Mike Kaliski wrote:

"Chuck" wrote in message
...
Mike Kaliski wrote:


Commercial microwave ovens have always worked on the principle of
heating
water by being tuned to the vibrational frequency of water molecules.


Hmmm. The first resonant peak of the
water molecule is around 1THz, while at
the microwave operating frequency of
2.45GHz there are no resonances of the
water molecule.

The 2.45GHz frequency has no particular
connection to the resonant frequencies
of candidate food molecules.

Chuck

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Chuck

That would be why returns on 3 Cm marine radar are wiped out in heavy rain
then. I can vouch for the fact that heavy rain and spray can result in 100%
obscuration of ship radar targets.

Aircraft also use radar to detect storms. The severity of the weather ahead
is determined by analysis of the probable size of the water droplets in the
cloud, which affects the level of the radar return.

While water molecules may have an inherent resonance at 1 THz, it is
generally accepted by the scientific community that microwave ovens work by
exciting water molecules, amongst others, in food. I can't recall ever
cooking anything in a microwave that wasn't wet or at least damp. Well I
have tested some bits of plastic for suitability for use at RF, but that
wasn't for eating - and the wife was out!!!

I am happy to accept that there is no direct correlation between the
resonant frequency of a water molecule at 1 THz and a microwave oven
magnetron operating in the Ghz range. However, microwave ovens will heat
even distilled water quite effectively and heating is defined as an increase
in vibrational energy of molecules. So however the process actually works,
some principle of resonance must exist to allow the excitation of the water
molecules to occur. Either that, or microwave ovens actually work by heating
the food with infra red radiation derived using waste heat from the
magnetron and we have all been fooled. :-)

Mike G0ULI

You can look at the stuff in a microwave as a resistive load.

What happens to a resistive load when you feed it RF?

Or even DC, but putting in all the little DC probes so the burrito heats
evenly is a pain in the butt.



--
Jim Pennino

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