B Field of Large Ring Magnet Calculation

AI Thread Summary
The discussion revolves around calculating the magnetic field of a large Neodymium N35 ring magnet, where the user encounters a negative result of -15.0893364057539 Gauss. The parameters provided include remanence field, distance from the pole face, and dimensions of the ring. Participants suggest checking the calculation method for errors and note that the center of the ring has low field flux, which could explain the unexpected negative value. The user is exploring alternative methods, such as using a block magnet formula, and seeks a function specifically for surface ring magnet strength. Accurate calculations and understanding of magnetic field behavior are emphasized as crucial for resolving the issue.
jok
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Hi Everyone ,

Can anyone explain why I am getting negative result with a large Neodymium N35 ring Magnet ?

Br: Remanence field, independent of the magnet's geometry
z: Distance from a pole face on the symmetry axis
D: Thickness (or height) of the ring
Ra: Outside radius of the ring
Ri: Inside radius of the ring

Br: 12,300
z: 5mm
D: 10mm
Ra: 360mm
Ri: 330mm

(12000÷2)×((10+5)÷(SQRT((POWER(360,2)+POWER((10+5),2))))−(5)÷(SQRT((POWER(360,2)+POWER((5),2))))−((10+5)÷(SQRT((POWER(330,2)+POWER((10+5),2))))−(5)÷(SQRT((POWER(330,2)+POWER((5),2))))))

I am getting a result of : -15.0893364057539 Gauss .

Does it make sense for such a large magnet ?

Thank you

Screen_Shot_2015_08_17_at_10_15_33_AM.png
 
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Welcome to the PF.

I'd suggest doing it with a calculator and writing down the value of each term individually. Then see if you can spot the error in your (Excel?) formula calculation above.
 
berkeman said:
Welcome to the PF.

I'd suggest doing it with a calculator and writing down the value of each term individually. Then see if you can spot the error in your (Excel?) formula calculation above.

I did.

The results are correct .

Some said it is due to the fact that in the center of the ring there is very little field flux, which make sense . The center Z axis is very much away from the actual magnet.

So far what I came up with is using a block magnet formula to calculate a ring magnet by converting it to liner from circular .

But if there is a function for surface ring magnet strength. it would be very helpful.

Thank you
 
Hi, how did you get your value for z? I'm new to this and trying to work a similar problem, any help would be much appreciated
 

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