For a mag circuit that goes partly though air though, the decrease in permeability is abrupt and very significant. This means to understand your setup you have to figure out what the magnetic circuit is and what the circulation path lengths are.įor a magnetic circuit that is made from all core material and no air, the permeability is just about the permeability of the core because the flux is always through a magnetically active material with high permeability relative to air. The next most important thing is the magnetic circuit itself, in that the flux is said to circulate similar to the way an electrical current circulates in an electrical circuit. To get a rough idea of permeability wind a 100 turn coil, measure its inductance, then put it over the ferrite, measure the inductance again, divide the latter by the former to get rough permeability, this is only ball park.Īs a rule the most important thing about a magnetic circuit is distance which in a magnetic circuit means length. One difficulty with higher power is that the core will tend to saturate when its mate is not in range, as forcing the magnetic field to go through the air when the transformer is split will massively lower its inductance, a self resonant design is probably the way to go.
If you really want to use ferrite maybe you could find a circular ferrite core smps transformer and use it in its 2 halfs with a winding on each, if you can get them a mm or so close togther you stand a chance of decent power transfer. I've had success with wireless power as you've seen in your other post, 50ma or so is easy, an amp wouldnt be so hard. Commercial 'phone chargers use ferrite, I had a look inside one, but the coil is a pancake coil not a stick, a am aerial type loopstick will have a ui or permeability of about 3000, but it wont be a fat lot of use for wireless power as the magnetic field will be concentrated at the smaller diameter not so much across the width, I'm not an expert in the field however the larger the face area the better.
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