----- Original Message -----
From: "Peter Chadwick" <g3rzp@g3rzp.wanadoo.co.uk>
To: "Larry Carman" <lncarman@swbell.net>; "'Brass Pounder'" <wf3j@comcast.net>
Cc: <amps@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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