estimate axial field for disc shaped perm magn

[opster]

I need a rough idea of the field strength and gradient as a function of axial distance for a disk shaped perm magnet. I found a formula on the internet (

http://www.magnetsales.com/Design/DesignG.htm)

that I don't think is right. Shouldn't the formula be corrected for the demagnetizing field ( Br*(1-Nd), where Br is the remanence and Nd the demagnetizing factor )?

I need to produce a 1Newton force at a distance of 4cm on an iron or permanent magnet object with a volume of 1.57*10^-8 meters^3. I would like the field source to be as small in size as possible. The field source should be less than a pound in weight. I don't think it's going to be possible. The formula I'm using for the force is F = J*Volume*(dH/dx), where J is the polarization of the particle, and dH/dx is the field gradient.

Thanks for any suggestions

 

[MagMike]

The formula does not need correction. The shape demagnetization factor is already considered in the permeance coefficient (which are used in the formulas for calculating external flux).

Your force requirements are quite challenging, particularly the 4cm distance specification. The formular for force you are using is correct, but FEA would be more useful to determine if it is possible. Even then it would take some time to calculate.

Are you looking for just one magnet or many? I suggest you contact a vendor of permanent magnets to see if they can help you.

 

[nbucska]

your "iron or permanent magnet" is about equivalent to a 1500 ft cube and about 2.5 billion pounds-- unless you misplaced a decimal point... and one N will not be too effective to move an asteroid.

Most of the field is concemtrated in the vicinity of
the source magnet so I think about one ft is the maximum
what you have to take into consideration

Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>

 

[MagMike]

Hello nbucksa:
The OP's stated the volume is 10e-8 (not 10e+8) cubic meters. Admittedly, the minus sign on the exponent blends in with the ^ symbol.

 

[nbucska]

Sorry, I haven't seen it but this gives about 2.5 mm cube
which will be saturated when you reach a small fraction
of 1 N force -- so back to the drawing board.



Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>