About EMF:
I think a conductive metal ring can short out magnetic flux that passes through it. Copper strip is wrapped around many transformers to short out leakage flux that can cause eddy currents inside the metal which waste energy heating it up.
So say for instance those metal rings worn around people's heads in fairytales. Going by transformer math, coils with fewer turns will output greater current, so a single ring may need to be very conductive, or it won't totally short the flux. However if you make say 5 turns, the resistance requirement is relaxed by 5 times for the same amount of flux shorting. However if you use 5 times smaller wire to do this, the wire's self-resistance cancels out the gain you make. Perhaps RF reception coils already exist tuned with just the right properties.
Another thing could be skin effect. At high frequencies, current flows at the outer edge of the conductor as through forced to the edges by centripetal force. For this reason in radio transmitters, high-power inductors are often made with copper tubing because none of the current runs through the center anyways. Because the current is confined to the edges, it experiences greater resistance. Silver plating is used on some types of wire to give better conductivity at RF. Silver plated wrapping wire is one example. Another thing that has been done is to use stranded, individually insulated copper wires instead of a single large one; the broken up conductor suffers less from skin effect. A flat wire, band, tape, or whatnot also experiences less skin effect; the wider and thinner the better.
At higher frequencies, the ring may become less effective because of wavelength effects. On metal electronic shields, vent holes will allow through wavelengths smaller than their diameters. 1GHz has a wavelength of about 1 foot according to an online calculator. This suggests to me an ordinary conductive band around the head may be effective to a little over 1GHz. The circumference of a 1 foot ring is about 3.14 feet, which should be about 300MHz, so it may resonate at this frequency and it's overtones, 600/900/1200 etc. Specially chosen ferrite beads may be placed on the ring that could damp resonance at the problem frequencies; but possibly reduce the intended effect at other frequencies.
If a ring were designed to have the same harmonic attributes as an available crystal, perhaps the crystal could be used with the ring in such a way as to eliminate these effects (however crystals can be overdriven - the number of turns in the ring could perhaps be chosen to best suit the crystal). I do wonder if ancient societies have used all these ideas in the past.
Perhaps nice looking necklaces/chokers/headresses could be made fitting this requirements, using gold or silver plated copper wire. OHFC copper is more conductive and may or may not be worth using. Multicolor enameled copper wire could be twisted or braided and this would allow some creative freedom as well as reduction of skin effect. A flat braid would probably work well, and would also help with uninsulated wire, if there is some problem with the insulation chemicals (many insulations are available, teflon, kynar, "enamel"). One wire from the braid could be broken and fed to a sensor that can give a direct reading on how much EMF is going through your skull at the moment!
Curious thought - what happens if you wear a copper headband in an MRI!?
