maximum Axial Field

[bquinn]

For a round electromagnet, is there a general rule for the orientation that provides the maximum field along the axial centerline. Specifically, is there a ratio or relationship between the OD, ID and height of the coil that will maximize the field. Given a set # turns, the coil can be designed many ways (e.g. greater height with smaller OD, vice-versa, etc.). I have attempted to plot this theoretically but haven't been able to come up with a trend towards an optimal design.

Thanks in advance for your help.

 

[MJR2]

A few tips.

Shorter cores are better. Generally longer cores become saturated.

To project field requires a larger diameter core.

You need to at least partially saturate your core.

Your surface area must be able to disapate the heat from your coil.

Bigger OD coils will project more field. But not much as compared to smaller.

Build one and it can be scaled. The field projected will scale but not the force.

Mike

 

[bquinn]

Thanks Mike. The coils self supporting air core coils that are part of a Helmholtz design. I have some leeway on how the coil is designed. The only constraint is the ID needs to be 12" and I have a set # of turns. As such, I can modify the OD and the height of the coil to get my turns in.

I will continue to research variations on these two dimensions to see how the field changes at the axial center. If you have any additional input as to how the field could be maximized, either using a thinner coil (larger OD) or thinner coil (smaller OD), I would greatly appreciate it.

 

[MJR2]

The shorter the coil the better off you will be for a fixed NI.
Your basic equation is

NI=B*g*2.0195

B=gauss
g=airgap or height of your coil in inches

This is for a closed system. An open coil is much less efficient.

If you can do it wrap the coil in low carbon steel. Even if the gap is open.

You can figure a low field dipping into the bore similar to the radius of your ID. In other words you would want at least a 12" tall coil. Thiat is if you are not closed.

Mike