## Magnet shape with respect to calculating intrinsic flux density

## Magnet shape with respect to calculating intrinsic flux density

(OP)

Excerpt from LakeShore Measuring Permanent Magnet Characteristics with a Fluxmeter and Helmholtz Coil

"Deriving Intrinsic Flux Density

The magnetic moment of interest in permanent magnet testing is generally

defined as the intrinsic flux density per unit volume of magnet. Based on the

magnetic moment measurement and measured magnet volume, intrinsic

flux density, Bdi, can be calculated.

Moment/Volume"

How does the shape of the magnet influence this "Volume", or does it (arc segment, square or rectangular, cylinder, etc.) And if it does, how is this accounted for?

"Deriving Intrinsic Flux Density

The magnetic moment of interest in permanent magnet testing is generally

defined as the intrinsic flux density per unit volume of magnet. Based on the

magnetic moment measurement and measured magnet volume, intrinsic

flux density, Bdi, can be calculated.

Moment/Volume"

How does the shape of the magnet influence this "Volume", or does it (arc segment, square or rectangular, cylinder, etc.) And if it does, how is this accounted for?

Clyde Hancock

Design & analysis of electric motors and generators

www.motorconsultants.com

## RE: Magnet shape with respect to calculating intrinsic flux density

The higher the L/D, the higher the Bd. if you use a hysteresisgraph in which case is a close circuit, L/D is infinite, and Bd=Br, and now you are measuring the intrinsic material properties, nothing to do with shape.

## RE: Magnet shape with respect to calculating intrinsic flux density

Clyde Hancock

Design & analysis of electric motors and generators

www.motorconsultants.com

## RE: Magnet shape with respect to calculating intrinsic flux density

Clyde Hancock

Design & analysis of electric motors and generators

www.motorconsultants.com

## RE: Magnet shape with respect to calculating intrinsic flux density

If you are working with a high Hc alloy then the Bd will actually be fairly close to Br.

For non-symmetrical shapes (arcs with radial mag) you really need to test in a fixture.

Typically, these would have pole pieces that match the magnet geometry. Then someplace in the return path of the steel there will be a controlled air gap with a Hall Effect probe in it to measure the flux. Changing the air gap changes the operating slope of the magnet.

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P.E. Metallurgy, consulting work welcomed

## RE: Magnet shape with respect to calculating intrinsic flux density

2. L/D for a rect is easy, convert area to equivalent diameter and divide by L. For an arc it becomes a series of approximations.

Start with the area at the mid-radius.

With any non-round shape the longer and narrower they are the more they will not exactly behave as expected. This is because the self demagnetization at the far corners will be greater than average for the magnet.

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P.E. Metallurgy, consulting work welcomed

## RE: Magnet shape with respect to calculating intrinsic flux density

there are three kinds of B-H curves: normal curve, intrinsic curve, operating/load curve. vendor data is normally based on intrinsic curve.

HHC tests Bdi, not Bd. Bd is proportion to L/D. At (BH)m point, Bd is normally much smaller than Br regardless of Hc (I bet Ed Stainless meant Bdi, NOT Bd, is close to Br when Hc is high)

L/D is an approximation itself. if the magnet does not have a constant cross-section, it is almost meaningless to estimate permeance coefficient based on L/D. Note B=flux/S, small area section will have higher B....

## RE: Magnet shape with respect to calculating intrinsic flux density

Clyde Hancock

Design & analysis of electric motors and generators

www.motorconsultants.com

## RE: Magnet shape with respect to calculating intrinsic flux density

= = = = = = = = = = = = = = = = = = = =

P.E. Metallurgy, consulting work welcomed

## RE: Magnet shape with respect to calculating intrinsic flux density