Tiny discs can levitate in the upper atmosphere using sunlight alone
An illustration of solar energy levitation discs
Schafer et al. Nature
Nail size discs that levial sunlight could one day carry sensors through some of the thinnest and coldest scope of the atmosphere. By stealing higher than commercial aircraft or weather balloons, such swarms could reveal new ideas on the evolution of the weather and the climatic models of the earth.
Levitation devices exploit a phenomenon called photophoresis. It was discovered for the first time more than 150 years ago when the chemist William Crookes invented the radiometer, a device with black and white blades that turn when exposed to the sun. This happens because the dawns absorb the light and give off heat, and this heat increases the momentum of the gas molecules around them. Because the black sides of the blades are warmer than the whites, they transfer more momentum to the gas, pouring the air in a direction with enough strength to turn the blades.
“We have taken this obscure physics and applied it to something that could really have an impact on many people – and help us better understand how things like the weather and the climate evolve over time,” said Ben Schafer at Harvard University.
To develop levitation discs, Schafer and his colleagues have created a device of 1 centimeter composed of two aluminum oxide sheets full of micro-scaling holes. When exposed to light, the lower leaf – which included alternating layers of chrome with aluminum oxide – heated more than the upper leaf, such as the black sides of the blades of a radiometer. This also created a directional air flow, but moving upward instead of laterally.
Under white LEDs and laser light – set to intensities equivalent to around 50% of the natural sunlight – this lifting force has levated the device. This is an improvement compared to other solar energy leaflets, which require light intensities several times brighter than sunlight. But the demonstration also took place under laboratory conditions with air pressure several thousand times lower than that on the surface of the earth.
Fortunately, these low air pressure conditions are common elsewhere – like the mesosphere, an upper layer of the atmosphere which extends from 50 to 85 kilometers above the planet. The researchers say that the reuse of their discs at 3 centimeters would allow them to transport 10 milligrams of payload at an altitude of 75 kilometers, bringing sensors to a region so difficult to study, it was nicknamed “the ignorosphere”. SCHAFER co -founded the rarefied startup of technologies to market swarms of such high flight devices for atmospheric surveillance and telecommunications.
After sunset, computer modeling suggests that the discs could stay in the air by exploiting the radiant heat of the surface of the earth. “If you can stay in the air at night, it is a big change in the simple installation or the fall,” explains Igor Bargatin at the University of Pennsylvania, whose laboratory does similar research.
Subjects:
