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Old 17th September 2010, 08:21 PM   #11
WrineX is offline WrineX  Netherlands
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oh i just checked another femm sim an it looks like the last picture as you mentioned degrees on 0 is in fact the right one i just thought i looked odd beacause most of the flux is on top and bottom. and i see the flux is with e001 etc so light green is 0.3 Tesla instead of 3.1313 etc stupid me
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Old 17th September 2010, 08:49 PM   #12
WrineX is offline WrineX  Netherlands
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there is only one questioin left importend for me before i gone try loads of magnets i see many people use femm but isnt it true it can only let you see 2d, i now i used square magnets or at least they are the same width and expecially depth. (from top view) what does femm do when you had a magnet of 40x10x5, because he only knows 2 sizes of them prob the 40x10 what about the 5 mm ? does he makes his calculation based on 40x10x10 ? or what. also whast the influance of different size ratio's of the magnets ? like real thin but width and long or what ever.
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Old 17th September 2010, 09:27 PM   #13
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This simple FEMM ribbon tweeter layout may help you see how the N-S and N-S magnetic directions are used to create the ribbon gap flux.

This front view shows the total flux energy in the gap over the total magnet depth, and not just the center-gap flux an aluminum ribbon would experience. When you look at a front view simulation you need to apply a distribution function to the total flux energy show in the simulation to get just the central gap flux the ribbon will experience.

Hence, several 2D top view cross section simulations are often run to estimate the actual gap flux vector the ribbon will experience. The cross section shown would represent a top/bottom section where a cross brace is added to complete the magnetic circuit. The square steel path between the N-S pole steel is a crude way to model a 3D cross brace in a 2D view. Alloys like permalloy could be used to carry the magnet flux with minimal loss to the actual steel cross brace.
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File Type: jpg Ribbon_Top_Crossection.jpg (30.6 KB, 63 views)
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Old 17th September 2010, 09:36 PM   #14
WrineX is offline WrineX  Netherlands
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ok so the Alloy like permalloy is used to make a top view , and still have the crossbar like in the front view? or you mean people really ad that crossbar as seen in you second picture, because if i understand you right its just to compensate for the one that is in the front view as well.


and this distribution factor can you tell me mroe about that >? or shall i just use the top view to exactly see whats going with the flux where the ribbon should be.

funny i just made such topview to compare it with the front view and indeed noticed that the flux in the middle between the magnets where ribbon sits whas really much lower then the fronview indicated.

if i missed something pls tell
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Old 17th September 2010, 10:02 PM   #15
WrineX is offline WrineX  Netherlands
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ok i tried something with the top view.

1 picture is front view
2 is top and added te otherwise lost crossbarr at the back, this i dont know if this is legal or not. but without it is the result in picture 3 ans is clearly diferent. and in the front view there is ofcourse also a piece of steel that connects the 2 poles so.
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