variable magnetic reluctance

Discussion in 'Physics' started by Salvador1, Jan 9, 2015.

  1. Salvador1

    Thread Starter New Member

    Jan 9, 2015
    I know that magnetic amplifiers work on the principle of using a dc current induced static saturation field in a magnetic core to vary the amount of inductance of a winding which is called the load winding and uses AC and so varying the inductance of that winding varies the amount of current that passes .

    My question is as follows, is there any material , liquid , gas etc whose reluctance could be changed by any other means than applying a constant dc current field.
    Maybe a material that changes its reluctance from almoust none to some given amount when a current is passed through the material or when an electric field is applied to it ?
    Looking for something like the solid state version of a reluctance motor, when the field is close to the metal poles it has a low reluctance path through the metal , as the poles rotate away the air gap gets wider and the path magnetic resistance gets higher and so the flux varies.

    By the way , is there a material which when goes into saturation looses its magnetism and then starts all over again until again driven into saturation ?

  2. amilton542

    Active Member

    Nov 13, 2010
    Your question doesn't make sense. Are you familiar with the magnetic form of the Ohm law? You could adjust the reluctance of a core by a variable air gap for a given MMF as one example; but this is ferromagnetism, liquids and gases would inherit different magnetic properties depending on the group that they are associated with in the periodic table.

    Consider copper for example, that's a diamagnetic material. Don't be under an illusion that there is only one kind of magnetism out there.
  3. Salvador1

    Thread Starter New Member

    Jan 9, 2015
    hi amilton , well why doesnt my question make sense , imagine a rectangular magnetic core and a DC winding on that core , the dc winding is powered from a dc source , now put another winding on the same core , there would be no current in thatw inding since the primary winding has dc on it. but now if you cut the core in half at one place and insert a rotor much like the rotors coming in reluctance motors you get something that looks like the shaded pole motor.

    as you would rotate the rotor the flux in the core from the otherwise static dc produced field would now change , vary.So now i would gte some current in my secondary coil even with DC on its primary because the flux is now changed with the help of this reluctance rotor, right?

    I was thinking of such a device only being solid state , with no moving parts etc. So I asked are there any materials whatsoever either solid, liquid gas, I dunno, which could exhibit similar properties for a magnetic core as the rotor with varying poles ?

    Like I have a transformer core and at one place of the core there is a " special" kind of metal put in which normally conducts the flux as the whole core but when for example applied current or e field or whatever would now reduce or increase it's magnetic reluctance and so change the flux thrugh the core. That's what I was thinking.
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
    Of course it makes sense in terms of "is there any method...?"

    Other methods might be mechanical, by changing the density of the material, forinstance by coating many small balloons with the magnetic powder and changing the inflation of the balloons.
  5. BR-549

    Well-Known Member

    Sep 22, 2013
    It should be possible. Replace air gap with a dielectric. Apply DC voltage across gap.

    Depending on the dielectric and gap size, it might take some high voltage.

    But it is more easily done with low voltage DC turn.

    Add a diode and the transformer acquires gain and becomes a magnetic amp.

    The V1 and V2 rockets used magnetic amps to stay on course.

    For some good history and doomsday preparation I recommend this for your library.

    Wow......I guess not. Says file to big! That was a small pdf? amplifiers.pdf

    Anyhow......I suggest you put it in your library.
  6. amilton542

    Active Member

    Nov 13, 2010
    Your questions don't make sense because your technical writing is confusing. For example, how on earth does one achieve a shaded pole motor from d.c. alone?

    From what I've gathered you're trying to create a "rotating transformer", when all you've done is rotate an armature in a stationary magnetic field thus it's a generator.
  7. MrAl

    Distinguished Member

    Jun 17, 2014


    Well a normal magnetic core will exhibit this property by passing a DC current through the winding along with the AC current. This is how a swinging choke works for example. The permeability varies with DC current so the inductance drops with increased current.

    To get this to happen any other way would probably require some mechanical means where something has to actually move to create a change in the apparent reluctance. Im not sure if you could use a magnetic fluid here, but that would require pumping fluid in and out of a chamber anyway so that's not solid state either.

    A question to ask yourself is what you want to use this for. There may be another way to get to the end goal which doesnt require this kind of action.
  8. Salvador1

    Thread Starter New Member

    Jan 9, 2015
    amilton the shaded pole motor was just an example and I said taht when one would attach a dc winding on the shaded pole motor and anotjher secondary winding firstly nothing would be induced in that secondary winding but if the rotor was made like those in reluctance motors and if the rotor would be then spinned it would vary the total flux in the core so in such a situation the DC in the primary could now induce a current in the secondary , but this method is no favourable because it needs some mecanical parts to rotate as to change the flux lines through a core or armature.

    I was in seearch for a material which could alter the flux lines through itself by some solid state means , if there even is any.
    the purpose is simple , because an oridnary transformer doesnt work on DC so the only way to change DC to higher lower voltages etc is to either use a rotary converter or some fancy electronics as in switch mode power supplies.