ELF Shielding experiment

[ElectroMichel]

I am doing a shielding experiment, where I wish to shield against frequencies of 0.5 - 100 Hz. For this purpose, I have chosen Mumetal. Unfortunately Mumetals initial permeability has a dependency on frequency, meaning after around 500-600 Hz the initial permeability will plummet towards 1.
My question is this: what if the mumetal is irradiated simultaneously with a high frequency (above 600 Hz) signal, and an ELF (0.5-100 Hz) signal, will the ELF signal be able to penetrate the mumetal (Assuming that it cannot on its own), or will the combination of the two create a new unique signal that does not classify as being between 0.5-100 Hz?

 

[VEBill]

At the risk of oversimplification: The nice thing about frequencies is that, essentially, (in the absence of nonlinearities) they don't mix.

 

[ElectroMichel]

So basically the ELF signal will travel through the metal the same with or without the presence of a second higher frequency signal (Even if they both irradiate the same area)?

What do you mean by "in the absence of nonlinearities"?

 

[IRstuff]

I don't understand why you need to use Mumetal; what's wrong with plain old copper? How much attenuation do you actually need? A copper mesh works quite well as a Faraday cage. Mumetal is primarily used against magnetic fields; is that what you're shield against?

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[VEBill]

If a medium or circuit is linear, then each spectral component remains on or within its original bandwidth. Each signal has no effect on the other. That's why there can be millions of radio signals 'on the air' at once, or 500+ TV channels on a cable.

As soon as a medium or circuit is nonlinear, then signals begin to mix, generating sums and differences; as well as generating harmonics. In such cases, signals can start to interact.

This fundamental concept is quite useful, even when applied to the sort of question being asked here.

 

[VEBill]

I've read of physics experiments where an active circuit ("servo") was used to counteract and cancel out magnetic fields.

 

[ElectroMichel]

How do you know if the medium is nonlinear or linear?

 

[VEBill]

Analysis, or experience. It's simply the straight line (or not) response.

Amplitude also plays a role. It is possible for magnetics to become nonlinear (e.g. saturation of a transformer core).

The description of your experiment didn't seem to be a case where the amplitudes involved would be sufficient to endanger an assumption of linearity. So the concept seemed useful to help quickly answer your original question.

If one frequency did affect the other, then it might be a useful technology with unexpected applications.

 

[ElectroMichel]

What happens on an atomic level when dealing with linearities and non-linearities?

 

[VEBill]

Magnetics happens at the domain level.

Here's a quick wiki link to an initial explanation:

https://en.wikipedia.org/wiki/Saturation_(magnetic)#Explanation

 

[ElectroMichel]

how does the magnetic saturation of an alloy, explain why signals mix or not?

 

[Comcokid]

I once had to correct a product problem on a consumer telephone answering device where the internal power transformer was coupling into the internal transformer of a standard 'Ma Bell' telephone. Other engineers were trying multiple layers of mu-metal as shielding but this solution was very expen$ive. I used standard silicon steel sheet - same material used to punch E I laminations for power transformers from. This gave much greater attenuation (shielding) than the mu-metal for only a few cents rater than several dollars.

 

[VEBill]

This has drifted very far away from your original question.

 

[hacksaw]

Since an experiment is being planned or performed, just try it and post your findings!