/diy/ - Do It Yourself

>>1512734
Oh beans, I meant to say APRS.

>>1512783
Physicist here, all substances have atomic and molecular resonances that absorb radiation. Generally speaking, these are in specific groups, some of which absorb microwaves, some of which absorb visible light or IR, some of which absorb UV and X-rays, etc. Microwaves in particular are absorbed readily, and it's the electric (not the magnetic) part of the light wave that is absorbed by the charges of the atom/molecule. Basically the electrons and nuclei are bound to one another by an attractive force, and the presence of an electric field pulls the two apart much like a spring. Like any system with a spring, these have a resonance frequency at which they best absorb the driving energy, and since all atoms and molecules have fairly similar structures and hence energy levels, these absorption frequencies are in similar bands. You can see this expressed in the electric permittivities of the substances, a purely real value means the sine's argument remains purely imaginary (exp(iaωt)), but a complex permittivity leads to both a real and imaginary part of the argument (exp(iaωt)*exp(bωt)), the real part will give a decaying exponential, which is how the absorption of light in a medium is expressed in terms of EM waves. So if you take a look at a chart of air's complex permittivity (or refractive index) as a function of frequency, you'll find increases in the imaginary part corresponding to absorption bands. You may have to do a little math to figure out the absorption rate from these values, however.

>>1175169
Pic actually related.