Re: [Amps] FW: RFI Question

[Peter Chadwick]

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