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Thread: Researchers Levitated a Small Tray Using Nothing but Light

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    Researchers Levitated a Small Tray Using Nothing but Light

    One day a “magic carpet” based on this light-induced flow technology could carry climate sensors high in the atmosphere—wind permitting.

    In the basement of a University of Pennsylvania engineering building, Mohsen Azadi and his labmates huddled around a set of blinding LEDs set beneath an acrylic vacuum chamber. They stared at the lights, their cameras, and what they hoped would soon be some action from the two tiny plastic plates sitting inside the enclosure. “We didn't know what we were expecting to see,” says Azadi, a mechanical engineering PhD candidate. “But we hoped to see something.”

    Let’s put it this way: They wanted to see if those plates would levitate, lofted solely by the power of light. Light-induced flow, or photophoresis, isn't a breakthrough on its own. Researchers have used this physical phenomenon to float invisible aerosols and sort particles in microfluidic devices. But they have never before moved an object big enough to grasp—much less lifted anything that can carry objects itself.

    And it worked. “When the two samples lifted,” Azadi says, “there was this gasp between all four of us.” The Mylar plates, each as wide as a pencil’s diameter, hovered thanks to nothing but the energy from the light below, according to a paper published today in Science Advances. Energy from the LEDs heats up the Mylar’s specially-coated underbelly, energizing air particles under the plastic and propelling the plates away with a tiny, but mighty, gust.

    (And there you have the movie name. A Mighty Gust)

    This engineered structure is the first instance of stable photophoretic flight, and Azadi’s accompanying theoretical model can simulate how different flying plates would behave in the atmosphere. In particular, the model indicates that a levitating plate could mosey 50 miles overhead while carrying sensor-sized cargo. It’s an idea the lab members have floated as a way to study weather and climate...

    There’s a reason why scientists would want to get a tiny sensor into the under-explored mesosphere, which lies between 31 and 53 miles above your head. “Sometimes it's called ignorosphere, in joke,” says Igor Bargatin, a mechanical engineering professor at Penn and Azadi’s adviser, who led the study. “We just don't have access to it. You can send a rocket for a few minutes at a time, but that's very different from doing measurements using airplanes or balloons.”

    We haven’t ignored the mesosphere because it’s uninteresting; we’ve ignored it because it’s out of reach. The denser air below it affords enough lift to planes and balloons. And the thermosphere above is thin enough that air drag doesn’t burn orbiting satellites. The mesosphere gets the worst of both worlds—it’s too thin for lift but thick enough to burn an orbiter.

    That’s a drag for scientists, because the mesosphere is loaded with interesting phenomena, like weird blue and red lightning and the microscopic shrapnel of millions of meteors—shooting stars—scorching through it every day. The chemistry in that layer is also valuable for scientists interested in tracking ozone damage, according to Daniel Marsh, an atmospheric scientist at the National Center for Atmospheric Research. “Solar storms cause energetic particles to enter the mesosphere, creating nitric oxide,” Marsh wrote in an email to WIRED. That nitric oxide seeps lower into the atmosphere and eats away at Earth’s protective stratospheric ozone.

    (There's a cool video in the article).

    More here.

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