Powering electronics inside of a Faraday cage

[IdahoMan]

The requirement: Electronics inside of a Faraday cage need to be strictly shielded from transmitting or receiving any EM radiation (light might be ok in certain situations), but it must be powered.

Simple solution that comes to mind would be:

-Metal (solid or mesh) box (or room) with the right seals.

-As for power, would simply "separating" a transformer to where the primary is on the outside of the box and the secondary on the inside work? Would there be any issues with the magnetic field or "eddy currents".

This subject has good security and test-equipment potential.

Thanks.

[Jeroen3]

RF testing houses just have a passthrough box with lots of ferrites.

[Ian.M]

You cant split a transformer with a full Faraday shield between primary and secondary - the shield is equivalent to a shorted turn and will cause massive losses.   Electrostatically shielded transformers are possible, but in their construction the shield is split, usually with an insulated overlap, so it doesn't form a complete turn round any limb of their core, and as a result it cant provide any magnetic shielding.

One approach to getting power into a fully shielded enclosure is mechanically.  Its possible to maintain a good electrical contact round a rotating shaft, so a motor on the outside and a generator on the inside can deliver as much power as you need with no possibility of EM leakage - as long as good contact is maintained round the shaft.

[james_s]

Depending on what the power requirements are, a quick & dirty method that guarantees isolation is to power the equipment with batteries located inside the cage.

[scatha]

We use Ramsey Electronics RF shielded enclosures at work which include RF filtered AC/Ethernet/USB connections. They provide 80-90 dB isolation between 1-6 GHz, not sure about the performance at higher frequencies.

[David Hess]

Usually feedthrough capacitors mounted to a conductive bulkhead which is part of the Faraday cage are used and this would be my first choice.  These may form part of an LC circuit.  Mechanical and optical power transmission are also feasible.  Some extreme isolation applications use acoustical transmission of power through a piezoelectric transformer.

[ahbushnell]

If you want to build a screen room there are filters made for that purpose.

http://www.ramayes.com/EMI_RFI_Filters.htm

These are power filters. 
http://www.ramayes.com/EMI_RFI_Filters.htm#Power%20Line%20Filters

[Amper]

From y experience in EM labs they always use batteries as much as they can. High power for automotive inverters is fed in with heavy filter boxes, though they are mostly used only as a known characteristic for the measurement, since they will not block all RF.

As Ian.M said mechanical could be the way to go, though it also depends on your power and shielding demand. Grounding the mechanical feed through will only get you partway, it is very difficult to get a seal all around the shaft wile its spinning fast. If you want to go all the way you could use liquid metal sealed around the shaft. Another way could also be to use hydraulics, a pump and a motor, each with a generator/motor, getting the liquid shielded should be pretty easy with small enough pipe diameter and the transmittable power an be gigantic.

For ow power maybe optics? Laser through a mesh or a fiber lighting a solar cell.