Re: microwave, RF heating

[Doug Craigen <dcc@ESCAPE.CA>]

"Bernard G. Cleyet & Nancy Ann Seese" wrote:
> I don't think conductivity has anything to do with microwave absorption*.  Water is a
> rather good insulator -- Try heating a pair of glasses, one with brine, the other
> deionized water.  I'll be surprised if the temps are more different than expected due to
> variations in the microwave field with position -- you have a "carousel" oven?  Both water
> and fats, fatty acids, glycerides, etc. have O-H bonds whose stretching frequency is close
> to that of the oven's magnetron.  Amino acids, and, therefore, proteins, also have OH
> bonds (in the carboxylic group), so they heat up too.  I would expect the heating to be
> some monotonically increasing function of the density of OH bonds.  I'll ask my
> nutritionist friend about the comparative densities in egg yolk and white.

Bond stretching is in the IR range.  Microwave spectra are associated
with molecular rotations, which is why liquids and gases tend to absorb
microwaves better than solids.  For gases there are well defined
absorption lines, but the denser the gas the broader the peak due to
neighbor interactions.  If a "gas" is dense enough to be "liquid" you
expect a very broad featureless peak.


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Doug Craigen
          http://www.dctech.com/physics/