First option is to wind a Helmholtz coil to get a fairly homogenous volume in space with good access. Lots of info online, my quick calculation says with a diameter of 20 cm, spaced 10 cm apart, you need 6600 ampere-turns to get 60 gauss. Wind 1000 turns on each coil and put 6.6 amps through them in series, and from memory the homogeneity will be in the percent or better range for a sphere about 1 cm dia. I think the book "Building Scientific Instruments" has a good discussion, too - every analytical chemist should have that book on the shelf and regularly reread it :-).
Second option, go to
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and put N42 material, 1" dia, 0.03125" thick, and 2" spacing into the gap calculation. I get 70 gauss across the midplane with good uniformity out to about 1" dia, by eye. Don't know about in the vertical direction, but it should be ok near the midplane. Their part DX001 is $1.44 each/1, $1.41 each/10, get 10 to play with along with some of their large size magnetic pushpins (great stocking stuffers, yes, I'm a satisfied customer). Use 3/4" PVC pipe, cut a piece 2" long and drill a 3/4" hole perpendicular to the long axis at the middle, stick a disc on each end, and put your solenoid in the cross hole. Play with KJ's calculator to try different diameters and spacing - the problem is you need an appreciable diameter to get the uniformity up, and then the field is already 10x too high until you run the spacing so far apart the uniformity is falling back down (best uniformity is at a spacing equal to the radius of the disc, measured from the center of each disc).
Get one of those 3-1/2 digit 3 tesla max meters off ebay to measure and map and you are in business. Adjust the tube length as needed to change the field. Go wild and thread two pieces together so you can just unscrew them a little to drop the field :-). If you really want a better estimate of the uniformity over some volume download the free program femm and model it, or send me an email and I'll run it for you.
We have a requirement to design a gadget that will work in a 0.06T static magnetic field, and we want to use some miniature telecom type relays. They are not specified for field tolerance. So we need to make such a field and test them.
A simple ring coil of 2 cm radius needs 2000 ampere-turns, kind of messy.
I guess we could buy a big lab-type electromagnet, but that's a hassle.
Maybe something could be done with a couple of these, back-to-back in a steel pipe.
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If course, we'd have to get some sort of field sensor to calibrate it. With a ring coil, or a solenoid, we could just do the math.
If we had a sensor, maybe we could hack up something with PMs and bits of iron or something. Maybe pave the faces of a machinists's vise with supermagnets?
Any ideas?
Anybody got a big lab magnet?