A new solar-powered flapping wing mechanism could enable engineers to dispense with the use of light-driven actuators in small drone, robotics and other industrial applications. The flexible bio-butterfly-wing developed by researchers in China requires no such hardware to reportedly flap even faster than those of butterflies.

A nanocrystalline metallic film is applied to a thin polymer sheet, and the bilayer structure is affixed to a support at one end. Uneven thermal expansion of the different materials on exposure to simulated sunlight causes the free end of the wing to curl upward, which in turn shades the metallic layer, causing the temperature to drop and the strip to unfold. A rapid flapping motion, clocked in cycles at up to 4.5 times a second, is produced by the repetitive curling and flattening of the wing.

The research team from Jiangsu University and Changzhou University demonstrated the bio-butterfly-wing in a light-driven whirligig, a light-driven sailboat and a photoelectric energy harvesting device. The highest frequency of flapping-wing motion documented was 4.49 Hz, which exceeds the frequency of real butterfly wings,

The design could allow robots to fly without the need for batteries or other external energy supply.

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