Mechanism of heating organic matter by radio waves

[fatherdaly]

I'm doing a study that involves radio waves passing through organic matter and have come across several sources that state that radio waves may heat organic matter when passing through it (For example: http://www.mobilfunkstudien.org/downloads/peleg_wm_10.5923.j.biophysics.20120201.01.pdf).

However, I am unclear as to the exact physical process that is causing heating. Clearly it isn't scattering since the wavelengths associated with radio waves are nowhere near the order of the diameter of organic cells. Perhaps absorption and the re-emittance? I find this unlikely too. Is it that the fields of the wave can induce a current which heats by resistive heating?

Any help would be much appreciated.

 

[SteamKing]

Think microwave oven.

 

[fatherdaly]

Think microwave oven.

Thanks! I can't believe I was being such a dunce. For clarification, this heating obviously takes energy from the wave. In doing so will the frequency of the wave be reduced (E=hf)? Thinking at a single photon level for radio waves seems a little silly.

 

[Nugatory]

Thanks! I can't believe I was being such a dunce.

Heh - I was assuming that your question was really "what exactly is the mechanism by which a microwave oven transfers energy?"

 

[fatherdaly]

Heh - I was assuming that your question was really "what exactly is the mechanism by which a microwave oven transfers energy?"

Nah, I'm just not very on the ball on mondays.

 

[Jano L.]

For clarification, this heating obviously takes energy from the wave. In doing so will the frequency of the wave be reduced (E=hf)? Thinking at a single photon level for radio waves seems a little silly.

If you do not like thinking in terms of photons, here is explanation based on electromagnetic theory: the electric field of the radio wave penetrates into the material and makes the electrons oscillate with the same frequency. Various complicated processes damp this oscillating motion, so that the oscillations have certain phase lag behind the electric field. When acting on such motion, the electric force transmits net average power to the particles and thus heats up the medium. (Kind of like when you run with some heavy things in your backpack that are not attached to it well, they will bounce around (as you make jumps running), but they will have some phase lag on average and you will feel they are slowing you down.)

 

[Drakkith]

Thanks! I can't believe I was being such a dunce. For clarification, this heating obviously takes energy from the wave. In doing so will the frequency of the wave be reduced (E=hf)? Thinking at a single photon level for radio waves seems a little silly.

No, as E=hf isn't the equation for the energy of an EM wave, it is for the energy of a single photon of a given frequency. The frequency of the wave remains the same but the energy is reduced.