As you may know, we (as in I and my research group) recently became more active in social media, in order to improve our visibility and thus attract more students into our ranks. As a part of our image crusade, we shot and edited (read: my colleague did) a few promotional videos about our lab. You have already seen one, so now is the time for another!
Behold, the UFO!
Or rather, since it’s not unidentified, it should be the FO! No wait, that can easily be misheard as something really…impolite.
UFO it is.
Since our resident Fox Mulder retired recently, and we thus lost our access to the Roswell artifacts, there’s nothing as fancy as graviton accelerators inside the saucer. But, in my honest opinion, it’s still much cooler than the drones and quadcopters that everybody is losing their mind about nowadays. And why’s that?
How it works
Well, the saucer has exactly zero moving parts.
Instead, inside the saucer there is a copper coil, wound in a flat solenoidal configuration across the saucer perimeter. When this coil is supplied with an AC current, it of course creates a magnetic field, passing through the saucer in the axial direction and then looping back beyond the perimeter.
The figure below should clarify the phenomenon. The figure shows the cross-section of the saucer, cut in half across it’s diameter. In the figure, the saucer is alone in space, far from anything interesting (such as ferromagnetic or conductive materials). The two violet boxes are the two sides of the coil, with the current flowing into to screen-direction on the right-hand side, and vice versa on the left. The black lines are the magnetic field lines, looping through center of the coil in the axial direction (up in the figure).
(Against my habits, I used the free FEMM software for analysis, since it’s quite easy and fast to use, and more than sufficient for this purpose.)
Now, this saucer obviously wouldn’t yet levitate. Indeed, in the video you saw that it’s floating above a white plate. That plate is aluminium, but any other conductive material would also do.
Now, once the time-varying magnetic field you see above tries to penetrate into the aluminium, the magic happens. According to basic physics, the time-varying magnetic field induces eddy currents into the plate. These currents are such that they oppose the change in the field.
Due to this reaction, the field gets squeezed near the surface of the plate. This is again illustrated below. The area between the two long horizontal lines is the thin conductive plate. As can be seen, the field lines hardly penetrate at all into the plate. Instead, most of them choose to skip along the surface.
This interaction between the magnetic field, and the inducing and induced currents is what finally levitates the saucer. The situation is mathematically quite complex to model precisely. However, the levitating force can be explained to a sufficient degree with some basic physics.
As you can see, the magnetic field near the plate is pretty much aligned in the plane, away from the center of the saucer axis. In other words, it’s radial. The currents induced in the plate, however, travel into the and out from the screen-plane, around the sauces axis. Hence, they are circumferential. So, the resulting force will of course be axial – pointing up and levitating the saucer just as desired.
Another reason it’s cool
And that’s one of the beautiful things about electrical engineering. Complex things can often be explained in a very simple way, and correspondingly expressed with a few simple equations – occasionally with a surprisingly high accuracy. In this case, I’m fairly certain that this entire levitation phenomenon could be compressed into a single T-equivalent circuit, like the one I showed you here.
And with this kind of a compact presentation, a control algorithm could be developed, allowing the UFO to move around.
And with that technology, we could actually build a true hoverboard. I should apply for funding.
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