It's a shame though they can't position magnets such that no tethers are required. But probably health and safety wouldnt allow that.... after all
what if too vigorous action on the bed would push it off its magnetic cradle?
[Edited on 8-8-2006 by chemoleo]
Magnetic Bed
MadHatter - 7-8-2006 at 22:50
For the person who has everything - a maglev bed ! Not recommended for the dude
sporting a Prince Albert. Can you imagine that 911 call ?
EMS operator: What is the nature of your emergency, sir ?
Mr. DumbShit: My dick is stuck to the bed and it won't let go !
"Too vigourous action" - I'd like to give it a "test drive" with a woman ! hinz - 8-8-2006 at 13:23
I wonder which magnets they use, as permanent magnets are to weak, I think. If they use normal electro magnets, then the electricity bill will be
quite high or they might use supra conducting electro magnets. I saw once a similar construction, somewhere in a museum. It was basically a half
round magnet where the poles where at each end of the half round magnet. A magnetic rod (poles at each end) was placed on this magnet, so that the
same poles meet each other. Now the rod was floating on the magnet as it couldn't turn round due the half roundness of the lower magnet. The magetic
rod was held in this place by two small magnets at each end, they pushed the magnet till the repel- forces were in the equilibrium. The rod was
floating without any contact to other things. But if you lifted the magnet and turned it 180°, the rod was attracted by all magnets and was pulled
down. Maybe it's possible to realise such a self stabilisating construction as a bed too, but this would look only half as designed and cool like
this.
On the other hand I ask myself what happens if a person with a heart pacemaker, heavy ear rings etc. comes too close to it, would look quite funny if
these persons would hang on they ears and don't come away from it. I saw once a demonstration at a 300MHz NMR-Magnet and a piece of iron bonded at a
string. The string was attached somewhere so that the piece of iron was close to it but couldn't touch it. The distance between the magnet and the
iron was around 20cm. I never knew before that these magnets are so powerful.12AX7 - 8-8-2006 at 13:54
Hmm, static, no cooling, sounds like magnets repelling to me. Probably most of the price goes to buying all that neodymium and boron, not to mention
magnetizing it.
Guy wires, how tacky! The panacea of maglev is supposed to be levitation without any outside forces (or even supporting external forces). This
clearly misses the mark!
Timchemoleo - 8-8-2006 at 14:01
I agree, I don't think it's a superconductor as that would require liquid N2 cooling at least, and massive maintenance. It has to be neodymium
magnets. I seem to remember that there are materials that don't transmit magnetic fields (like Al?), so this is probably how the upper side is
protected.
As I said it's a shame it is tethered. I am surprised they can't constrain it by repelling and attracting magnets so that no tethers are required.
But, as I (and madhatter a bit more openly) pointed out, there are probably health and safety aspects to this.. just imagine the magnet flipped, and
you are inbetween
Does anyone know the field strenght of these magnets? I am surprised at the large distance, that must be half a meter at least. is a neobdymium magnet
capable of lifting another for half a meter, when constrained, i.e. in a tube?
[Edited on 8-8-2006 by chemoleo]12AX7 - 8-8-2006 at 14:17
Gnaw, aluminum blocks electric but not magnetic fields. You would use a steel case to shield the person, and any attachments, from the field.
Unfortunately, since magnetic monopoles do not exist, this would direct the north and south ends downward, dramatically reducing the field strength at
even a short distance.
They probably photograph it at dramatic angles to emphasize the height, but I'd bet it's little more than an hovercraft -- maybe less than a foot
(~0.3 m). Something that size, packed with enough magnets, will certainly possess a field large enough to push itself off. Consider a smaller magnet
forced a proportional distance above another magnet -- it looks about right. The magnitude of the total field energy just boggles the mind, that's
all.
BTW, as I recall, it is IMPOSSIBLE to statically levitate magnets without any restraint or active control (which wouldn't be static..). Reason being,
a magnetic dipole in an applied field experiences a torque as well as various lateral forces. It seems to me you might be able to apply three
torque-correcting magnet triplets (NS, SN, NS, the center magnet being attached to the axis with, say, a piece of aluminum) on opposing sides for each
dimension of freedom, in addition to the three sets at the center needed for lateral stabilization. Wait, the torque correctors would also act to
center it..
Timhinz - 8-8-2006 at 14:39
It's not impossible to statically levitate magnets as I explained in my first post, but I think my description was a bit difficult to imagine, so I
made a drawing (attachment). Just imagine that the magnets in the end are fixed by some plastic. The magnet gets only stronger repelled if it tries to
turn it in the vertical axis and the gravity avid it to turn in the diagonal axis.
chemoleo - 8-8-2006 at 14:44
Good point, you could have invisible magnets above AND below... magnets below that repell, and magnets above, suspended in the ceiling, that attract
(it'd have to be quite strong because of the distance). I imagine this should keep it afloat stably, particularly if the bottom floor magnet is formed
like a cradle, from which the magnet can only slip out by excessive physical force...
Would certainly be an interesting project to do for yourself, a small stable levitation chamber!
PS one problem I see is the damn flipping issue: it can always flip around the axis, then it is attracted to the bottom floor magnets, AND repelled by
ceiling magnets. Hmm I can see that this represent the more stable equilibrium.... Maybe the sides of the bed should contain vertical magnets which
are attracted by some in the walls or something...preventing the flipping issue.
[Edited on 8-8-2006 by chemoleo]Twospoons - 8-8-2006 at 14:48
Seems to me the photo posted is a fake. Looks like the designer has only made a 100:1 scale model - if I read the site correctly. The model is only
floating ~6 inches off the desk, which seems perfectly reasonable given the size of the magnet. The neodymium magnets I've played with are only small
(10mm diameter) - but will float at 10-15mm. The $150k price tag is stupid though. A magnet that size wouldn't cost more than $400.
You can suspend a ball bearing with static fields - just barely. Whats needed is a piece of diamagnetic material somewhere in the system (like
bismuth or graphite or liquid oxygen). Not very useful though, I gather the balance point is rather critical.
There is a mathematical proof somewhere that stable suspension is impossible just with magnets - though the guy's name ecapes me at present.
[Edited on 8-8-2006 by Twospoons]12AX7 - 8-8-2006 at 15:29
Diamagnetics are of course stable, but very weak. Superconductors are wonderful diamagnetics, but poor at anywhere near room temperature.
LOX is paramagnetic, not dia-.
Yeah, can't remember the guy the stability theory is named after.
Hinz: the floating magnet will flip its axis.
TimEliteforum - 9-8-2006 at 04:23
Quote:
Originally posted by hinz
I wonder which magnets they use, as permanent magnets are to weak, I think. If they use normal electro magnets, then the electricity bill will be
quite high
If you have 1.5million to spend on a bed, I don't think the electricity bill would be a worry.unionised - 9-8-2006 at 10:22
IIRC it's Earnshaw's theorem that says you can't have a stable, static array of magnets held "floating" in equlibrium.
If you use diamagnetic materials then the problem is easy enough to solve; I have a small magnet floating in mid air in my living room just as a
conversation piece. (I keep thinking that an induction motor to spin the magnet would be cool.
The real problem would be the cost of the magnets.Twospoons - 9-8-2006 at 17:55
Just for a giggle (because I'm particularly bored today) I modelled the repulsion with a magnetics FEA program called FEMM4. I put two strong
neodymium magnets of 1"x1"x.25" dimension, 40 MGOe magnetization at a distance of 2" and got a calculated force of 3N or 300g (appologies for the
mixed units). I can't imagine a magnet that size would weigh 300g so the resulting system should be able to float (if tethered, as in the photo).
FEMM4.0 is freeware - you'll find it easily with google. It solves 2-D planar and axisymetric problems in magnetics and electrostatics, and
electromagnetics. Good fun to play with, though the input drawing system is a bit clunky (who cares - its free!)not_important - 9-8-2006 at 18:02
If the bed itself used Halbach arrays then only a fraction of the field would appear above the bed.
Might be able to use permanent magnets for most of the lift, AC electromagnets in the floor and passive coils in the bed for the last bit of lift and
to provide stability. The electromagnets and coils effectively form a diamagnetic system, for more stability active control of the electomagnets
could be done.Twospoons - 9-8-2006 at 18:33
Oooo! Halbach arrays are so cool. I'm going to have to model that too now, damn you!
Edit: See attached simulation of two 10cm diameter halbach arrays, 10cm apart. Force (by Maxwells stress tensor integral) comes out at 22N.
The arrays are very crude, but you can see the big drop in field above and below the array.
[Edited on 10-8-2006 by Twospoons]
not_important - 9-8-2006 at 23:53
Quote:
Oooo! Halbach arrays are so cool. I'm going to have to model that too now, damn you!
(should I issue forth
an evil laugh?)
The arrays are used in the Inductrack system, which looks like a rather interesting maglev transport method. There's an outfit that wants to build a
personal public transportation system, SkyTran, around Inductrack.
Nice quite turn-around on the model.fescho - 13-8-2006 at 07:19
strong magnets cause headaches...
[Edited on 13-8-2006 by fescho]franklyn - 13-8-2006 at 18:10
Quote:
Originally posted by hinz
I think my description was a bit difficult to imagine, so I made a drawing (attachment).
There are devices which use feedback to dynamically vary
the supporting field so that a ferrous object can be levitated
beneath an electromagnet. The use of tethers in this setup
suggests there is no feedback circuit, and the bed is repelled
from below. Permanent magnets are inadequate to this task
as the size of the field would act to demagnetize them.
Diamagnetic levitation is only just feasible with pyrolytic carbon
and rare earth magnets, on a very narrow range. http://www.ian.org/Magnetics/Diamagnetic.html
A simple coiled A.C. seloniod in the floor , though very large ,
is sufficient , and the corresponding shorted coil wrapping
around the periphery of the bed.
A sign as can be seen in any MRI radiology clinic warning
of the danger of approaching with ferrous objects would
have to be prominantly displayed.
[Edited on 14-8-2006 by franklyn]unionised - 14-8-2006 at 09:14
Sorry to spoil the idea, but that set of magnets is exactly the sort of thing that Earnshaw's theorem proves won't work.jpsmith123 - 17-8-2006 at 18:30
Twospoons have you done any experimenting with Ansoft "Maxwell", a 2d and 3d, static, low frequency, and as of recently, transient, EM simulator?
They apparently have a "student version" available for download (after you register and are approved) that has less features available than the full
version, but it might still be useful.
I've tried earlier versions of Ansoft software, but after being spoiled by the user friendliness of CST "Studio" products, I found Ansoft just too
cumbersome. Although after looking at the info on the Ansoft web site, it seems the latest version of Maxwell, v11, may be much better.Twospoons - 17-8-2006 at 22:19
I've used the Ansoft 3d FEA package in a previous job - we had the full version on "evaluation" for an awfully long time. Don't recall which version,
but it was fairly easy to use. It could do some fairly impressive things with 3d sims. Like take 7hrs to run, while comsuming every last scrap of
system resource! Still I managed some rather lovely sims of the Halbach array we were using in our highspeed 300kW brushless DC motor - I was working
out the eddy current loss in the motor housing due to the end field leakage of the magnet array, hence the need for a 3d sim. 3D FEA takes a colossal
amount of computation - so I tend to stick to 2D now.
We also tried an FEA plugin for MATLAB - but the math was too esoteric for me, so I gave up chemoleo - 20-10-2006 at 18:22
So what easy, cheap materials are available to block or neuter magnetic fields?12AX7 - 20-10-2006 at 18:56
Cast iron is pretty cheap in absurd quantity.
Timchemoleo - 20-10-2006 at 21:17
Thank you, this occurred to me but is pretty mcuh useless.
Is the magnetic field truly blocked? I know transformers have a lovely iron core, but from what I remember testing, it can still be measured some
distance away from the transformer.
Say, in the instance of the floating bed above, say, I laid an iron sheet across the magnets that are located in the bed. Would there be virtually no
magnetic field *above* the iron sheet? How thick would the iron sheet have to be to achieve i.e. a 95% blockage, which would be i.e. required for
health and safety regulations (the 95% value of course depending on the actual strength of the magnets)? Is a 0.5 mm sheet enough? Or do I require 5
cm?
Specifics, 12AX. General answers with zero specifics aren't exactly going to help right?12AX7 - 21-10-2006 at 03:11
Specifics, Chemo. General questions with zero specifics aren't exactly going to help, right?
You asked about materials.
If you want to get specific about this case, then sure.
The total magnetic charge is zero, so neutralizing one pole necessarily requires neutralizing the other. That means N to S, which is an attractive
force. Slapping an iron plate on top, besides adding weight, will spread out the top pole, putting the "magnetic lines of force" closer to the bottom
pole's, neutralizing some of the bed-magnet's strength (or alternately, you can imagine the extended reach grabbing some of the floor magnet's top
pole; either works since magnetic fields obey superposition). Any total shielding will necessarily contribute an attractive force equal to the
repelling force, if the shielding is total. Also, a total shield is (on this scale, horrendously) rigid anyway, kinda-sorta defeating the purpose of
a "floating" bed in the first place.
On the other hand, you might be able to build a mattress tall enough that a magnet can be placed somewhere in the ceiling (perhaps somewhere the floor
above, given standard floor spacing), causing a region of zero magnetic field inbetween without severely repelling the bed. Come to think of it,
inbetween the two magnets there should be a region of approximately zero field (although it changes quickly in either direction!), so you could have
extremely intense magnets (several Tesla probably; nothing possible with current technology as far as I know) and hang the bed from the "floating"
magnet. (Nevermind what would happen if God suddenly felt like stopping the flow of virtual photons.)
. I never knew before that these magnets are so powerful.
