rover, which fell prey to a planet-wide dust storm in 2018.

The next step will be to scale up the entire process and design a system for power generation than can be deployed in larger arrays. “The amount of available energy is a subject of ongoing research, with a typical value for palm-sized devices at the level of less than a milliwatt,” Denissenko explains. “The next nuance is what part of the mechanical power can we convert to electricity.”

There's still a ways to go before this concept is applied to particular applications, Dennisenko adds. “Still, we reckon most of the actual wind energy harvesters will be blade-shaped like ours.”

It may be a while, but one day, planetary rovers may be equipped with "quivering-leaf" power sources as standard equipment.