Electric cars are one thing, but how about solar-powered flying vehicles? We aren’t quite there yet, but one of the bedrock technologies of such a concept may have finally arrived. Scientists have developed a set of continuously flapping wings that derive their energy from the sun. In a study published in the January issue of ACS Applied Materials & Interfaces, a team of researchers led by Ningyi Yuan and Jianning Ding detailed how they built a “flexible-bio-butterfly-wing” using a thin polymer sheet covered in a nanocrystalline metallic film to drive motion.
Their artificial wing device (admittedly tiny) riffs on the concept of light-driven actuators, or systems that can produce a mechanical response using light as an input. These devices, while totally remote and simple to use, have the disadvantage of typically requiring a very high-intensity light source that is brighter than normal sun exposure. The researchers wanted to leverage materials science to come up with a system that could take natural sunlight and produce mechanical work.
To get there, they fixed one end of the aforementioned sheets of coated polymer to a support and hit it with a beam of simulated sunlight. The resultant temperature increase caused a major disparity in the thermal expansion between the layer of metallic film and the polymer itself. This caused the end of the sheet that was not attached to the support to curl up, creating a natural shade for the anchored end. This then made the temperature decrease and reverse the thermal expansion that had just occurred, thus flattening the entire strip back out … whereupon it was exposed to the full beam of light, and the process began anew. The end-to-end process can be seen here.
This cycle of folding, unfolding, and folding again created an effect that closely mimics the flapping of butterfly wings—only much faster. It has translated into real motion in simple experiments, too. The team fashioned a light-driven whirligig and even powered a miniature sailboat with natural sunlight using multiple sets of their artificial wings. These small-scale successes have given Ningyi Yuan, Jianning Ding, and their team confidence that the basic concept might someday be used to power larger initiatives. Sun-powered flying vehicles, anyone?