At University of Pennsylvania in the mechanical engineer Igor Bargatin’s lab, Mohsen Azadi and his team were able to successfully demonstrate levitation of an object using light. Team built a “nanocardboard,” a material that’s as thin as a few strands of DNA and weighs less than a thousandth of a gram, but stiff enough to resist flopping for levitation.
Crookes radiometer – also known as a light mill, the instrument is essentially a glass bulb under partial vacuum with paper vanes that are black on one side and white on the other.
When the radiometer is exposed to sunlight, the black sides of the vanes absorb some of the energy and heat up a little bit.
“What’s happening then is the air molecules hit the black side, absorb some of the heat, and then leave with a higher speed than it came in with. In physics, we know that whenever you have a change of momentum, or speed, there must be a recoil, there must be a reaction force. The recoil pushes harder on the hotter black sides than the cooler white sides of the vanes and can make the Crookes radiometer rotate pretty quickly if you put it out in direct sunlight.”
The force observed and use is a thermal effect, based on the interaction between the gas molecules and a heated solid.
No one up till now was able to use these forces to overcome gravity and make the vanes levitate until this project.
New nanocardboard plates, because they’re so light, thermal forces that are too small to lift paper can lift the nanocardboard pieces into the air.
Azadi, who is studying mechanical engineering, came to the project after an element of another project he was working on, involving blood filters, seemed applicable to the levitation project.
Igor Bargatin is the Class of 1965 Term Assistant Professor in the Department of Mechanical Engineering at the School of Engineering and Applied Science at the University of Pennsylvania.