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hylander4 is offline
Jun8-11, 02:16 PM
P: 27
1. The problem statement, all variables and given/known data

An infinite cylindrical shell of radius b is placed inside a constant field B which points along the upwards z-axis. A second cylindrical shell of radius a<b is placed inside the first cylindrical shell, and the volume from b>r>a is filled with a paramagnetic material of permeability u. Find the magnetic field everywhere.

2. Relevant equations

H = B/(u_0) + M

H = -grad W

Laplacian W = -grad M

W is continuous over all boundaries.
The change in dW/dr over a boundary is equal to the negative change in Magnetization over the boundary.

Cylindrical laplace equation solution (From my undergraduate E+M notebook)

W(r, phi) = D_0 + A_0*(a+b*phi) +
$\EPSILON$ [r^n + (A_n*r^-n)]*[B_n*cos(n*phi)+C_n*sin(n*phi)]

Another version of this equation can be found here on page two.

Summed from n = 1 to infinity

3. The attempt at a solution

Since there's no free current in this situation, I tried using magnetic scalar potential to solve this problem. Unfortunately, I end up with too many variable in the proposed Laplace equation solutions that I need to create to use the boundary conditions.

In my main attempt I had four boundary conditions and seven types of variables.

My main problem is that I need to find the H field to find the B-field, but in order to find the H-field, I also need a function for the paramagnetic material's Magnetization density M.

The forum wants me to post my attempts, but I've already filled three pages of notebook paper with failed algebra and I doubt that that would be constructive. I'm not really looking for an exact solution, I really just need general guidance.
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