## Homogeneity of magnetic flux and rotational eddy losses

## Homogeneity of magnetic flux and rotational eddy losses

(OP)

Hi:

I am building an application were a Disc magnet is placed closed to a copper plate. This magnet rotates about its axis. This magnet will not move with respect to the plate, only rotate.

I want to minimize eddy current losses due to this rotating magnet but maximize eddy current losses by translation in any direction.

In principle if the magnetic flux is perfectly homogeneous on the surface, meaning that along a given circle of any radius on the surface of the cylinder the flux is the same along that circle. If also the magnetic flux axis is aligned with the axis of rotation, this rotation should not produce eddy currents.

How accurate is my assumption?

Are magnets in real life this homogeneous?

Is the magnetic axis the same as the geometric axis of the magnet?

Is there a way to minimize rotational eddy currents without minimizing transnational eddy currents?

I am planning to enclose the magnet as much as possible with non/ferrous materials to maximize this transnational damping.

My final goal is to have a magnet/plate setup in which the magnet can rotate as free as possible along its magnetic axis, but be damped as much as possible by any translation movement.

Very similar to a magnetic bearing.

Thanks

Fernando

I am building an application were a Disc magnet is placed closed to a copper plate. This magnet rotates about its axis. This magnet will not move with respect to the plate, only rotate.

I want to minimize eddy current losses due to this rotating magnet but maximize eddy current losses by translation in any direction.

In principle if the magnetic flux is perfectly homogeneous on the surface, meaning that along a given circle of any radius on the surface of the cylinder the flux is the same along that circle. If also the magnetic flux axis is aligned with the axis of rotation, this rotation should not produce eddy currents.

How accurate is my assumption?

Are magnets in real life this homogeneous?

Is the magnetic axis the same as the geometric axis of the magnet?

Is there a way to minimize rotational eddy currents without minimizing transnational eddy currents?

I am planning to enclose the magnet as much as possible with non/ferrous materials to maximize this transnational damping.

My final goal is to have a magnet/plate setup in which the magnet can rotate as free as possible along its magnetic axis, but be damped as much as possible by any translation movement.

Very similar to a magnetic bearing.

Thanks

Fernando

## RE: Homogeneity of magnetic flux and rotational eddy losses

Practical axially magnetized magnets should be quite homogeneous in field strength and direction about their axis.

The magnetic axis can be unrelated to the physical axis--you want an axially magnetized magnet for their axies to be coincident.

A single pole axially magnetized disc magnet will minimize rotational eddy currents.

Increasing pole count

concentricallywill increase translational eddy currents, to a point--the pole width should be less than the air gap.## RE: Homogeneity of magnetic flux and rotational eddy losses

"This magnet will not move with respect to the plate, only rotate.

maximize eddy current losses by translation in any direction

be damped as much as possible by any translation movement"

If the magnet does not move with respect to the plate, how do you get any translational losses/damping?

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## RE: Homogeneity of magnetic flux and rotational eddy losses

## RE: Homogeneity of magnetic flux and rotational eddy losses

Concerning the translation, you should have the disc magnet smaller in diameter wrt the copper plate, so that there is a field change when moving, but once again you won't experience a large damping and it depends also on the amplitude of the lateral movement you want to stop.

prex

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## RE: Homogeneity of magnetic flux and rotational eddy losses

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