Instead of a sensor that flips on or off at a certain field strength, the tiny chips supply a voltage that varies with the strength of the magnetic field it sees. If the magnetic field gets stronger, the voltage goes up. They're great for sensing tiny changes in magnetic field strength. There are three of these sensors located at the center of the device.
They are oriented to sense the magnetic field in each direction: up and down, left and right, fore and aft. Armed with a bit of magnetic knowledge, the readings from these three sensors provide enough information about the height and position of the floating magnet. When the floating magnet tips off to the side, the system can sense it from these inputs and turn on the right electromagnet to give it an correcting push.
This device has three sensors and four separately controlled electromagnets. We hooked up an oscilloscope to two interesting points:. The sensor signal, shown in yellow, is very noisy.
Ignore the noise, though, and just look at the overall voltage level. We saw that it gets higher or lower depending on the position of the magnet. It sits around 1. The blue signal shows the voltage to one of the electromagnet coils.
It goes up to about 2. When we touch the floating magnet, it goes on longer. You can see this in the width of the up-time signal.
This control of the electromagnet flips on and off at kHz. We had hoped to hook this signal into a speaker to allow us to hear it as sound. It would be neat to hear that interactive audio feedback. Sadly, kHz is far above the highest frequency humans can hear. We would have to either downsample the signal, or ask some dolphins what they think about it.
The other three are working in similar ways to counteract tilts in the other directions. In addition to using the four electromagnets individually to prevent the floating magnet from tipping away in any direction, the whole system must also control the overall signal level to all four electromagnets. For example:. We have a levitation kit we acquired years ago that has a much simpler setup.
This setup flips the system upside down, making things a lot easier. It has a single electromagnet positioned above the floating magnet. The electromagnet flips on and off to control the vertical position of the magnet.
Like a long pole hanging down, you get natural stability in this configuration. We hooked this one up to the oscilloscope as well and found a different control scheme. When the magnet starts getting too low, it turns on to pull it up. When the magnet starts getting too high, it turns off. The frequency of this on and off switching varies depending on what the sensor says.
When you see electronic products that levitate something using one of these two basic setups, you can usually figure out which one it is. If there's something above the floating object, it's this second, simpler system. If there's nothing above the floater, it's the first. Once it is cold enough to exhibit superconductivity, however, those magnetic fields get expelled. Any magnetic fields that were passing through must instead move around it. Follow Jennifer Hackett on Twitter. Already a subscriber?
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