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Author Topic: cheapest microwave EM absorber?  (Read 1181 times)

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Offline CopperCone

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cheapest microwave EM absorber?
« on: September 08, 2017, 07:21:44 AM »
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.
« Last Edit: September 08, 2017, 07:23:56 AM by CopperCone »
 

Offline Marek85

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Re: cheapest microwave EM absorber?
« Reply #1 on: September 12, 2017, 12:16:21 AM »
I heard of EMC PIONEER www.emc-emi.com its 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.
 

Offline coppice

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Re: cheapest microwave EM absorber?
« Reply #2 on: September 12, 2017, 12:42:00 AM »
I heard of EMC PIONEER www.emc-emi.com its 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.
I've used 2 chambers built by Pioneer. They probably aren't as expensive as a western brand, but they still ain't cheap.
 

Offline CatalinaWOW

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Re: cheapest microwave EM absorber?
« Reply #3 on: September 12, 2017, 01:50:24 AM »
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.
 

Offline SeanB

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Re: cheapest microwave EM absorber?
« Reply #4 on: September 12, 2017, 05:19:30 AM »
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.
 

Offline MikeLogix

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Re: cheapest microwave EM absorber?
« Reply #5 on: September 12, 2017, 07:18:59 AM »
Have a look at this stuff. Not sure of price however.
http://www.eccosorb.com/products-eccosorb-high-loss-absorbers.htm
 

Online edpalmer42

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Re: cheapest microwave EM absorber?
« Reply #6 on: September 12, 2017, 11:49:42 AM »
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.

Microwave browning paper is available on a roll.  http://www.ebay.com/itm/332271823236

Another 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
 

Offline CopperCone

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Re: cheapest microwave EM absorber?
« Reply #7 on: September 12, 2017, 11:55:06 AM »
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.
 

Offline SeanB

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Re: cheapest microwave EM absorber?
« Reply #8 on: September 14, 2017, 06:14:12 AM »
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.
 

Offline dcarr

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Re: cheapest microwave EM absorber?
« Reply #9 on: September 14, 2017, 07:24:44 AM »
Sean,

Can you give an example of the "patterned foam" you mentioned?  I'm not familiar with that type.

David
 

Online edpalmer42

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Re: cheapest microwave EM absorber?
« Reply #10 on: September 14, 2017, 07:56:14 AM »
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
 

Offline CopperCone

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Re: cheapest microwave EM absorber?
« Reply #11 on: September 14, 2017, 01:08:34 PM »
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
 

Offline SeanB

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Re: cheapest microwave EM absorber?
« Reply #12 on: September 16, 2017, 06:30:01 AM »
Sean,

Can you give an example of the "patterned foam" you mentioned?  I'm not familiar with that type.

David

Here we go, this in a black conductive foam rather than plain or pink dissipative foam

https://www.uline.com/BL_863/Convoluted-Foam-Sets

edit, found the conductive stuff as well.

https://www.uline.com/Product/Detail/S-14641/Foam/Convoluted-Foam-Sheets-48-x-96-x-2

« Last Edit: September 16, 2017, 06:31:34 AM by SeanB »
 

Online Ian.M

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Re: cheapest microwave EM absorber?
« Reply #13 on: September 16, 2017, 06:44:09 AM »
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.
 

Offline dcarr

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Re: cheapest microwave EM absorber?
« Reply #14 on: September 16, 2017, 06:54:08 AM »
Thanks, Sean.

I've seen that foam before, but didn't know the name.  Makes sense that it would break up the reflection.

David
 
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Offline cdev

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Re: cheapest microwave EM absorber?
« Reply #15 on: September 18, 2017, 02:36:39 PM »
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.
"What the large print giveth, the small print taketh away."
 

Offline CopperCone

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Re: cheapest microwave EM absorber?
« Reply #16 on: September 18, 2017, 09:05:26 PM »
how did your hood construct work out?
 


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