Questions about cancelation of induced EMF and minimizing eddy currents

In summary, the closed-fork shape is a simpler way to divide up a planar surface area of a wide conductor into small sections. As long as there is EMF induced in at least two neighboring loops, it should cancel out.
  • #1
artis
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I recalled a drawing that was provided in an EM text. Without going in length, the basics is simple - in order to minimize eddy currents one divides up a planar surface area of a wide conductor into small separate sections. As is done in transformer core laminations for example.
In the image a fork like conductor is shown, but I copied and duplicated the original image on the left and added a black connection at the bottom, how would that change the situation?
Now the fork is made up of multiple identical rectangular loops, but all loops share one common conductor that means, I think, that as long as there is EMF induced in at least two neighboring loops it should cancel out due to the opposite current directions that have to go through the same shared conductor?

The only time EMF would not be canceled is when the changing B field exists only within one of the smaller loops as far as I think, and it would only be partially cancelled if the EMF in adjacent loops would be different in magnitude.
eddy.jpeg

Now a second example I wish to ask is this, imagine in this case the loop is stationary and so is the field , it's still a AC field. Now on the left side there is a single rectangular loop, the field passes through it and current is induced in the loop, so far so good.
On the right side there is a rectangle that consists of multiple identical rectangular loops, all again sharing a common side wire.
Is there current induced in the right sided rectangular loop containing multiple loops?
And if so then is it induced in the smaller loops or just the overall outermost loop?
Assume a symmetrical and even flux through the loop area to simplify the question.
My own guess would be that current induction should cancel not just in the smaller loops but also in the outermost loop, because the outermost loop cannot have current through it independently of the smaller loops, given the smaller loops work to cancel the applied flux?

loop induction.png
 
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  • #2
artis said:
My own guess would be that current induction should cancel not just in the smaller loops but also in the outermost loop, because the outermost loop cannot have current through it independently of the smaller loops, given the smaller loops work to cancel the applied flux?
Not sure I understand. Unlike the "open" fork, in the limit the "closed" fork is essentially just a conductor. So there would be no large scale eddy currents in a conductor?
 
  • #3
hutchphd said:
Not sure I understand. Unlike the "open" fork, in the limit the "closed" fork is essentially just a conductor. So there would be no large scale eddy currents in a conductor?
Its not about whether the conductive piece of metal is part of a larger circuit not shown, it is only about how much , if any, current can be induced , and how much, if any, can be canceled from an applied external flux cutting a piece of conductive material in a shape like that shown.
I don't think (maybe I'm wrong) that say if you had a thin but wide planar like conductor that passed current along it being a piece of wire within a circuit that this would make any difference in the magnitude of eddy currents induced within the flat conductor if an external AC magnetic field was cutting it perpendicularly.

A metal like copper has lots of free electrons that can drift within it so I would think such a conductor could support both directional current flow as part of a larger circuit as well as circular current flow that would arise from an applied perpendicular to surface field.
But it does raise in interesting question, would such a scenario shift the directional current to one side - that in which it coincides in the same direction as the eddy loop current...

Either way this is a side thought , the main thought I hope you now understand is just about externally applied field and induced current cancellation.
 
  • #4
Maybe some other members would have something to add?
 
  • #5
I'm not sure I fully understand your question, because it seems too simple. But...
Every conductor loop will have current induced from the B field. You can add (with vectors) the currents in conductors that are shared between loops. With perfect symmetry, the inner conductor currents cancel, but not in the outer loop. Of course there are a whole bunch of assumptions going on here (superconductors, uniform fields, etc.).
 

1. What is induced EMF and why does it need to be canceled?

Induced EMF (electromotive force) is the voltage that is generated when a conductor is moved through a magnetic field. It is important to cancel induced EMF in certain situations, such as in power transmission, to prevent damage to equipment and ensure efficient energy transfer.

2. How can induced EMF be canceled?

Induced EMF can be canceled by using a technique called electromagnetic shielding, where a conductive material is placed around the conductor to block the magnetic field. Another method is to use anti-inductance materials, such as laminated iron cores, which can reduce the magnetic flux and thus minimize the induced EMF.

3. What are eddy currents and why do they need to be minimized?

Eddy currents are circular currents induced in a conductor when it is exposed to a changing magnetic field. They can cause energy loss and heating in conductive materials, which can be problematic in certain applications. Therefore, they need to be minimized to improve efficiency and prevent damage.

4. How can eddy currents be minimized?

Eddy currents can be minimized by using laminated or layered conductive materials, which can reduce the circular flow of current. Another approach is to use magnetic materials with high resistivity, which can decrease the eddy current flow.

5. What are some applications where minimizing eddy currents and canceling induced EMF is important?

Some common applications where minimizing eddy currents and canceling induced EMF is important include power transmission systems, transformers, and electric motors. It is also crucial in high-speed trains, where eddy currents can cause significant drag and energy loss.

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