# Help with Magnetic Dipole Moment

1. Jul 14, 2016

### Nash Engineer

Im looking to find the resultant magnetic moment of a permanent magnet inside of a steel housing. Some of the remnant flux density is absorbed by the magnet and the field is altered. I want to figure out the total magnetic dipole including the presence of the steel housing. I've been using Comsol but I am new to that program and I am unsure of how to work the formulas

2. Jul 17, 2016

### marcusl

Magnetic fields in the presence of iron are not readily soluble analytically, so numerical modeling is the right way to go. I don't understand what you mean by "how to work the formulas." Have you taken an advanced undergrad E&M class? You'll see how magnetization, magnetic induction and magnetic fields are related, and how a ferromagnetic material doesn't "absorb" flux but rather reroutes it (the relevant properties are permeability and reluctance). I'm not familiar with Comsol but would be surprised if it requires formulas--don't you mesh up your geometry and solve it with finite elements or some similar technique?

3. Jul 18, 2016

### Nash Engineer

Well, I'm a mechanical engineer but this is part of a project I have to do. Yes I am just meshing it in comsol. I am then using the the software to calculate magnetization of the entire volume. What I am confused about is that when I have the permanent magnet alone I get the correct Magnetic moment, however when I add the steel housing around the Magnet I get higher Magnetic Moment which doesn't make sense. If I want to find the magnetic moment to simplify this assembly into its equivalent singular magnet to use in another more complex model I think I should expect the Magnetic moment to drop a little with the addition of the steel housing.

4. Jul 18, 2016

### Nash Engineer

Can I expect the magnetic moment that's routed through the steel to take away from the effective magnetic moment in this case?

5. Jul 18, 2016

### marcusl

Agreed, moment shouldn't look bigger. Without knowing details of your problem, geometry, etc., it's impossible to know where you went wrong. Simulation codes can be tricky, especially regarding meshing and boundary conditions. The best approach would be to sit down with someone experienced in COMSOL who can review your model and assumptions. A couple of other questions they can address: How do you know that the dipole moment of the permanent magnet is "correct"? Why do you assume that your larger system will be accurately modeled if you replace a complex geometry by a simple dipole?

Sorry, this is not the sort of problem that I could diagnose over internet even if I were familiar with COMSOL.