New Gitec article on AlNiCo magnets

[antigua]

The German guitar group called Gitec, who focus on physics and other scientific principles of electric guitars, as just posted another scientific article on AlNiCo magnets gitec-forum.de/wp/wp-content/uploads/2017/12/Z35E_Alnico-Magnets.pdf



The focus of this article is mostly about how the degaussing of AlNiCo pole pieces (as opposed to bar under mount magnets) effects the electrical properties of a pickup. Their finding is that when AlNiCo pole pieces lose magnetism, the inductance of the pickup drops slightly, as well as increasing the resonant peak slightly. AlNiCo 5 doesn't this more prominently than AlNiCo 2. Degaussed AlNiCo 5 also shows a slightly higher Q factor as well, whereas degaussed AlNiCo 2 causes it to change very little. These differences are probably too small to be heard, but it's interesting to know that they occur. If the differences could be heard, it would mean that weakened AlNiCo would produce a brighter sound, more so with AlNiCo 5 than AlNiCo 2.



Given that the difference is small, you might be wondering "so what?", well with all the unsourced claims that are made about what magnets can and can't do for a guitar pickup, there's almost as much value in knowing what doesn't happen as there is what does. It's also worth noting that decreasing gauss strength of pole pieces changes how the pickup pulls against the strings, and that makes for a difference, though it is a physical difference as opposed to an electrical one, and is approximately the same as raising or lowering pickups.



Gitec has been posting research for years in the German language. They have recently been translating a lot of their work into English gitec-forum.de/wp/en/ , so if you like science and you like guitars, check out their other work as well.

[Deleted]

I just navigated to their knowledge base, entered "sustain" -> search, I got no matches found.

[antigua]

I'm surprised that they found any electrical difference at all between charged and uncharged states. I wouldn't think the Br value of the AlNiCo would have any effect on its permeability, and I especially don't understand why it would effect the conductivity of the AlNiCo, hence effect the Q factor. 

[ms]

Changes in permeability with the degree of magnetization are expected.  This can be understood by studying the hysteresis curve.

[antigua]

Dec 9, 2017 6:04:50 GMT -5 ms said:

Changes in permeability with the degree of magnetization are expected.  This can be understood by studying the hysteresis curve.

Thanks for dropping in. Is the degree of difference in permeability in any way proportionate to the difference between BHmax and Br?

This other text from GITEC shows BH curves for AlNiCo 2,3 and 5 gitec-forum.de/wp/wp-content/uploads/2017/12/PotEG-4.4.1-Alnico-Magnets.pdf , with AlNiCo 5 having a rounded curve, where as AlNiCo 5 has a harder knee in the curve. We know that the AlNiCo 2 and 3 have a higher permeability than AlNiCo 5, thereby increasing the inductance of the pickups they're in, is that reflected in the fact that the BH curves of AlNiCo 2 and 3 are softer curved than AlNiCo 5? 

What about the change in Q factor? Any idea why the formation of eddy currents would be impacted, and impacted more so in AlNiCo 5?

[ms]

Dec 9, 2017 16:04:05 GMT -5 antigua said:

Dec 9, 2017 6:04:50 GMT -5 ms said:

Changes in permeability with the degree of magnetization are expected.  This can be understood by studying the hysteresis curve.

Thanks for dropping in. Is the degree of difference in permeability in any way proportionate to the difference between BHmax and Br?

This other text from GITEC shows BH curves for AlNiCo 2,3 and 5 gitec-forum.de/wp/wp-content/uploads/2017/12/PotEG-4.4.1-Alnico-Magnets.pdf , with AlNiCo 5 having a rounded curve, where as AlNiCo 5 has a harder knee in the curve. We know that the AlNiCo 2 and 3 have a higher permeability than AlNiCo 5, thereby increasing the inductance of the pickups they're in, is that reflected in the fact that the BH curves of AlNiCo 2 and 3 are softer curved than AlNiCo 5? 

What about the change in Q factor? Any idea why the formation of eddy currents would be impacted, and impacted more so in AlNiCo 5?

Refer to the hysteresis curve here: www.nde-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/HysteresisLoop.htm.  We have the driving magnetic field on the horizontal axis and resulting B field on the vertical axis.  So when the magnetic medium is in some state represented by a point on the curve, you have some degree of magnetization as a result of some driving field.  But the curve also gives you information about how the magnetization changes as a result of small changes in the driving force.  For example, at the extreme right or left parts of the curve, it is horizontal.  That is, increasing the applied magnetic force (or field) results in no more magnetization.  This is saturation: the medium can give you nothing more.  So it makes sense to think of the slope of the curve as telling you how much the medium can respond for a given change in magnetic forcing (or applied field).  This slope is proportional to the permeability. So the permeability tells you how much the medium can respond to a small change in applied field beginning from some point of the curve. Since the slope of the curve varies depending on where you are on the curve, the permeability is variable.

The eddy currents that flow depend on  more than the conductivity; they depend also on how much of the medium is involved in carrying the current.  This is controlled by the skin effect, and the depth of current flow depends on both the conductivity and the permeability.  Thus changing the permeability can alter the losses in the medium.

[antigua]

Dec 10, 2017 7:08:42 GMT -5 ms said:

Dec 9, 2017 16:04:05 GMT -5 antigua said:

Thanks for dropping in. Is the degree of difference in permeability in any way proportionate to the difference between BHmax and Br?

This other text from GITEC shows BH curves for AlNiCo 2,3 and 5 gitec-forum.de/wp/wp-content/uploads/2017/12/PotEG-4.4.1-Alnico-Magnets.pdf , with AlNiCo 5 having a rounded curve, where as AlNiCo 5 has a harder knee in the curve. We know that the AlNiCo 2 and 3 have a higher permeability than AlNiCo 5, thereby increasing the inductance of the pickups they're in, is that reflected in the fact that the BH curves of AlNiCo 2 and 3 are softer curved than AlNiCo 5? 

What about the change in Q factor? Any idea why the formation of eddy currents would be impacted, and impacted more so in AlNiCo 5?

Refer to the hysteresis curve here: www.nde-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/HysteresisLoop.htm.  We have the driving magnetic field on the horizontal axis and resulting B field on the vertical axis.  So when the magnetic medium is in some state represented by a point on the curve, you have some degree of magnetization as a result of some driving field.  But the curve also gives you information about how the magnetization changes as a result of small changes in the driving force.  For example, at the extreme right or left parts of the curve, it is horizontal.  That is, increasing the applied magnetic force (or field) results in no more magnetization.  This is saturation: the medium can give you nothing more.  So it makes sense to think of the slope of the curve as telling you how much the medium can respond for a given change in magnetic forcing (or applied field).  This slope is proportional to the permeability. So the permeability tells you how much the medium can respond to a small change in applied field beginning from some point of the curve. Since the slope of the curve varies depending on where you are on the curve, the permeability is variable.

The eddy currents that flow depend on  more than the conductivity; they depend also on how much of the medium is involved in carrying the current.  This is controlled by the skin effect, and the depth of current flow depends on both the conductivity and the permeability.  Thus changing the permeability can alter the losses in the medium.

The thing about the BH curve though is that it depicts conditions that don't happen in a guitar pickup, where the magnet is is in state of retentivity, with tiny H fields applied. I found a section of the Manfred Zollner's book that addresses this though gitec-forum.de/wp/wp-content/uploads/2017/12/PotEG-4.3-Matter-in-Magnetic-Fields.pdf   I think the situation at hand is described more by that little leaf-like curve at "p" in the graph to the right, but it would be centered over the axis since there H field is small and alternating. Is it possible to predict the smaller "p" curve, based on an ordinary BH curve which doesn't include this?

[ms]

Dec 10, 2017 13:06:40 GMT -5 antigua said:

Dec 10, 2017 7:08:42 GMT -5 ms said:

Refer to the hysteresis curve here: www.nde-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/HysteresisLoop.htm.  We have the driving...

The thing about the BH curve though is that it depicts conditions that don't happen in a guitar pickup, where the magnet is is in state of retentivity, with tiny H fields applied.

It explains how the permeability can be different if the magnet is magnetized to a greater or lesser degree.  The slopes of the curves of points b and e in figure 4.6 are not the same.