Who doesn’t love magnets? They’re functional, mysterious, and at the heart of nearly every electric motor. They can make objects appear to defy gravity or move on their own. If you’re like us, when you first started grappling with the refrigerator magnets, you tried to make one hover motionlessly over another. We tried to position one magnet over another by pitting their repellent forces against each other but [K&J Magnetics] explains why this will never work and how levitation can be done with electromagnets. (YouTube, embedded below.)
In the video, there is a quick demonstration of their levitation rig and a brief explanation with some handy oscilloscope readings to show what’s happening on the control side. The most valuable part, is the explanation in the article where it walks us through the process, starting with the reason permanent magnets can’t be used which leads into why electromagnets can be successful.
[K&J Magnetics]’s posts about magnets are informative and well-written. They have a rich mix of high-level subjects without diluting them by glossing over the important parts. Of course, as a retailer, they want to sell their magnets but the knowledge they share can be used anywhere, possibly even the magnets you have in your home.
Simpler levitators can be built with a single electromagnet to get you on the fast-track to building your own levitation rig. Remember in the first paragraph when we said ‘nearly’ every electric motor used magnets, piezoelectric motors spin without magnets.
29 thoughts on “Hovering Questions About Magnetic Levitation”
With a title like that one might think it had Benchoffian origins.
I’ve got plans to levitate my sofa with Neodiddlium magnets (AvE lingo). That’s because I’ve mounted a big bass speaker to the sofa to enjoy the vibrations of explosions, something which my neighbours don’t really enjoy. Hopefully by having it hovering above the floor the vibrations will at least not travel through the house structure directly.
I also thought about using magnets to mechanically decouple a test setup from the ground. What I am curious about is, since the repelling force of two magnets is non-linear, does that mean a single frequency will be converted to other frequencies? And is this energy leak towards other frequencies beneficial or bad concerning the attenuation of vibration like maybe hitting resonant frequencies of the hovering object? Has anyone experience with that?
If you are doing your levitating sofa, I would like to see the results.
hmm good point. Since the sofa will be vibrating and it is levitating on magnets, the force in the gravitational direction (Z) will be transmitted to the ground, the same situation as just putting the sofa on the floor. So perhaps that wouldn’t help as much as I hope :S
I don’t think any nonlinear frequencies will be generated, as the only variable thing here is the distance between the magnets, which depends on the gravitational pull. And that is dependent on the mass only.
Another option would be an air vibration isolation system like they use to isolate optical tables. It’s basically a set of four air bladders (one on each table leg) with some constrained degrees of freedom so the table top doesn’t slide around. Newport and TMC make these vibration isolation tables. The key is to have a large air capacitance and a large mass. Your couch provides the mass, so all you need are the bladders (and regulators, compressor, guides to prevent sliding around, valves…).
I think we are having a miscommunication.
Hovering your sofa on magnets will definitly change what and how frequencies from your bass speaker are transmitted into the floor. My points is I’m not sure how it will affect this.
Regarding my statement about non-linear repelling force:
I think the things that could happen in such a system are similar to what happens in a KTP crystal in optics (https://en.wikipedia.org/wiki/Potassium_titanyl_phosphate). The interaction between the electrical field in a electromagnetic wave (light) and the KTP crystal is non-linear. Meaning: IR light at 1064nm goes in and green light at 532nm comes out (in addition to the IR light; frequency doubles -> wavelength halves). In contrast a linear system can’t generate a different frequency.
So frequencies from your hovering sofa to the floor WILL BE transmitted, but I don’t know HOW.
Therefore my question is if anyone has experience with such constructions for attenuation of vibrations.
What exactly do you mean with “nonlinear frequencies”?
I think we’re talking roughly about the same thing.
I’ve seen non-linear distortion in other examples. For instance, I’ve done some research on measuring the compression of polyethylene blocks with an embedded parallel plate capacitor. By applying force to the block with the parallel plate capacitor inside, the capacitance increases with increasing force.
When you then apply a sinusoidally changing load, the capacitance also changes with a sinusoidal pattern, however, nonlinear distortion occurs; generation of predominantly 2nd order harmonics in my case. That’s what I meant with nonlinear frequencies.
This situation may be similar enough. Basically, this is a mass-spring system, with the sofa being the mass and the magnet being the spring.
It will have one or more resonance frequencies, but whether they’ll shift from the original location and whether you’ll notice it will be a different story. Perhaps the resonant frequency will be above 500 Hz or so, and the bass speaker doesn’t transmit frequencies that high.
Perhaps by levitating the sofa, it is no longer dampened by the floor, and will resonate at higher frequencies?
Wouldn’t some damped springs be 1000x easier? Presumably you’re talking about mounting them so they are constrained to move in 1 axis (since you can’t do free levitation with permanent magnets exactly as the article says), in which case they are acting like a damped spring anyway.
of course, but less cool!
Stick an iron plate in each back pocket and drive them with coils embedded in couch.
Just eat the magnets. Then you can feel the vibrations directly.
Heh, skin implants… probably easier to load a shotgun with magnetic sand and have someone shoot you in the butt.
That would be great for subwoofers too. The ultimate would be if you were the CEO of a mining colony on an asteroid with really low gravity. You would be able to have a “mattress” of computer fans and photocells and IR LEDs to levitate in the middle of your stateroom! To levitate your couch would use quite a bit of power because it’s fighting our gravity. Gravity sucks.
Nd magnets and pyrolytic graphite… Levitation without electromagnets or need for very exotic materials (i.e., superconductors and liquid N2).
So without following links to links to links, why is it that permanent magnets can’t be used for levitation? Are we talking totally “free” magnets – now that I can understand. But if both magnets are constrained, and can only move in, say, one axis (eg: up/down) – why not permanent?
Pretty sure it would work, constrained. There was some guy on HAD years ago who rigged his bed up with a ludicrous amount of magnets, to float. It was strapped to the floor at the corners with thick straps, which prevented the whole thing sliding off to a point where it either collapsed or was attracted to the magnets.
Sad thing was it wouldn’t work once anyone actually got into the bed. Only strong enough for an empty one. Which reduced the pointfulness of it by quite a lot, I thought.
Here y’are, kids! https://hackaday.com/2012/05/23/build-a-levitating-bed-for-under-1000/
The thing with magnets are that you can technically levitate them with just magnetic force, and no active control.
Simplest is to as you say, constrain both magnets, this can be easiest done with a tube that one magnet freely slides in, while the other magnet is firmly attached to the other side, then our free magnet that can slide in the tube is going to be floating on the magnetic field.
The problem gets harder if we don’t want to have anything mechanically locking our magnet in place, but do it just with magnets.
This can on paper be done, as we can in reality balance one magnet on top of another, but if it is slightly off, then the repelling forces will amplify the error until the system eventually fails.
Here we can actually do something different, as we can for an example have a box, that in each corner we have a magnet on it’s bottom, these line up with a larger diameter magnet on the floor. This system will at the moment amplify its misalignment until it fails.
This we can counteract by having a magnet on each vertical face of each corner, these magnets repel against an outer set of vertical magnets on some support attaching them to the floor.
If our box starts to wander, then the vertical magnets in the corner of the direction it is moving in will start to repel more against their corresponding outer pair. Therefor pushing the system back. And through this keeping everything in place. One can also do other implementations of these types of system to for an example also support rotation.
But at the same time, magnetism will make sure to screw with our practical setup to make sure this all gets fiddly to implement. On paper it can work, but there are many other things that work on paper by not so easily in reality.
I have actually built one of these floating boxes, but it is a bit unstable and fiddly to set up.
” Are we talking totally “free” magnets – now that I can understand.”
It’s Earnshaw’s theorem. It’s only for totally free magnets, and it only says there’s no stable *static* configuration of multiple magnets not at the same point (or charges, or masses). You need to have some other force providing constraints in order to be stable.
Add a constraint – any constraint – and it works fine. Put the system in motion and it’s fine, too, which is why a spin-stabilized magnetic levitation exists. Macroscopically, that requires constant power (since the magnetic forces are now trying to slow down the spin), although the same principle applies at a microscopic level for diamagnetism, which doesn’t require a constant power output because there simply isn’t a lower energy state to go to.
I have a passive electromagnetic system that is strong enough to suspend my 200lb+ mass 18 inches off the floor with great stability, reliability, and affordability. The electrons in each atom of its construction repel against each other while the chemical bonds between the atoms hold them together. The result is a crystal structure of great strength and durability that when organized appropriately, can be used for support. What is this great piece of technology? A common HON office chair.
Even hamsters like fridge magnets (sorry, I had to laugh): http://metro.co.uk/2017/07/06/pet-hamster-stuck-to-cage-for-three-days-after-eating-fridge-magnet-6759705/
Would you mind helping me with a magnetism question:
If I were to take a Ping Pong Ball and glue small circle flat magnets to it, completely covering the ball, lets say with ALL the North Poles facing out from the center.
And then take a non magnetic bowl and cover the inside surface of it with similar permanent magnets with all the North Poles facing upward (and inward at the edges as the bowl rounded up).
What would happen when I placed the magnet covered ball inside the bowl? For this experiment, all the magnets are superglued to their respective surfaces. the ball would have all north poles facing outward, and bowl would have all north poles facing up/in. The ball cannot leave the bowl due to gravity, but the ball cannot present any south poles because they are all facing inward toward the center of the ball and are glued in place.
Gravity should keep the ball inside the bowl. but the repulsive forces of the magnets should keep the ball levitated just above the magnets in the bowl. If this happens we would have permanent levitation using only fixed magnets. Would this be a violation of Earnshaw’s theorem, or am I missing something?
Please respond to CraigFlorer@gmail.com
Yorba Linda CA
Yes, Earnshaw’s theorem when applied here does not allow passive strictly magnetic levitation. I’ve spent more time playing with magnets than I probably should have and it has thoroughly taught me the relevance of Earnshaw’s theorem in pure permanent magnet situations. The ball in the bowl as you describe it will likely pop out of the bowl and veer off to the side to “escape”. Otherwise it will drop to the bottom of the bowl with gravity winning out over the magnetic lift. No floating can happen because there are no locations where the ball’s position is stable in both horizontal and vertical motion. All that said, the idea of the magnet covered ball and bowl are an elegant way to eliminate being concerned with magnets spinning around and reversing themselves. :-)
You KNOW you are going to make me end up having to DO this silly experiment damn you!
That wasn’t the goal. I was trying to discourage you, for your own sake. But if you must do it, you must. When magnets interact they never add to total system stability and things start out unstable before any forces are applied. They only trade one kind of stability for another with never a net gain. Because of that, Earnshaw’s law works with magnets in every arrangement of magnets I’ve ever heard of or tried myself. It takes a stabilizing effect from things like diamagnetic materials or something active, or temporarily with spinning tops and stuff like with the Levitron. (I’ve got one of those and have made it work, but it tests your patience. :-) )
If I violate any theorems or physical laws, I will post videos, (unless of course I cause the universe to implode by dividing by zero, or breaking universal laws)
if you had a ring of magnets not attracted to another group of magnets on a disc could you create enough lift to hover if you but a fan or or and rc helicopter blade on it
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