RE: [femm] (unknown)

If you integrate B over one half of your coil area and divide the result by the area, you get the average flux density. The x-direction in your model is 0.386T, not the 0.45T you used in your calculation.

Also with femm being a 2-d FE package, you cannot count the wire in your coil that runs in the x direction, only the lengh of wire that is perpendicular to the plane of the model can be counted. This makes your effective coil length 14mm, not 22mm.

So from your model, using the measured coil area of 1.701e-5m^2, and the average flux denisty of 0.386T and the current density of 1.176A/mm^2, the force becomes1.701e-5m^2 * 1.176e6A/m^2 * 2*0.007m = 0.108N (the same as the Lorenz force calc, since we have effectively done just that)

Your calculation can be redone like this;

=0.1A * 14e-3 * 200 * 0.386 = 0.108N

-----Original Message-----
From: bhaskar bollapragada [mailto:bhaskar_77@xxxxxxxxxxx]
Sent: 28 January 2003 10:23
To: femm@xxxxxxxxxxxxxxx
Subject: [femm] (unknown)

Dear Mr.David Meeker,

I tried to model a linear actuator based on lorentz law principle. I have done the simulation without current in the coil and plotted the flux density in perpendicular direction between the magnet and the coil air gap. The flux density is around 0.45T.I took thisvalue and calculated the force experienced by the coil theoritically which is given by F=ILB

= 0.1A*22*10e-3 m*200*0.45T

the coil taken is with 200 turns and the length of the coil is 22mm as the depth of the yoke on which the coil is wound around is 7mm amd breadth is 4mm.

so I get a force of around 0.2N .

I simualted with current density of 1.176A/mm²(as the cross section of the coil designed is 17mm²) and calculated the force experienced by the coil using block integrals loretz force option and multiplied the obtained result with 7mm(which is the depth of coil) but I am getting the force as 0.1N.The difference is almost 50% where I have gone wrong can you suggest.I am sending the femm file as attachment.

thanking you,

your's faithfully,

Bhaskar Bollapragada

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