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Q: strong electromagnet required ( Answered,   0 Comments )
Subject: strong electromagnet required
Category: Science > Physics
Asked by: blochee-ga
List Price: $15.00
Posted: 04 Jul 2005 14:25 PDT
Expires: 03 Aug 2005 14:25 PDT
Question ID: 539901
I need to build an electromagnet which at the ends will have a field strength 
of 1.5 Tesla  (1 Tesla would be suffiecient at minimum).  The
electromagnet will be used for repulsion.

I have used an iron core and I am able to construct an electromagnet
of 0.15 Tesla but that is not strong enough.

Refer to the following page:

I also have a electromagnet with a air-core which reads about 35
Gauss.  If I were to put supermalloy in the air-core then will the
electromagnet be

35 Gauss * 100 000 = 3 500 000 Gauss  ?

I know something above is wrong.  Can you please tell me what is wrong
with the mathematics above?

So, what metal on the list is best to replace the air-core?  Also,
where can I get that metal?

Thanks in advance.
Subject: Re: strong electromagnet required
Answered By: hedgie-ga on 04 Jul 2005 21:06 PDT
It is not very complex: 

... the permeability is actually the slope of the BH curve. The
steeper the curve, the higher the permeability as shown below...

But a bit more complex then just multiplying H by permeability to get B:
 That BH curve is not a straight line,
 it reaches saturation, which depends on the material:

..The typical saturation flux density of Power Ferrite material is
under 4000 gauss (400mT). Whereas the saturation flux density of MPP
material is 7000 gauss. High Flux is 15,000 gauss and Iron Powder is
10,000 gauss...

   Cobalt based alloys have been developed which have high saturation :

The important series of alloys from cobalt?s point of view are the
Co/Fe series typified by Permendur ? this alloy being modified by
vanadium additions to improve ductility. The reason for the use of
cobalt is that this alloy benefits from the maximum saturation known,
23,500 gauss (2.35 Tesla) with a square shaped hysteresis loop, and
also from the high Curie Point.

 It all depends on Temperature too, of course - 
and required frequency response - and
 size and uniformity of field in a cavity...
do a search on
SEARCH TERM: curie point, saturation, hysteresis, slew rate

 You may want to learn from the people who build
 MRI machines and particle accelerators.

MRI equipment ranges from 0.2 to 9.0 Tesla,
accelerators use superconducting coils ..

Here is an example of 'state of the art' MRI:

"..High Power MRI Machine Coming to the Center for Biomedical Imaging
at NYU ... a team of scientists who designed and installed the world's
first 3-Tesla MRI ..."

 You did not describe the scope of the effort and resources.
 It gets expensive as you reach for higher flux density and size of the cavity.

 Here is a technical paper on design of MRI coils which reach  3T

Here is an example of 'your tax money at work' in  a national lab: 
They call 2.3 T a low field magnet
 (built with and limited by saturation of the iron core)
and mention  
rare earth materials and 'commercially available HTS' for 
design of High Density magnets.

It is a actually a field of study to which whole monographs and
courses are dedicated:

good luck


Clarification of Answer by hedgie-ga on 13 Jul 2005 08:24 PDT
If there are questions remaining, please, post a RFC
(Request for Clarification).
If all is clear, rating is appreciated.

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