Materials

Graphite platform levitates without power

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The silica-coated graphite plate levitates above a magnetic surface, with no need for external power
OIST
The silica-coated graphite plate levitates above a magnetic surface, with no need for external power
OIST
A scanning electron microscope image of the graphite microbeads – green indicates the silica coating
OIST

Magnetic levitation is used to float everything from lightbulbs to trains, with varying levels of success, but usually it requires a power source. Now, scientists in Japan have developed a way to make a floating platform that requires no external power, out of regular old graphite.

If you’ve ever tried to push two magnets of the same charge together, you’ll understand the repulsive force at work. If the magnetic field is strong enough, objects made of certain materials (known as diamagnetic materials) can be made to effectively levitate above surfaces – which can be seen in plenty of showy levitating commercial products, from clocks to lamps to speakers. Higher-end tech uses superconductors to levitate heavier objects, enabling maglev vehicles that travel at high speeds with little friction.

The problem with all of these is that they require external power sources, and in the case of superconductors, close to cryogenic temperatures. So for the new study, scientists at the Okinawa Institute of Science and Technology (OIST) developed a low-cost material that can levitate above magnetic surfaces with no need for power.

It starts with regular old graphite, which is highly diamagnetic. That of course means it can levitate above magnets, but only for a short time – the flow of electrical currents through the graphite causes energy loss that quickly makes the levitating object fall. This phenomenon is known as eddy damping.

A scanning electron microscope image of the graphite microbeads – green indicates the silica coating
OIST

To prevent that, the team chemically coated the graphite particles with silica, which is electrically insulating. Finally, the coated graphite particles are mixed with wax and flattened into slabs measuring about 1 cm2 (0.2 sq in). In doing so, the graphite remains diamagnetic, but the insulation prevents the energy loss that would tank the levitation. And sure enough, in tests the silica-coated graphite platforms could levitate for long periods above a surface made up of magnets with alternating north- and south-poles.

The team says that this levitating platform system could lead to new types of sensors that measure force, acceleration and gravity. For even more precise quantum sensors, another version uses a feedback magnetic force to continuously correct the platform’s vertical movements, cooling it down to reduce its kinetic energy. The trade-off there, however, is that this does introduce the need for external power.

The research was published in the journal Applied Physics Letters. The levitating platform can be seen in action in the video below.

Source: OIST

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4 comments
rgbatduke
Bizarre. Breaking up eddy currents is old news, of course -- routinely done in electromagnet cores -- but even for "nanoparticles" of graphite if the diamagnetic repulsion is due to actual surface currents on the macroscopic particles (containing many, e.g. millions to billions, of carbon atoms) there should still be resistance heating and eddy damping of the induced magnetic fields. It's almost like the nanoscale particles are behaving like a superconductor, but not quite.

It'll be interesting to track this. I'm still having a hard time convincing myself that this will work at levels that revolutionize society as opposed to make a few toys and tools possible (cool physics demos, if nothing else:-) -- would this really support a maglev train on top of permanent magnets? Could one make the graphite composite in a strong field and "freeze in" a "permanent" magnetic field? Exactly how long are the "long periods" before eddy damping wins, and how does that scale with nanoparticle size?
Calcfan
The video is misleading. The point of the "news" was that pyrolytic carbon would be more efficient in a levitation demonstration. The video shows a steady field not a changing one - unless it is "constant" reaction to falling is what was meant.
Treon Verdery
I am wondering if keeping the electrical charge from conducting away with an insulator lay would function of piezoelectric crystals to make them stay flexed at a particular position longer, or deliver pressure longer, like at a robot finger, or piezoactuator at an afm microscope stage, the alternative, which is plating the piezoelectric crystal with a conductor could carry away electrons faster making earlier return to ordinary shape, that means you could drive the piezoelectric crystal at higher sonic frequencies and pulses per second, which would be great for earbuds.
Laszlo
At least a skechy scheme of the magnetic field konfiguration sustaining the levitation is needed. Very badly. Is it a trade secret they can't disclose it?