[Amps] FW: RFI Question

[KD7QAE]

Interesting.  There is an optical technique called the "crab's eye lens" 
which uses a deep parabola with a detector (non imaging) at the top of 
the curve.  It works by  glancing reflections of the light entering the 
open end making it to the detector without being able to make the 
roundtrip back out before first hitting the detector.  If the walls were 
lossy and the curve approximated by straight lines, one would have the 
inverse of the usual pyramids used in anechoic chambers.  I wonder if 
they would work as well?

Tomm

m.ford wrote:

>----- Original Message ----- 
>From: "Peter Chadwick" <g3rzp at g3rzp.wanadoo.co.uk>
>To: "Larry Carman" <lncarman at swbell.net>; "'Brass Pounder'" <wf3j at comcast.net>
>Cc: <amps at contesting.com>
>Sent: Saturday, February 04, 2006 12:39 PM
>Subject: Re: [Amps] FW: Â RFI Question
>
>
>  
>
>>Larry asked:
>>    
>>
>>>Exactly what is the composition of radar
>>>      
>>>
>>absorbent material and how is it applied to the metal surfaces? How does rf
>>absorbent material react to different ranges of wavelengths?<
>>RAM (Radar Absorbent Material) varies, depending on the application. For anechoic chambers, it's usually in the form 
>>of pyramids of some foamed plastic, heavily loaded with graphite, and is pretty filthy stuff  to be touching as you're 
>>setting up in the chamber. This works reasonably well dow to around 400MHz, depending on the size of the  pyramids. 
>>For lower frequencies, powdered ferrite is added to the mix, and even ferrite slabs are used, placed under the 
>>pyramids. It has been known for enough energy to be absorbed from a microwave transmitter/antenna in an anechoic 
>>chamber for the pyramids to be heated to the point where they catch fire! Very nasty, with lots of toxic gases and 
>>fumes, and carbon dirt EVERYWHERE!
>>Stealth aircraft rely heavily on the reflection back to a monostatic radar being low, because the signal goes off in 
>>another direction - this caused by the geometry of the various surfaces: I suspect the RAM used there is a resistive 
>>material, possibly with ferrite loading again.
>>73
>>Peter G3RZP
>>_______________________________________________
>>    
>>
>
>
>As I understand it, the surface of the pyramids reflect the wave
>deeper and deeper into the panel where they cannot escape by
>reflection and are thus attennuated.
>
>Mike k1ern
>
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