cheapest microwave EM absorber? - Page 1
Forum section: electronics / rf-microwave

author: CopperCone
author_rank: Super Contributor
timestamp: September 07, 2017, 09:21:44 pm
content: I would like to make a wall which absorbs EM energy. I have been in the compliance laboratory a few times, and they used cardboard that is lined with ferrite inside of the anechoic chamber (which itself was metal). I would just like a single surface to be layered with the stuff, to prevent reflection in 1 plane. IIRC they said the cardboard ones are pretty cheap.I see most of the options are quote only. Does someone experienced in setting these things up know where the best deals are?I am only interested in absorbing microwave >1GHz at this time.I have seen the setup before at a university, they had a single wall lined with cones that absorb energy and they had a rotational platter and a horn in front of it, to test the antenna. I would say it was less then 5x5 foot.

author: Marek85
author_rank: Contributor
timestamp: September 11, 2017, 02:16:21 pm
content: I heard of EMC PIONEERwww.emc-emi.comits a Chinese supplier for anechoic chambers, filters and accessories. I don't know how the prices compare to US market but I think they are cheaper than EU suppliers like Frankonia or ETS-Lindgren.

author: coppice
author_rank: Super Contributor
timestamp: September 11, 2017, 02:42:00 pm
content: Quote from: Marek85 on September 11, 2017, 02:16:21 pmI've used 2 chambers built by Pioneer. They probably aren't as expensive as a western brand, but they still ain't cheap.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 11, 2017, 03:50:24 pm
content: There is a free, but nasty source of microwave absorbers. Products designed to crisp in the microwave have a printed layer of stuff to absorb somewhere in/on the packaging. Each piece is only about 10 cm by 10 cm so there will be a lot of dumpster diving to salvage enough for any decent chamber. Of course if you know the location of a large software shop you could probably get enough microwave popcorn wrappers in a week or so.I have never characterized it so don't know if it is "tuned" or broadband, though I would assume the particle sizes are nominally graded to optimize just above 1 GHz. But I am sure that cost drivers mean they don't screen the particle sizes and spacings very carefully so it should work over a fairly broad band.

author: SeanB
author_rank: Super Contributor
timestamp: September 11, 2017, 07:19:30 pm
content: Normal black oxide powder, used as a paint and concrete colourant, is often available at hardware stores or art suppliers, and is pretty lossy at microwave frequencies. Blend it with acrylic paint and it will be a reasonable absorber. It is just iron oxide powder.

author: MikeLogix
author_rank: Contributor
timestamp: September 11, 2017, 09:18:59 pm
content: Have a look at this stuff. Not sure of price however.http://www.eccosorb.com/products-eccosorb-high-loss-absorbers.htm

author: edpalmer42
author_rank: Super Contributor
timestamp: September 12, 2017, 01:49:42 am
content: Quote from: CatalinaWOW on September 11, 2017, 03:50:24 pmMicrowave browning paper is available on a roll.http://www.ebay.com/itm/332271823236Another possibility is antistatic foam. The older style is black and is somewhat conductive. I think it should absorb RF, but I have no idea how well it would work. Looks like it's available on ebay.Ed

author: CopperCone
author_rank: Super Contributor
timestamp: September 12, 2017, 01:55:06 am
content: i think microwave cooking uses titanium oxide, I am not sure of the frequency performance of it. interesting thought. I think they typically use some kind of ferrite.. i'm guessing mesh size is important.

author: SeanB
author_rank: Super Contributor
timestamp: September 13, 2017, 08:14:12 pm
content: Black antistatic foam works well, though you need to have the patterned version to act as an absorber and notr a poor reflector. Too high a power and it tends to turn into charcoal, though it is still usable in that state. Used in a Radar test station as dummy load, with 2kW of pulses dumped into it. New foam would smoke for the first hour or so before settling down and becoming brittle. The other dummy load was a tapered waveguide section filled with a slurry of epoxy and iron filings, which also got really hot.just wonder how a few bags of regular charcoal ( or even the compressed powder briquettes) would work as an absorber, being pure carbon on the charcoal side, and powdered carbon and clay on the briquette ones. Not going to test this in my microwave though, I kind of like to use it every so often.

author: dcarr
author_rank: Regular Contributor
timestamp: September 13, 2017, 09:24:44 pm
content: Sean,Can you give an example of the "patterned foam" you mentioned? I'm not familiar with that type.David

author: edpalmer42
author_rank: Super Contributor
timestamp: September 13, 2017, 09:56:14 pm
content: Obviously, for this application, the absorber won't be getting hot due to the RF. But that does raise the point that depending on where this 'wall' is installed, flammability might be an issue. A wall stuffed with charcoal could be a really bad idea. Maybe the OP should keep that in mind.Ed

author: CopperCone
author_rank: Super Contributor
timestamp: September 14, 2017, 03:08:34 am
content: it would be something temporary to put up.i think using the sky as a backdrop is actually a better idea, and making some kind of elevation platform. just need to normalize

author: SeanB
author_rank: Super Contributor
timestamp: September 15, 2017, 08:30:01 pm
content: Quote from: dcarr on September 13, 2017, 09:24:44 pmHere we go, this in a black conductive foam rather than plain or pink dissipative foamhttps://www.uline.com/BL_863/Convoluted-Foam-Setsedit, found the conductive stuff as well.https://www.uline.com/Product/Detail/S-14641/Foam/Convoluted-Foam-Sheets-48-x-96-x-2

author: Ian.M
author_rank: Super Contributor
timestamp: September 15, 2017, 08:44:09 pm
content: I wonder how well stacked 2L PET bottles full of salt water would do? You'd need two layers deep, offset because of the gaps between them.

author: dcarr
author_rank: Regular Contributor
timestamp: September 15, 2017, 08:54:08 pm
content: Thanks, Sean.I've seen that foam before, but didn't know the name. Makes sense that it would break up the reflection.David

author: cdev
author_rank: Super Contributor
timestamp: September 18, 2017, 04:36:39 am
content: I made some ghetto foam a few years ago. It used a lot of activated charcoal. I just ladled it in. You should make it in layers with the most carbon close to the back which should be metal, then transition to air with layers of less and less charcoal-dense foam.

author: CopperCone
author_rank: Super Contributor
timestamp: September 18, 2017, 11:05:26 am
content: how did your hood construct work out?