EMF shielding using a conductor

In summary: This makes a lot of sense.In summary, Eddy currents are induced in a conductor when a changing magnetic field opposes the change in magnetic flux, and this causes the fluctuations to be mitigated. This is why metals appear shiny when they are near a coil.
  • #1
KDPhysics
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Homework Statement
How does placing a conductor in the path of a magnetic field of a circular coil shield anything behind the plate?
Relevant Equations
Lenz's Law
So I've been trying to figure out how EMF shielding works. More specifically, I've seen videos where placing a metal conductor in front of a circular coil (with AC running through at radio frequencies) apparently shielded anything behind it.

After searching online, I repeatedly saw Eddy currents popping up.

If I've understood everything correctly, when you place a conductor near a changing magnetic field (such as that of a circular coil), nature abhors any change in magnetic flux. Consequently, a current will be induced, called Eddy current, in the conductor, such that the induced magnetic field opposes the change in magnetic flux.

For example, I have the following set up (a circular coil attached to an AC supply and a conductor beneath it):
IMG_20200524_223939.jpg

Now consider an arbitrary instant in which the coil's magnetic field is decreasing. Then, by Lenz's law an Eddy Current will be induced in the conductor trying to "undo" this decrease in magnetic flux. Consequently, the current will be such that the induced magnetic field points in the same direction as the external magnetic field.
But then there still is residual magnetic field behind the conductor due to both the decreasing external field and the induced field. So, shielding has not occurred?
 
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  • #2
The fluctuations will be mitigated by the induced currents and Lenz's Law. A good Faraday Cage can greatly reduce Radio frequency interference.
This is also why metals appear shiny.
Not static fields!
 
  • #3
Oh, I see. So exactly because the external magnetic field is decreasing, the fact that we have an induced magnetic field keeps the change in magnetic flux approximately constant, thus shielding anything behind.

EDIT: Also, could you elaborate on why this causes metals to be shiny? Sounds very interesting.
 
  • #4
Yes. And of course a conductor will also shield both static and dynamic E fields.
 
  • #5
One question: if initially (before turning on the AC supply) there is no magnetic field outside, and then after some instants, as we saw in my diagram, there is a net magnetic field outside, this means that there must be some net change in flux right? Perhaps the moment the AC supply is turned on there is a surge in induced current, and then this stabilizes?
 
  • #6
Exactly.
And the light is reflected from a conducting surface because field components are forced to be zero at the surface...this produces a reflected wave like sound off a hard wall...its a little more complicated for light but that is the fundamental issue.
 
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  • #7
Oh ok thanks.
 

Related to EMF shielding using a conductor

1. What is EMF shielding using a conductor?

EMF shielding using a conductor is a method of reducing or blocking the effects of electromagnetic fields (EMF) by using a conductive material to create a barrier. This barrier absorbs or reflects the EMF, preventing it from reaching the surrounding area.

2. How does EMF shielding using a conductor work?

EMF shielding using a conductor works by creating a conductive barrier between the source of the EMF and the surrounding area. This barrier absorbs or reflects the EMF, preventing it from passing through and reducing its strength. This is known as the Faraday cage effect.

3. What materials can be used for EMF shielding using a conductor?

There are various materials that can be used for EMF shielding using a conductor, such as copper, aluminum, and steel. These materials are highly conductive and can effectively block or absorb EMF.

4. Is EMF shielding using a conductor effective?

Yes, EMF shielding using a conductor can be effective in reducing or blocking the effects of EMF. However, the effectiveness may vary depending on the strength and frequency of the EMF, as well as the quality and placement of the shielding material.

5. Are there any potential risks or drawbacks to using EMF shielding using a conductor?

While EMF shielding using a conductor can be effective, there are some potential risks and drawbacks to consider. For example, if the shielding material is not properly installed or maintained, it may create gaps or holes that can allow EMF to pass through. Additionally, using conductive materials in certain environments, such as near electrical equipment, may pose a fire hazard. It is important to carefully consider and address these risks before implementing EMF shielding using a conductor.

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