Electromagnet Question 1

[Razillian]

At this point I have a cylindrical dipole electromagnet with a 1008 steel core and encasement (no exposed copper wire, just a steel cylinder). I imagine the magnetic field looks like what I have depicted in Figure A below. My question is this: Is there a way to reconfigure the magnet so that is remains a dipole but to produce a field similiar to Figure B (note the elongated N pole field)?

(if the image doesn't show go here: [URL unfurl="true"]http://www.proverbsllc.com/images/electromagnet.jpg[/url])

Would removing the steel plating from the North end accomplish this? Or perhaps cupping (parabolic) the ends: S ( ( N ?

Any help is greatly appreciated.

-Andrew

 

[IRstuff]

Neither image nor link works.

TTFN

FAQ731-376

 

[Razillian]

Sorry, should be fixed now

 

[IRstuff]

see discussion in thread340-194101 regarding hard drive head actuators

TTFN

FAQ731-376

 

[Razillian]

Thanks, but I read that thread first before posting. I'm not worried so much about the shielding properties, I just want to make the N pole as strong as possible at as great a distance as possible. It seems like having the high permeability shielding to provide the "path of least resistance" around the circumference and S pole, but leaving the N pole open would work for what I need, but I am looking for verification that it would not weaken the field.

I also remember a discussion about using parabolic shaped ends might produce an extended field. So those are my two ideas for this, but I am looking for either confirmation or alternates.

Thanks,

-Andrew

 

[israelkk]

The pictures are incorrect. The casing is all over the coil therefore almost all the magnetic flux will pass in the iron/steel casing. Only if the iron is saturated some flux will pass through the air.

 

[sreid]

Check out a two magnet Halbach array.

http://en.wikipedia.org/wiki/Halbach_array

This should work just as well for an electromagnet.

 

[IRstuff]

The Halbach array seems to be a more complicated version of the hard drive head actuator. The iron backing of the magnet mounting does the same thing as the lateral magnets in the Halbach array, by terminating the fields of the hidden poles, thereby shielding the backside.

see:

http://www.etel.ch/cms/default.asp?Id=372

versus:

http://en.wikipedia.org/wiki/Halbach_array

TTFN

FAQ731-376

 

[prex]

Razillian,
a magnetic dipole (remember that magnetic monopoles do not exist) is just like, in electrical terms, a battery: the load (e.g. a lamp in the electrical parallel) is represented by the air gap between the poles, whilst any ferromagnetic component added to the flux path is like a conductor wire.
By reasoning in this way you'll easily understand that there is no way for a simple dipole to increase the flux on one pole at the expense of the flux on the other one: just like the current in a circuit is the same near the positive lead and the negative one, the flux will be the same.
And as I told your colleague Greavis on another thread, if you don't explain the purpose of your magnet assembly, you'll not be able to receive more help on how to achieve your goal.

prex

http://www.xcalcs.com

: Online tools for structural design

http://www.megamag.it

: Magnetic brakes for fun rides

http://www.levitans.com

: Air bearing pads

 

[MJR2]

As has been said if this device is totally enclosed external magnetic field will be present only if the steel is saturated.

Having a core and then a backbar on one end will project the field in one direction. The bigger the diameter of the core and the bigger the backbar the further the field will be projected.

A starting thickness for the backbar is to provide the same cross section as the core at their intersection.

Some dimensions and detail would make this analysis much easier.

Mike

 

[Razillian]

Here is a basic image (hopefully working this time around) of what I am trying to accomplish. Two electromagnets, one fixed in position, the other below (and kept from dropping completely out) holding a weight (the 1lb is just to show it is a weight). The idea is for both electromagnets to be turned on thus lifting the weight a distance of approximately 1/4". This works with my current configuration, I just need to maximize the weight that can be lifted without going over the current/voltage available.

I refer to the magnets at dipole only in that I can't do a configuration to U shape the electromagnets. Space is limited, as is the voltage that can be supplied to the magnets (about a 6 volt source).

The electromagnets each have the following dimensions:
Core Diameter: 0.125"
Core/Coil Length: 0.25"
Coil Diameter: 0.375"
Currently using 30awg wire for the coil.

My understanding of magnetics stems from my electronics background, that is to say I know electronics just never specialized into magnetics. That said, I have always understood that any force (electrical, light, etc) can be focused to some degree. We use lenses and parabolic mirrors to focus light. We use magnets to focus lasers or partical accelerators. We use low resistance wiring to focus electricity (as opposed to a big hunk of metal that has eddies all throughout). Etc.

My thought with this is that by using a material with high permeability on the sides and one end of the electromagnet, the "juice" would flow more readily to the other end, providing more (or less reduced?) flux at the open end. Sort of like reducing the resistance before a light bulb so you get max energy at the bulb.

Mike, by "backbar" do you mean the end of the magnet facing away from the other (in my picture above) such as the S pole on the bottom electromagnet?

Hope this all explains some of what I am trying to do and can help everyone out there shed some ideas on ways to accomplish this.

Thanks,
-Andrew

 

[MJR2]

To focus a magnetic field one uses steel or other magnetic fields.

The backbar is what you describe on the S pole and extended to the sides.

The coil you describe given a perfect lay will be about 260 turns of wire. 20 watts of power is required at 6 VDC. This gives you about 880 ampturns. Not much to work with. A 0.125 dia core will have very little projection. Even conserving all the flux possible.



Mike

 

[MJR2]

Your circuit with 1/4 inch between the magnets will provide a force of about .25 lbs with and 0.2 lbs without a backbar and sides.

The core of 1010 steel is saturated thru about 3/4 of it's length.



Mike

 

[Razillian]

Thanks Mike. Another question, would a better core/backbar material such as MuMetal provide any noticeable improvement?

 

[MJR2]

I do not have a curve for MuMetal but I used vanadium permendur. It improved things a surprising amount. The solution suggests 0.48 lbs force. Core is still running at 2T just not saturated now.

You need bigger core and more ampturns for a pound force.

Mike