Illustration of a solar-powered levitating disc
Schafer et al. Nature
A tiny disc, roughly the size of a nail, has the potential to ascend to high altitudes in sunlight while carrying sensors through some of the coldest and thinnest parts of the atmosphere. These swarms, flying higher than commercial aircraft and balloons, could reveal new insights regarding Earth’s evolving weather and climate.
These floating devices harness a phenomenon known as photophoresis. This was initially discovered over 150 years ago when chemist William Crookes invented a radiometer, a device with black and white feathers that spin when they are exposed to sunlight. The wings absorb light and release heat, increasing the momentum of nearby gas molecules. Due to the difference in temperature between the black and white sides of the wings, the black side emits more momentum, allowing the air to flow in one direction with sufficient force to turn the wings.
“We’ve embraced this lesser-known physics to develop applications that could benefit many people, enhancing our understanding of how weather and climate change unfolds over time.” Ben Schafer from Harvard University.
To create the levitating disc, Schafer and his team designed a device that spans 1 cm, composed of two sheets of aluminum oxide filled with microscale holes. When illuminated, the lower sheet, which contains alternating layers of chromium and aluminum oxide, heats up more than the top layer, similar to the black sides of the radiometer blades. This generates a directional airflow that moves upwards instead of sideways.
Under white LED and laser illumination — set to an intensity that mimics about 50% of natural sunlight — this upward force successfully lifted the device. This represents progress over previous solar-powered flyers, which required light intensity significantly brighter than sunlight. However, the tests were conducted under laboratory conditions with air pressure much lower than Earth’s surface pressure.
Fortunately, such low pressure conditions are common at higher altitudes, especially in the Mesosphere, which spans 50-85 km above the Earth. Researchers indicate that increasing the disc’s size to 3 centimeters could enable it to carry a 10-milligram payload to hard-to-reach research areas at altitudes of 75 km. Schafer has co-founded a startup, Rare Feed Technology, aiming to commercialize fleets of these high-flying devices for environmental monitoring and communications.
After sunset, computer modeling indicates that these discs could utilize the heat radiating from Earth’s surface to remain airborne. “If they can stay afloat during the night, that represents a significant advancement instead of simply descending and landing.” Igor Bargatin from the University of Pennsylvania, who is conducting similar research.
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Source: www.newscientist.com
