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Old 17th February 2015, 06:12 PM   #1
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Default How to optimize Magnet structure?

I am building a driver with a linear voice coil (VC) and it works but I would like to optimize the magnetic motor design to increase efficiency and reduce distortions. Here is a sketch of a design (there is a mirror assembly for the return VC):
A and B are Neodymium magnets. Either one could be replaced by steel (1018). Is there any benefit of having both magnets? Magnet B will be close to the VC and maybe needs to be a more temperature resistant version (SH).
Any other suggestion?
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Old 17th February 2015, 10:13 PM   #2
solhaga is offline solhaga  Sweden
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Two things about having the Neo that close to the VC:

Non-linearity of the flux in the gap; make a FEMM simulation and find out.

Heat dissipation making the Neo non-magnetic; most Neo can only withstand 80 degrees Celsius.
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Old 18th February 2015, 12:02 AM   #3
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What is the purpose of this design linear voice coil means nothing as far as I am aware as there is no such thing as a curved voice coil. Depending on what you are trying to achieve will change my answer. Also the only way to truly know is to do a FEMM model. fairly simple to do. I would recommend a different app to design it and then Femm to model it. I would be happy to assist were I can but I am no expert by any means.
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Old 18th February 2015, 12:20 AM   #4
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Quote:
Originally Posted by solhaga View Post
Two things about having the Neo that close to the VC:

Non-linearity of the flux in the gap; make a FEMM simulation and find out.

Heat dissipation making the Neo non-magnetic; most Neo can only withstand 80 degrees Celsius.
There are grades like N42SH or N45SH which are surviving 150ºC but they cost more and are mostly special order items.
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Old 18th February 2015, 12:22 AM   #5
sreten is offline sreten  United Kingdom
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Hi, Search on Linaeum for clever linear voice coils, rgds, sreten.
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Old 18th February 2015, 12:42 AM   #6
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The only practical improvement to having the magnets split up as shown is a reduction in profile compared to having it in only one spot, which would require more width. The addition of upper section poles (as per your drawing) also gives extra leakage paths and a corresponding reduction in useful gap flux. Running a typical hi-fi speaker with 2 layer coil to the point where the magnets or any part of the pole pieces goes beyond 50 C usually means the voice coil is bound to fail first and soon, and probably isn't the first thing you need to worry about in spite of the popularity of it. If your actual coil volume is Much higher in reality compared the drawing scale, maybe you should think about heat sinking. Simulations are cool if you can guarantee material characteristics, so if you run sims and want to rely on that performance, don't buy your steel from Lowes or Ebay.
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Old 18th February 2015, 12:58 AM   #7
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Maybe I should describe what I want to achieve is a narrow rectangular voice coil. Sibatech makes something similar Anybody tried FAL drivers? but I want to make it much more narrow, may be no gap between the right and left side of the structure(i.e. one single center steel piece). So this version uses only what I call magnet A but other designs I found use only B like http://harman-kardon.cz/infinity/dat...ng-surface.pdf (but I would use onle a single voice coil).
One of the reasons to split the magnets is to allow a more narrow shape but I am not sure how much one would gain.

Last edited by Monteverdi; 18th February 2015 at 01:22 AM.
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Old 18th February 2015, 04:18 AM   #8
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Well I guess the only real answer is to go download femm And maybe some cad software and play around in it until you are satisfied. Besides the motor what are you trying to make?
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Old 18th February 2015, 06:06 AM   #9
solhaga is offline solhaga  Sweden
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I fiddled around with a linear motor recently when I tried to make a planar bass.
I did manage to build them but got stuck on the VC, it was hard to get the accuracy needed.
Some motors, although simulated very well in FEMM, just couldn't be built (well, not to last anyway) and some were in fact lethal.

BTW, FEMM can export DXF if you want the CAD work with it.
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Old 18th February 2015, 06:16 AM   #10
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Quote:
Originally Posted by solhaga View Post
I fiddled around with a linear motor recently when I tried to make a planar bass.
I did manage to build them but got stuck on the VC, it was hard to get the accuracy needed.
Some motors, although simulated very well in FEMM, just couldn't be built (well, not to last anyway) and some were in fact lethal.

BTW, FEMM can export DXF if you want the CAD work with it.
Did you mean Import? modeling in Femm I think is pretty clumsy but using a 2d modeler which is easy and then importing to Femm works very well. That is a very good point Solhaga Some things are theoretical but very impractical or even damn near impossible to build.
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