Penetration versus Frequency

Question

I would like to know the relation between penetrating ability and the frequency of a wave. For example, gamma waves have high frequency and high penetrating power: intuitively I imagined this as attacking a target rapidly in quick succession and managing to get through.

But the penetrating ability is also a feature of low frequency waves - the usual telecommunications spectrum. What is the intuition behind this? Are there other factors like the field which play a dominating factor here?

Edit: The question is in reference to the permeable zone indicated in this figure.

Answer 1

That's a complicated question because different frequency waves are absorbed/scattered by different mechanisms and in different media. Have a look at http://en.wikipedia.org/wiki/Mass_attenuation_coefficient as this contains some introductory information. Actually that article describes X-Ray absorption in some detail but glosses over light and radio waves.

You specifically mention radio and low frequency waves and http://en.wikipedia.org/wiki/Radio_propagation gives some discussion of these. Low fequency EM is generally too low energy to be absorbed by exciting molecular transitions and instead it's absorbed by interaction with the electron is whatever it's passing though. generally speaking the more conducting the media the faster the radio/VLF waves are absorbed.

Answer 2

This is more of an addendum to @JohnRennie's answer, outlining your confusion a bit more clearly:

Normally, the gamma-rays-more-PP is for metals etcetera. These have free electrons and the electrons can absorb pretty much anything. Gamma rays, being more energetic, preserve themselves much better that Xrays, radiowaves, etc. Concrete is a composite, so I don't know exactly what goes on inside it, but it's probably something similar.

On the other hand, gas molecules in the air can only absord fixed amounts of energy (above the ionization energy, they can absorb anything)? Since $E=h\nu$, fixed energy $\implies$ fixed frequency. These fixed frequencies are mostly in the UV/Xray/gamma ray range for air. There are enough of these fixed frequencies(due to orbitals, etc) that they basically black out most of the the Xray spectrum. Aside from that, the reaction $3O_2 \overset{h\nu}{\rightleftharpoons} 2O_3$ absorbs UV light in the ozone layer.

On the other hand, radio waves aren't strong enough to be absorbed by an atom, they are probably below the quantum of energy for the atomic system. So they pass through space unhampered, and since they diffract easily, we get the extra benefit of non-directional nature. They can bend around large metal objects as well due to diffraction.