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Strong electromagnet to mr-fluid!

Strong electromagnet to mr-fluid!

Strong electromagnet to mr-fluid!


I really would appriciate some help on a project i am workng with!
I need a magnetic field as strong as possible in a limited space/weight. From a e.g. circular surface (approx 25-30mm in diameter) i need a protruding magnetic field. On this surface i will placce a "pillow" with magnetically changeable fluid, to be able to influence a pillow as thicck as possible i need the magnetic field to "reach out". The weight must be kept under approx 200g and the dimensions would preferrably be cylindrical with the surface as above and a length of approx 20-50mm (of cource i want it as small as possible, but i think it is easiest to maximize magnetic force according to weight).
I think i need a quite stong field up to at least 5-15mm out from the surface.

thanks in advance!

RE: Strong electromagnet to mr-fluid!

Have you tried any magnets so far?  It would help to narrow down the requirement "magnetic field as strong as possible".

I'd suggest starting out by ordering a cylindrical magnet from a catalog house (such as McMaster Carr or MSC).


RE: Strong electromagnet to mr-fluid!

Quick answer MagMike ;)

Yes, i got myself a cylindrical holding magnet with diameter 25mm and heiht 20mm, 12V DC 4W (farnell inone catalogue), should hold 140N or similar.
It has not nearly the effect i wanted.(slightley better when using 30V, but then it gets hot quite quick....)
Since this magnet got a centrum core connected with the outer rim (cover), producing north and soth both on the front surface ? , the magnetic field is quite "close" to the surface?
hope this produces more answers or questions to narrow it down. (have started to look for suitable copper wire...)

hopefull for more suggestions

RE: Strong electromagnet to mr-fluid!

So you need an electromagnet, that wasn't clear from your original post.

If I understand the description of your holding magnet, yes, it is designed to produce magnetic fields that stay close to the surface.  They aren't designed to produce fields that "reach out".

If you need on/off capabilities and fields that'll reach 5 to 15mm from the surface, you'll want a single core electromagnet: Basically a steel (or equivalanet material) rod wrapped with copper wire.  I'm not aware of standard products like that, but it is a simple construction.

I also re-iterate my suggestion of using permanent magnets (particularly rare-earth types), just to get a better estimate of the magnetic field strength requirement.

RE: Strong electromagnet to mr-fluid!

Is this for a class?

You need to QUANTIFY your requirements.  

I think it highly unlikely that an EM will work as well as a permanent magnet, unless you're willing to pump kiloamps and water-cool the EM.


RE: Strong electromagnet to mr-fluid!


Thank you fror your answers, and of cource exuse me for beeing unspecific. The first question is seldom the most formulated one.....

Yes, electromagnet.
Needed fieldstrength, no idea so far (though a very small flat circular permanent magnet D 9mm* t 1mm, probably neodym, had quite good effect giving me some hope...).
Not for class, for Ph.D project.
Yes, need to switch it on and off.
No cooling, got to be small.
So far just testing the idea.

I will probably proceed with making my own single core electromagnet. Can you recommend a SI steel number if there is a suitable for making a strong magnet, soft iron i suppose.

thanks in advance!

RE: Strong electromagnet to mr-fluid!

to MagMike:
You ment to use permanent magnets just to see if it works (or to convert the strength of those to what i need in an electromagnet)? Are permanent magnets "stronger" (size to force) than electromagnets by the way?


RE: Strong electromagnet to mr-fluid!

Yes, the suggestion for a permanent magnet is to get an idea of how strong & what shape magnetic field will work.

One a size to force basis, one can't say if a permanent magnet is more powerful than electromagnets.  Too many non-size factors are involved to be able to state one is stronger than the other, as a general rule.

Regarding your suggestion for a SI steel number: Go with something with the lowest amount of carbon as you can get.  Annealing the steel will help boost performance as well.

However, I agree with IRstuff, you'll get more power out of a permanant magnet with that size constraint, especially if you can't allow for cooling.  Shutting the unit on/off will be a challenge, but not an impossible one.  The magnet can be positioned on a device to bring it close to the MR "pillow" and then pull away when not needed.

RE: Strong electromagnet to mr-fluid!

Most PMs are coerced with a stronger field, but that comes at the price of power and heat.

As for shutting the field off, while I would otherwise hesitate to mention Steorn, their patent on switching magnetic fields is otherwise sound.  Essentially, you can use a mumetal shield and move the magnet in and out of the shield to turn off or even reverse the effective field.


RE: Strong electromagnet to mr-fluid!

I will go for low carbon steel, thank for the info.
At the moment though i will try to modify my "flat surface holding magnet" into a single core with backplate electromagnet (removing the surrounding "cup"). This is just a test to see how much further the field will reach out.
the problem with "movable" permanent magnets is that the pillows will move towards the magnet as it is closing in. I want to lock the shape, not move it while locking it, if you see what i mean (excuse my limited capacity of formulating my sentences in english).

IRstuff: very interesting company Steorn ;) , actually never heard of it until now, fun reading even if the concept is a bit......
Mumetal....i will look into that, i had a quick look but coulden't quite grasp the way that it worked.

ill do some more tests with my modified electromagnet and the ill probably get back with more questions!

thanks so far!

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