RF attenuating material suitable for room-sized deployment - Page 1
Forum section: electronics / rf-microwave

author: benryanau
author_rank: Contributor
timestamp: March 01, 2020, 03:46:27 am
content: I've seen and read about "anechoic"(sp?) foams for audio purposes and get the basics I think, but RF seems a different challenge.ECO stealth technologies seem to rely on angles of reflection more than attenuation on incident RF but I'm not that conversant.All I could come up with was a perhaps a combination of louvres as a trap, or (perhaps in combination with) open cell polyurethane foam impregnated with some mixture of graphite, zinc oxide, a humectant and perhaps a metal salt.Cant think of an inductive side other than dispersed ferrite in some antenna-like matrix for longer wave RF.Phase cancellation is fantasy for my level so it's simple simon stuff for me.DIY cost effective - I think that was inferred somewhereIdeas, wisdom?

author: xmo
author_rank: Regular Contributor
timestamp: March 01, 2020, 04:45:31 am
content: I think an effective do-it-yourself version would be a real challenge. Years ago, I knew several people in the radio paging business. They needed a shielded room to work on the pagers because the system transmitters were on the air all the time. There are companies like Lindgren that sell various sizes of screen rooms. I did see one shop that had created a do-it-yourself version out of copper screen but it was obvious that a lot of work had been involved and it was only partially successful.Keeping RF from bouncing around inside is another matter entirely.I have been inside the real deal. A chamber big enough to drive into with a turntable big enough to rotate a vehicle.I can't imagine what such a thing cost let alone the cost of the instrumentation.

author: geggi1
author_rank: Frequent Contributor
timestamp: June 11, 2020, 04:11:45 pm
content: Depending on the size of your chamber a room buildt as a Faraday cage canbe en option.The wall, floor and cealing must be covered by a conductive material (copper or brass fine mesh or sheet) To reduce the reflection you can try to get the Unobtainium paint used on SEALTH planes like the B2 bomberor try som Chinese web shop for a roll of ESD foam used for packing static sensitive electronic devices.The feed through for services (power and RF) is also an consern. If it is just a small chamber you can probably get away with some RF bulkhead connectors. If it is something larger that also require power compainies like Roxtech do have EMC penetrations.Door and windows will also be an issue.By the way i just remembered that on "Myth busters" they made a faraday cage for some avionics myths about the use of mobile phone.

author: DaJMasta
author_rank: Super Contributor
timestamp: June 11, 2020, 08:45:29 pm
content: There are some discussions on this if you search around a bit on the forum, I know people have experimented with mixing conductive powder into paint/using commercial shielding paints, but have also gone the mesh route. It seems one of the biggest problem with any kind of RF enclosure is sealing - it needs to be damn near airtight to get broadband isolation from outside signals, that means that a tight fitting door with RF fingers around all of the perimeter are basically a must, which is trickier to get mechanically reliable in something as large as a regular room.I think the standard for RF anechoic chambers is ferrite tiles (also quite expensive and heavy) in a sealed faraday cage, then with conductive foam cones seems to be the right general route. Provided you can get a good seal around doors/windows with your DIY design, you may be able to get passable reflection performance by using commercial RF absorber material (tiles or flexible sheets), or even try your hand at making some pyramids from antistatic foam or even testing foil wrapped cardboard cones or something similar (probably not great, but probably affordable enough to be tested if you were so inclined). I've heard of scrap ferrite tiles being available, but I think only when an EMC house goes out of business or upgrades, so I doubt they're easy to find in quantity. Every so often a port-o-potty or trailer sized EMC chamber comes up on auction, maybe that would actually be a better option on the affordable size as the problems will be largely worked out even if it costs a couple thousand bucks.Feed throughs for power and signal are a must and also have to be heavily filtered - if you have a DC power line from a supply outside the chamber, for example, signals can still be picked up on the leads between the supply and the chamber, then reradiated in the chamber on the other side of the feed through unless they're filtered out appropriately!