Discussion Forum

Hello,
We are working on design of 24 piece heaxapole permanent magnet halbach assembly. The magnets used here are VACODYM655HR with Br of 1.28 T (Hcj 1830 kA/m). The pieces on the assembly at 0 degree, 60 degree experience little demagnetization at the outer edges and the magnets assembled at 30 degree and corresponding 5 more position around the circumference experience very high demagnetisation in the inner side of the magnets. The demagnetisation is as high as -1200 kA/m on these magnets. So in order to avoid the risk of demagnetization, it is planned to use high coercive magnets such as VACODYM677HR with Br=1.28T (Hcj=2465 kA/m). Our aim is to get as high as possible magnetic field inside the bore of the magnet assembly.

Similarly we would like to use smaller pieces of magnets with high coercivity in places where higher demagnetising field exists.

We have used B=uourH+Br constitutive relation where the Br value with different magnetisation direction has been input. say Bx=Br*cos(theta) where theta is the direction of magnetisation similarly By is calculated too. please find the mph file attached for your reference. See the magnetic field distribution taken across the slice at half the height of the magnet. The blue shaded area where the demagnetising force is high and these are the places where we wish to use magnets with high coercivity.

Questions are:

1. How to input the data of Hcj in the simulation? We have both COMSOL 5 and 5.1. Can any one kindly help us in simulating with different Br and Hcj?

2. Can we use B-H curve in this type of simulation? where to input the B-H curve data?

3. how to use u0(H+M) constitutive relation?

4. There is an example of permanent magnet simulation ( U shape magnet) where the u0(H+M) relation is used. Can we use remnant flux density relation in this example and get the same results?

I request to you to kindly help in solving the above problem.
With kind regards,
Dr Ranjini Menon.