Meanwhile, i was trying to better visualize the magnetic field lines coming from the magnets / coils / cores, and i did this by using a compass to sniff out these field lines.
OMG! That was a lot of work. No iron powder, heh ?
Anyway, if you want such mappings to be precise in the future then the drawing plane should contain the axis of the device.
There is no field strength indication, just the position and direction of the field, but normally, the further away from the magnets or active coil, the weakest the field becomes.
That is an important piece of information, because flux density that is too low might be insufficient for small radii of the metal ring.
Flux density can be estimated from the H, dimensions and permeability, though, but an empirical measurement would be worth more.
I made 3 measurements, with the magnets only, with the active coil only and with both, in all 3 cases all the soft cores were present.
The coil was activated with 2.8A of current as that's what creates a roughly similar strong magnetic field compared with the 4 ring magnets.
Try to put magnets on both ends of the device, e.g. 2 on one and and 2 on the other (aiding mode)
There is an tradeoff/optimization to be made here:
In one case you could delete the ferrite entirely and put the magnets directly on both sides of the gap. This would create a high flux density in the gap that would be mostly parallel to the axis.
However, changing the direction of that strong 0° field to 90° would require a lot of ampturns, and a fast coil cannot have many turns. Also, high flux density necessitates narrower pulses (higher frequency spectral content).
Without a ferrite at the gap, the fast low-turn coil needs a lot of volts (and amps) to overcome the magnet's flux and squeeze/turn it 90° and without the high-turn DC/LF coil, you also lose the ability to adjust the 0° flux density in the gap.
On the other hand, low flux density requires a larger metal ring (and ferrite). Approximately 70500 Gauss / mm. (e.g.: a 50mm outer diameter ring requires at least 1410 Gauss in the gap, because 70500 / 50 = 1410 ).
That is well within the capabilities of ceramic magnets which can deliver Br of 2300 to 4000 Gauss, depending on their grade.
With the ferrite, however, the magnets move further apart and the flux density in the gap gets weaker ...but it becomes easier for the low-turn coil to squeeze/turn it 90°.
The longer the ferrite, the weaker the flux in the gap and this might require significant DC in the high-turn coil to aid it. That's wasted power.
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Topic: Grenade coil type systems (Read 22151 times)
