Solving the Problem of Unwanted Mains Supply Field in a Faraday Box

[arrektor]

Hello,

I have constructed a Faraday box with alluminium sheets having holes on them.
The problem is that the mains supply field is not canceled within this box.

The box is about 50cmx50cm and hosts a number of electrodes and an electrical drive that moves these system of electrodes.

I suppose that the reason that I still get field inside the box is the wires of this electrical drive.

Is there a way to cancel that as well?

Thank you

 

[f95toli]

No, the reason is most likely inductive pickup. A Faraday cage will protect you from high-frequency electromagnetic radiation; but it is useless against inductive pickup since the aluminium won't attenuate (quasi) static magnetic fields.

In order to cancel out mains frequency inside the box it needs to be made of e.g. mumetal or something similar.

That said, it is of course possible that some of the mains interference is due to pickup elsewhere (the electrodes).

 

[arrektor]

Thank you.

The most probable is the pickup on the electrodes.

The problem is that the Faraday box works better when it is not earthed, then at some point noise starts to appear in the recording channels of the electrodes.

To eliminate the noise, I Earth the Faraday box for a couple of minutes but then the disconnect it.

This lasts for 1-2 hours and needs to be done again.

If I do not disconnect the earthing wire from the earthing, noise appears (most probably coming from the earthing, as it is basically being earthed in the Earth channel of the mains supply) As soon as I disconnect it it is smooth and noiseless for a couple of time.