A special type of plastic can make folded solar panels unfold on their own when exposed to sunlight. This might be helpful for the solar panels that power some spacecraft, which have to be launched in a small container and unfurled once they get into orbit.
Those types of solar panels are generally unfolded by some sort of external controller, whether that鈥檚 a mechanical system, like a coiled spring that is released, or a small motor. Chiara Daraio at the California Institute of Technology and her colleagues built a solar cell that unfolds itself using shape-memory polymers.
They started with a plastic ring taken from an expanding toy called a Hoberman sphere. The ring is composed of a series of joints that fold together like so many sets of scissors which allow it to compress to a much smaller size. The researchers replaced the hinges on their ring with polymers which expand when exposed to temperatures above about 35掳 C.
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They stretched a thin sheet of the shape-memory polymer across the middle of the ring, and covered that sheet with shards of solar panel. They arranged the shards so that when the ring was collapsed, the sheet would twist and the shards fold together in what is called a flasher origami fold.
When the entire folded apparatus was exposed to heat, the expansion of both the hinges and the creases in the central sheet caused the solar panel to unfurl, its surface area going from 5 square centimetres to half a square metre in under 40 seconds.
This could be used as a simpler solar panel for spacecraft that unfolds in the sunshine after launch, Daraio says. 鈥淭his polymer changes shape automatically, so you eliminate the need for all these other components [like motors and actuators],鈥� she says. It could also be used for more complicated unfolding objects that don鈥檛 unfold exactly flat, like radio antennas or even tents, she says. 鈥淚 think eventually that鈥檚 possible, we just have to get the origami right.鈥�
Journal reference:听Physical Review Applied,听
