Tiny centimeter-wide featherweight disks made from two thin perforated ceramic alumina membranes joined by vertical supports can be levitated by photophoresis in very low-pressure atmospheres. Coating the bottom with chromium causes the lower surface to heat more than the top, so gas molecules bouncing off the warmer bottom gain more momentum and generate upward force. Perforations enhance thrust through thermal transpiration by channeling gas from cooler to warmer regions. Lab experiments simulating mesospheric pressure and sunlight showed passive floatation without onboard power. The devices outperform previous photophoretic flyers that required illumination brighter than sunlight, and could operate in Earth's mesosphere or on Mars.
The new centimeter-wide disks are made from two thin perforated membranes of ceramic alumina connected by tiny vertical supports. They are kept aloft by a force called photophoresis: the light-induced movement of small particles at very low atmospheric pressures. In lab experiments simulating mesospheric air pressure and illumination, the researchers showed that their devices could float passively, without any power source. Their paper reporting the results was published in Nature on August 13.
Photophoresis causes gas molecules to bounce more forcefully off the warmer side of an object than the cooler one, creating airflow. In this case, the research team coated the bottom of the disks with chromium to absorb light and heat up more than the top. Thus, gas molecules bouncing off the lower part gained more momentum than those at the top, generating lift similar to how a rocket's jet produces upward thrust.
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