SIMSCAPE permanent magnet example understanding

I have some newbie questions about understanding basic functionalities of 3 basic magnetic blocks presented at "permanent magnet attached to iron wall" example at

mathworks.com/help/simscape/ug/permanent-magnet-on-wall.html

1) Permanent magnet block

Cross-sectional area and Length of magnet - those two I get, those are dimensions of magnet .

Remanent flux density and Coercivity of Magnet: those two depend on magnet material and nor magnet dimensions right? They are from BH curve.

2) Reluctant force Actuator block

Does this represents the air between magnet and metal plate, so how far is the magnet from the metal plate? With relative permeability =1 being value for air.

- Initial/minimum air gap - this is the initial/minimum distance of magnet from the plate, so even if it is called "attached" in this example the value is set to 1e-3 (cant set to 0) so it is in fact magnet put "1mm far from metal plate without ability to get closer"?

- cross-sectional area - i suppose i have to recalculate and change this value according to dimensions set in permanent magnet block?

3)Material's reluctance force block

This is the block that represents the metal plate? But in the example the "Relative magnetic permeability of material" is set to 1,05, which, accroding to wikipedia, is value for Neodymium magnet and for Iron the value is 5000.https://en.wikipedia.org/wiki/Permeability_(electromagnetism)

"thickness or length of section or gap" and "Cross-sectional area" are the dimensions of given plate?

Answer 1

[Kothuri]

Hi @Simon,

• The "material properties" of the magnet i.e, Remanent flux density and Coercive field strength come directly from the magnet’s BH‐curve (datasheet given by manufacturer). And can be considered intrinsic to the chosen magnet grade, regardless of its dimensions.
• The "Reluctance Force Actuator" block closes the magnetic path from the permanent magnet into an air gap and thereby models exactly the small air gap of 1mm as a contact at exactly 0 m cannot be simulated as it would imply infinite flux or zero reluctance and it also calculates the mechanical force on the magnet due to that gap.
• By setting Relative premeability to 1, this block is effectively modeling "pure air" in that gap.
• The cross‐sectional area of this block should match the face‐area the magnet is presenting to that gap.
• The "Material's reluctance force" block models a piece of ferromagnetic material which is a iron wall in the entioned example.
• In the example they used "Relative magnetic permeability of material" as 1.05 only to show some flux drop inside the “wall,” but that is not the actual permeability of iron.
• If "Relative magnetic permeability of material" is set as 5000 for simulating a realistic iron wall, then the wall’s reluctance becomes very small compared to the air gap.and almost all the magnetic “drop” happens in the air gap.
• "thickness or length of section or gap" is the thickness of the steel the flux must cross.
• "Cross-sectional area" is usually the same as the magnet face.

You can refer the below documentation links for more info on:

• Permanent magnet block- https://www.mathworks.com/help/simscape/ref/permanentmagnet.html
• Reluctance force actuator block- https://www.mathworks.com/help/simscape/ref/reluctanceforceactuator.html
• Reluctance block- https://www.mathworks.com/help/simscape/ref/reluctance.html