can inductive coupling change the value of inductance?

[kwagjj]

I'm confused about the influence of inductive coupling.

Say there's an on chip inductor.

Would the L value of this onchip inductor change if some external magnetic flux is applied?

On one thought, the L value seems to be a fixed and fundamental value that cannot be changed once designed.

On the other hand, sine the inductance if eventually a function of magnetic flux, if we can change the magnetic flux perhaps the inductance value could change??

 

[chuckey]

An external magnetic field will effect the permeability of any core used, if it is saturated its relative permeability become one. If you use a short circuit coil and magnetically link it to the field of the coil, the apparent inductance of the coil will fall. Like wise if you introduce a piece of ferrite, the value of the inductor will seem to rise.
An external field out side of the above cases will have no effect UNLESS specially engineered. i.e. a coil carrying a certain frequency is purposefully linked to another source of that frequency which will then modify the current in it so the inductors value seems to have changed.
Frank

 

[BigBoss]

Every Magnetic and Electrical field will result some changings in Inductor value and Q Factor by definition of Inductance.See. Magnetic Flux and Fielad equations.

 

[kwagjj]

An external magnetic field will effect the permeability of any core used, if it is saturated its relative permeability become one. If you use a short circuit coil and magnetically link it to the field of the coil, the apparent inductance of the coil will fall. Like wise if you introduce a piece of ferrite, the value of the inductor will seem to rise.
An external field out side of the above cases will have no effect UNLESS specially engineered. i.e. a coil carrying a certain frequency is purposefully linked to another source of that frequency which will then modify the current in it so the inductors value seems to have changed.
Frank

Thanks for such an insightful answer
I really needed to know the external case where if the frequency is the same as the onchip inductor, then the external magnetic field can change the L value.

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Thanks for the reply
I really should check out the equations relating L with magnetic flux.
But intuitively I expect chuckey's reply to be right though.

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Thanks for the reply
I really should check out the equations relating L with magnetic flux.
But intuitively I expect chuckey's reply to be right though.

 

[volker@muehlhaus]

I really needed to know the external case where if the frequency is the same as the onchip inductor, then the external magnetic field can change the L value.

You might see an effect from mutual inductance. Current in other inductors or traces induces current in your inductor. If this is the same signal path, coupling between different on-chip inductors, or coupling of an on-chip inductor with signal lines, can be a problem and the layout must be designed with care.