Electromagnet core shape vs field strength/shape

[Esedess]

Assuming the copper winding and overall core dimensions are identical, how does the shape of a core at its ends affect magnetic field strength and shape?

Flat edge VS sharp tip
(see attached PDF)

http://files.engineering.com/getfil...b-4e19-a6e1-fd59443d3d5b&file=Core_Shapes.pdf

Thanks!

 

[electricpete]

What attributes of core shape are you interested in?
What is the purpose of this device (inductor or electromagnet?)

Flat edge VS sharp tip

Can you explain what you mean by that? Does it have any relation to attached figure?


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(2B)+(2B)' ?

 

[Esedess]

@Electricpete: Thanks for the response!

I'm under the understanding that magnetic fields concentrate around sharp edges. If that's the case, it makes me wonder if a core that came to a sharp point at both ends would be stronger than one that was flat on each side. If not, it must have some effect still (in which case, I'm still curious about).. But I don't know enough about electricity and magnetism to decipher the all the variables.

This is for an electromagnet.

The "flat edge VS sharp tip" thing is depicted in my attachment. I drew up 3 different models to clarify what I meant (the first is an example of the common "flat" core edge electromagnet, and the other two are variations of my concept regarding a "sharp tip" core)

 

[electricpete]

Thanks. I didn't scroll down on first look. Now I see there are a series of sketches.

A pointed tip might possible create higher local flux density at the tip, but who cares it doesnt' buy you any holding power.

If you are looking for holding power, a flat surface of your will core will hold on to an attached flat steel piece much better than an irregular/pointed surface.

Also something to consider, U-shaped core such that the thing you're picking up bridges accross the U will tend to create much higher flux density (up to the point of saturation) and holding power than a geometry which does not complete the flux path.





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(2B)+(2B)' ?

 

[Esedess]

Forsure, I understand what you're saying about holding power. In my head, when I 1st questioned this, I wasn't so much thinking in terms of picking up/holding anything with the electromagnet, but more so magnetizing other objects that would pick things up, and manipulating ferrofluid. I probably should have mentioned that. My bad... I'm brand new to this whole forum.

Ok... So (just to really drive this home for me) IF instead of an electromagnet I was going for an inductor, how do you think the higher local flux density created by at the pointed tip would be more effective than a flat edge core?

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[EdStainless]

You can tapper the pole pieces to get higher flux density (same total field squeezed into a smaller are) only to the saturation limit of the material.
So I was building an electromagnet to reach ~2T over a 2" diameter, so we start with iron core wound to reach 1T on 4" and taper it to reach near saturation, then add tapered Permandure pole pieces to reach 2" and higher field density. Local filed density is higher but NA is the same.

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Plymouth Tube

 

[dgallup]

For long travel solenoids, conical pole faces have some advantage. However, a bigger factor is moving the working gap inside the coil winding. Ideally, the gap should be in the center of the winding but anyplace inside is better than outside. If you really want to experiment with the effects of geometry, get a 2D magnetic FEA program. There are commercial packages but you can download FEMM for free.

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.