Short and long magnets
Here is the first simulation.
On the left, two 5x1.5 cm neodymium magnets. On the right, two 20x1.5 cm neodymium magnets. On the left, the predicted B is 0.47 T (tesla) for the ribbon gap. On the right, 0.18 T.
According to the simulation, there is strong decrease of the magnetic field in the ribbon gap.
Here is the first simulation.
On the left, two 5x1.5 cm neodymium magnets. On the right, two 20x1.5 cm neodymium magnets. On the left, the predicted B is 0.47 T (tesla) for the ribbon gap. On the right, 0.18 T.
According to the simulation, there is strong decrease of the magnetic field in the ribbon gap.
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Introducing a gap between magnets
On the right, two 5x1.5 cm neodymium magnets. On the left, eight 5 x1.5 cm neodymium magnets with a 1.0 cm gap between the magnets.
The 1cm gap is not enough large enough to get the same magnetic field as in the shorter system. Furthermore, the magnetic field drops near the gap (0.09 T)
On the right, two 5x1.5 cm neodymium magnets. On the left, eight 5 x1.5 cm neodymium magnets with a 1.0 cm gap between the magnets.
The 1cm gap is not enough large enough to get the same magnetic field as in the shorter system. Furthermore, the magnetic field drops near the gap (0.09 T)
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Filling the gaps with steel and adding two side bars
In this simulation, the gaps are filled with steel. Furthermore, two steel bars are placed on the side.
I also made a simulation with a gap of 1.5 cm long and another one with a gap of 5 cm. With 1.5 cm, the maximum B is 0.73 T. With 5 cm, the maximum B is 0.68 T.
As of know, I don't know what the optimal gap length could be.
On average, the magnetic field with steel gaps is much stronger than without gaps. Unfortunately, there are small areas where the magnetic field drops, near the junction magnet-steel.
Using gaps filled with steel could both improve the performance and decrease the cost of a ribbon driver.
I wrote "could", because it is only a simulation.
Now if I would have a steel saw ...
In this simulation, the gaps are filled with steel. Furthermore, two steel bars are placed on the side.
I also made a simulation with a gap of 1.5 cm long and another one with a gap of 5 cm. With 1.5 cm, the maximum B is 0.73 T. With 5 cm, the maximum B is 0.68 T.
As of know, I don't know what the optimal gap length could be.
On average, the magnetic field with steel gaps is much stronger than without gaps. Unfortunately, there are small areas where the magnetic field drops, near the junction magnet-steel.
Using gaps filled with steel could both improve the performance and decrease the cost of a ribbon driver.
I wrote "could", because it is only a simulation.
Now if I would have a steel saw ...
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Member
Joined 2003
Sorry, but I don't know how to perform such a rotation in FEMM. I could send you the FEMM file if you wish.
Hi brunob
Your sims shows a magnetsystem for a ribbon .The gab for the ribbon is only as wide as the thicknes of one of your magnets.Probably 15mm.
You can not see that the field strength goes both + and -
Sorry ,but i think i am right here.
I have been reading the simms wrong too,but i think i have got it right now
Bernt
Your sims shows a magnetsystem for a ribbon .The gab for the ribbon is only as wide as the thicknes of one of your magnets.Probably 15mm.
You can not see that the field strength goes both + and -
Sorry ,but i think i am right here.
I have been reading the simms wrong too,but i think i have got it right now
Bernt
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Member
Joined 2003
I think you are looking "into" the gap from front rather than looking down on section of gap from top. Orientation in FEMM would be the same as shown in post 577 by tinitus. Back polepiece would contact N pole on one magnet, S pole on the other magnet. Gap for ribbon would be at the other side of magnets (across N-S open space between magnets).
Hi brunob
Your sims shows a magnetsystem for a ribbon .The gab for the ribbon is only as wide as the thicknes of one of your magnets.Probably 15mm.
You can not see that the field strength goes both + and -
Sorry ,but i think i am right here.
I have been reading the simms wrong too,but i think i have got it right now
Bernt
The gab I used is indeed 15 mm large.
Could you explain how you generated your plot? Is it a simulation or a measurement?
I made two simulations. The one on the left represents the way I built my first ribbon. The one on the right is based on Tinitus post 577. The magnetic field is stronger on the left simulation. Also, for both cases, the sign of the magnetic field does not vary in the ribbon gap.
Note that these simulations have nothing to do with the previous simulations I described about leaving a space between the magnets (a few posts before this one).
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Hi bruno
Thats nice
Please note the iron on back
And the copper plates
Also note that one reason for doing it the way I suggest makes it possible to do a design with much less diffraction issues from magnets
Also a very important factor
Its not all about getting a stronger magnet system
Another advantage is that its possible to use exstremely strong flat and wide magnets, which are usually magnetized through the thickness
And you can use those bigger and much stronger magnets without compromising the acoustic aspects
Thats nice
Please note the iron on back
And the copper plates
Also note that one reason for doing it the way I suggest makes it possible to do a design with much less diffraction issues from magnets
Also a very important factor
Its not all about getting a stronger magnet system
Another advantage is that its possible to use exstremely strong flat and wide magnets, which are usually magnetized through the thickness
And you can use those bigger and much stronger magnets without compromising the acoustic aspects
Attachments
Member
Joined 2003
Both of these new models will work, but gap strength will be much higher in both models with one N-S combination connected by steel pole piece like tinitus suggests. Left side sim will be a little more difficult to build, but it can be done with multiple steel bars so you end up with "U" magnet with N-S poles facing each other.
Alternatively, you can get good gap strength in left model by using two steel pole pieces extending directly to left and right of magnets. These pole pieces help reduce magnetic "short circuit" in air.
Alternatively, you can get good gap strength in left model by using two steel pole pieces extending directly to left and right of magnets. These pole pieces help reduce magnetic "short circuit" in air.
Thanks for the explanation and the picture with labels.
In your design with the iron on back, you have a small cavity, which means resonances from the back wave. How are you going to handle this problem?
Bruno
No, its not really a dipole ribbon
I hope that felt will do the trick
But as said, with the ribbon in front of the magnets I expect less diffraction problems
Back to the gaps filled with steel.
In this FEMM simulation, I have a 20 cm long ribbon system without gaps on the left side of the 1st picture,
on the right side, another 20 cm long ribbon system with two 2.5 cm gaps filled with steel on each side.
The second picture shows a plot of the |B| along the Y axis in the middle of the ribbon gap (see red line on the 1st picture).
I am afraid that an irregular magnetic field would induce distortions.
Bruno
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... sorry but those simulations are correct, the field is perpendicular to the driving current direction!
Hey,
Do you have gaps at the left, but no steel?
What if you simulate the classic way to do it, with neo on steel, no gaps, all the way up?
What is your point having gaps?
I have done it that way, with a magnetic high at 185cm, and a gap between neo rails at 2,1 cm. There is no problem playing loud!
Cheers Jan Jensen
Do you have gaps at the left, but no steel?
What if you simulate the classic way to do it, with neo on steel, no gaps, all the way up?
What is your point having gaps?
I have done it that way, with a magnetic high at 185cm, and a gap between neo rails at 2,1 cm. There is no problem playing loud!
Cheers Jan Jensen
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Hello ,
how about attaching your unsolved *.FEM file to your next post so we can take a closer look on the subject?
You can even open the file directly with any texteditor and copy/paste the content here .
I am still very sceptical about introducing gaps as a solution to gain more flux , sounds too easy .
You should have noticed already that the ungapped variation to the left in your pic is completely wrong , it shows constant flux across the gap width , which is not possible physically without special treatment .
A simulation with 90deg rotated view looking from the top will show you a more realistic impression of the field distribution , stronger to the sides and weaker in the middle .
Doing so gives two different results with the same (limited) 2D FEA analysis program , which one is "correct" ??
Decide by yourself ...
thanks & bye
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