🚀 go-pugleaf

An excellent followup to my article!

ornitz@kodak.kodak.com (Barry Ornitz) writes:
>alex@bilver.uucp (Alex Matulich) writes:
>>When I was doing radar testing of materials at General Dynamics some years
>>back, we did transmission testing of water.  I can't say that the higher
>>attenuation we observed at approx. 2 GHz was a "resonant frequency" but it
>>was certainly an absorbtion frequency.
>
>You are on the right track, but I believe your memory is somewhat faulty.
>Water is a good absorber over an EXTREMELY broad frequency range.  In terms of

I know that, we characterized it from .5 GHz to 18 GHz.  Pretty flat
except around 2 GHz, which is why I said what I said.

It is possible that there was a fault with our measurement, because the 2
GHz range was at one end of two different testable bandwidths for us
(we needed different equipment above and below).

>You are correct about dielectric constants.  Von Hippel's various books on
>dielectrics give graphs of the complex permittivity of water as a function of
>frequency and temperature.  [Permittivity is the correct term - the dielectric

Ah, Von Hippel was our bible!  Every time we developed a new material
measurement system, or analytical method, we always checked against Von
Hippel's results.  Amazingly, we did find a few inaccuracies in his data
here and there.  Can't remember what they were offhand; this was 4 years
ago.

>more uniform heating.  Home ovens are far from uniform as you can easily
>demonstrate with a plate full or marshmellows!

Or a bowl of butter cubes!  Or a tray of raw cookies!  My mother once
accidentally burned some cookies in the microwave.  We turned all the
cookies over at once to reveal their undersides, and then looked at the
array of cookies.  Dark burn lines were visible, radiating outward from the
general center of the cookie array.  That's something that you wouldn't
expect from a conventional oven.

>To summarize - home microwave ovens operate at the frequency they do because
>of a number of factors: engineering, economics, dielectric properties, and
>politics - not because of any special resonant absorption phenomena.

Agreed.

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