Radio and Micro Wave Attenuation?

Question

Which materials attenuate (weaken) radio and microwaves the best? And how much of each material is needed to completely attenuate a radio wave? Also, how long/far can radio waves travel in air before before becoming too weak to receave? Thanks.

Answer 1

They use some absorber material in anechoic chambers that can absorbs pretty much everything, they have these big foam spikes. In the one I saw the foam spikes are about 2 feet tall and the microwave source they are firing into it is several GW.

I think the distance they can travel in air depends on the frequency. If the frequency is far away from any resonance frequencies in air the air will be transparent to them and it should cause no loss. Any extra electron density will however cause some absorption, this is a problem when you are sending a signal to a satellite, the plasma will absorb some of the waves.  

Answer 2

the best way to deaden a signal is by building a faraday cage. that will compleatly absorb the wave. microwaves do not have to travel a set distance. the distance they can be recieved from depends on power of transmition. frequency of the wave and the curvature of the earth.  there are microwave tower in the USA and australia that communict with each other through the ocean. so i would say they go pretty far.

http://en.wikipedia.org/wiki/Faraday_cag...

http://en.wikipedia.org/wiki/Ultra_low_f...