How to Perform Load Line Analysis for Loudspeaker Drivers in FEMM 4.2?

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SUMMARY

This discussion focuses on performing load-line analysis for loudspeaker driver magnetic circuits using FEMM 4.2. The permeance coefficient (Pc) is calculated using the formula Pc = (B.M)/(µ0*H.M), where B and H are vector quantities representing magnetic flux density and magnetic field, respectively. The confusion arises from interpreting the reported values of B and H, particularly when the "Demag H in PMs" option is enabled. Participants also discuss whether Bd and Hd must lie on the BH curve, highlighting the complexities of magnetic circuit modeling.

PREREQUISITES
  • Understanding of magnetic circuit theory
  • Familiarity with FEMM 4.2 software
  • Knowledge of vector mathematics, specifically dot products
  • Basic concepts of magnetic materials and their properties
NEXT STEPS
  • Research the calculation of permeance coefficients in magnetic circuits
  • Explore the implications of the "Demag H in PMs" setting in FEMM 4.2
  • Study the relationship between magnetic flux density (B) and magnetic field (H) on the BH curve
  • Investigate load-line analysis techniques for piezoelectric materials
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Engineers and researchers involved in loudspeaker design, magnetic circuit analysis, and those utilizing FEMM 4.2 for electromagnetic simulations.

flowwolf
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Dear Forumers,

This question is about load-line analysis for loudspeaker driver magnetic circuits in FEMM 4.2 (Finite Element Method for Magnetics), I can't seem to get an answer from the mailing lists.

I would like to get the permeance coefficient for random points inside the magnet.
I have problems interpreting the results reported by femm.
Most information sources tell me that pc = Bd/Hd, but B and H are vector quantities,
and I'm not sure which parts to use (either |B|,|H| or the components).

According to a JMAG newsletter I've read, Pc = - Bd / (µ0 Hd), where
"Bd [T], Hd [A/m]: The projection components in the magnetizing direction M of the magnetic flux density B and magnetic field H"

So does that mean that pc = Bz / Hz, if the magnetization direction is 90 degrees?I saw old mails about the permeance coefficient as well: http://www.femm.info/list/msg01827.html
where it was stated that Hd = H - Hc (if the "Demag. H in PMs" option is not set)

But subtracting Hc from |H| does not result in the |H| that is reported when "Demag. H in PMs" is setAll these confuses me, could I get some help about which values to use?

Also do Bd and Hd necessarily have to fall on the BH curve, or is the load-line given by
the intersection of a line with steepness of pc, where Bd and Hd are not necessarily on the BH curve?Any help would by appreciated.

Akos
 
Are the magnetic materials isotropic (same in every direction)? If so the B and H vectors are in the same direction and I would think the magnitudes would be the natural choice. About the load line problem, I'd like to know more about it as I have similar modeling issues with piezoelectric materials. I too find it confusing.
 
Hello Paul,
I've received an answer from David Meeker:
"For your case, on a point-by-point basis, you'd want to compute:
Pc = (B.M)/(µ0*H.M)
where B is the reported B for a point inside a PM, H is the reported H for a point in the PM (with the default (checked) "Demag H in PMs" setting), and M is the magnetization in the block. Note that B, H, and M are all vectors, and . represents the dot product."

He pointed me to http://www.femm.info/Archives/misc/BarMagnet.pdf
 
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Likes   Reactions: Paul Colby
Very helpful, thanks. I once analyzed a variable reluctance motor using magnetic circuit theory. The parallel with piezoelectric materials should be understandable.