BLOCK EMF
 

Wall paint, fabrics, etc...

http://www.blockemf.com/catalog/index.php?cPath=763

Re: BLOCK EMF
 

At those prices the only thing being protected would be my money, from my wallet. $460.00 for a gallon of paint??

Re: BLOCK EMF
 

aluminum foil works at most frequencies.

Re: BLOCK EMF
 

Is this why foil hats are so popluar?

Re: BLOCK EMF
 

Chicken wire and other close spaced
wire fence, can make a farday cage.

That can shield against e.m.p and e.m.f.

Re: BLOCK EMF
 

The active ingredient in RF shielding is usually just powdered iron. And powdered metals (of just about any type) cost a lot of money.

Now I don't know what that place is selling exactly, and that doesn't mean that they're not reaming you anyway, but you can make "RF shielding" paint yourself just by mixing a LOT of powdered iron into any kind of paint you want. The more iron you put in and the thicker you layer it on the better it works.

Other conductive metals will work, but powder iron is the best. Iron or steel filings can work also, if you don't care what the paint surface looks like. Oil-based paint should be used as latex is porous and absorbs moisture, and moisture will eventually rust the iron and ruin it for RF shielding. I have read that oil-based varnish is better to use than any paint, because varnish is clear and so you can see the amount of iron coverage in it.

(--The paint originally used on the earlier stealth airplanes was sensitive to water the same way: B-2's had to be completely repainted if they were flown through the rain or got wet at all. The stealth paint they're using now is said to be much more durable--)

Most powdered metals are also highly explosive; working with large quantities of them is never safe. A spark from static electricity can light them, but you can't run a humidifier because the water will contaminate them badly also. So you have to always true-ground everything, even yourself (that is--wear an ESD strap).

Well, yes and no. The thing is the hole size.

If the wavelength of a RF signal is shorter than the diameter of the holes, then the RF will be able to pass through. The prime example of this is microwave ovens--the wavelength they put out is up around 10cm long, but the holes in the door screen are always far smaller than that, only 3-4mm across.

A piece of hog panel fencing will protect you really well from the 60 Hz AC wall current EMF, but won't do hardly anything against microwaves, for example.

It would be much safer to use pieces of plain sheet steel. Aluminum would work and will not rust in most situations, but the steel would work better for RF shielding because it contains mostly iron.



-end-

Re: BLOCK EMF
 

for low frequency RF (below 100k) it helps to have a material with some iron content like cold rolled steel.

for general electronics packaging ... machined aluminum works good.

at higher frequencies ... gold and/or silver and/or copper plated, machined aluminum. also, stainless steel.

but i don't know what frequencies the brainwave scanner's work at so i would have to say a proper tin foil hat would have a layer of cold rolled, some sheet aluminum, AND gold leaf. just to be sure.

Re: BLOCK EMF
 

Haha Thanks.^

Re: BLOCK EMF
 

Faraday Cages work on Gauss' Law. Gauss' law only applies to an entirely enclosed space.

If you just paint your roof and walls, EM waves will propagate top to bottom just fine. Also, you have to make sure that the entire thing is very conductive to every other part of the entire thing, which iron embedded paint may not be able to do.

Re: BLOCK EMF
 

The place I used to work had covered the walls in the computer lab with a paint that contained powdered copper. I don't recall it being on the ceiling or floors, but definitely on the walls. They were that nice reddish/orange-ish copper color because they didn't do it for looks...

I can't say how well it did vs all kinds of radiation, but I know for sure that radio waves couldn't make it through it. I could have a radio playing (FM) and walk through the lab door and instantly get static. It was kind of cool...

Re: BLOCK EMF
 

i am more familiar with the term Faraday Cage, the practice of completely enveloping a DUT (device under test) in a conductive material (where the material chosen depends on the frequencies to be reflected/ attentuated).

for example ... if we are ever required to carry ID's with transceivers, i will likely have an aluminum pouch (that completely envelopes the ID) to carry mine in.

of course, the 'depth' of apertures matters too. e.g. a honeycomb mesh with holes 1/8" across will attenuate RF more than a simple wire screen mesh with holes 1/8" across.

side note ... the last time i measured attenuation on a honeycomb mesh, the guy who helped me get the tools was a really helpful tech. a year later he got laid off & came in and shot (killed) the VP of manufacturing (that laid him off). and i just knew Larry as a tech who was willing to help a recent new-hire collect the instruments for a little EMI testing. (this happened at Elgar, a UPS manufacturer, in San Diego in 1990/1991). :offtopic:

anyway ... attenuation matters too. e.g. you can add iron powder to epoxy to create a material that converts RF to heat (which is sort of a description of a microwave load that instrument manufacturers sell). or, make a box out of iron-powder-filled epoxy - and it will attenuate most (all ?) RF energy that comes its way - without any truly conductive surfaces.

so ... back to the ULTIMATE tin-foil hat. in addition to the layers of cold-rolled, aluminum, and gold, it should have a layer of attenuating material - water, molded epoxy that has iron as a filler material ... etc.

i wonder if i could sell those ?

in a pinch, this position will work too - :headsand:

Re: BLOCK EMF
 

A tin-foil hat that isn't grounded, is an antenna!