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bitrex

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- Thread starter bitrex
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bitrex

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- #2

vk6kro

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If there is an easy path then it is easy to produce a large magnetic flux.

This means there will be efficient coupling of energy from the coil causing the flux to a coil that has flux passing through it.

The magnetic field of a permanent magnet can be concentrated in one area by providing a good magnetic path to this area of an air gap. You couldn't really say the magnetic field is "stored" there though. Ignoring trivial paramagnetic and diamagnetic effects, air cannot store a magnetic field.

You probably know that large filter chokes have an air gap so that the choke can carry DC current without the core saturating. This is just a way of making the magnetic path slightly less effective than it was. Again, no power is stored in the air gap.

- #3

uart

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Yes what they are saying is basically true, though it makes certain assumptions. In particular by "near ideal" magnetic material they just mean it has very high magnetic permeability, however they still assume that it has a limited maximum flux density (due to saturation). So it's ideal (or near ideal) in one sense but still very non-ideal in another, and this point is

The problem is that stored energy per unit volume is equal to the product of MMF (H in Ampere-Turns/meter) times Flux-Density (B in Teslas). The more "ideal" a soft magnetic material then the

If you ever do any inductor design this point quickly becomes apparent. You try to design an inductor, you use a nice high permeability core with no air gap, and you find you need relatively few turns to achieve the desired inductance. Ok, at first sight you think that this is a

Consider a semi numerical example. L is proportional to the magnetic permeability times N^2 (for a given core). So if you reduce the permeability to say 1/4 of it's initial value then you need to double the number of turns. But since the permeability is 1/4x and the turns are only 2x then it's clear that you can now have twice the current before you reach the saturation flux density. At saturation the product of B times H is now actually 4 times as large. Similarly if you include an air gap which reduces the overall permeability of the iron circuit to 1/100 of it's original value then you need 10 times the number of turns (for a given inductance) but you can have 10 times the current and therefore 100 times the stored energy before saturation is reached!

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bitrex

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