[AMPS] Properties of plastics at 10 GHz

[Geurts, Gerard]

Rich wrote:

> >- - - To check it out, put a styrene cup half full of water, 
> >along with a sample of the plastic you want test, in a microwave oven
> and 
> >blast away for a dozen or so seconds.
> 
Jon replied:

> Ever notice that when you put a styrene cup of water in the microwave 
> that the water gets hot but the styrene doesn't.  It certainly can't
> be 
> because the styrene is "absorbing" the energy and then by conduction 
> heating the water.  No, the styrene doesn't get hot because it PASSES
> all 
> the energy that goes through it.  The heating that takes place is the 
> interaction of the microwave energy with the water molecules making
> the 
> molecules vibrate and thereby producing heat.  With a lot of energy 
> applied to it an abosrptive material will get hot just like your dummy
> 
> load.  So if the styrene material absorbed enough energy to make a cup
> of 
> water boil, it would melt.  It would certainly have to be much hotter 
> than the boiling point of water even if it DID absorb energy.  Heat 
> transfer to the water would be very inefficient as the water would
> give 
> off heat to the air as well as the styrofoam.  So in order to get a
> high 
> enough temperature like that you'd heat the styrene past melting
> point.
> 
> Rich, I hate to say it but you are incorrect on this one.
> 
I hate to say it, but Rich is right on this one. The problem very often
is that Jon does not read the original messages properly. In this case,
Rich never said that the styrofoam heats up. The cup with water is a
dummy load to make sure the microwave can get rid of its energy
somewhere. Rich writes: 'put a styrene cup half full of water, along
with a sample of the plastic you want test, in a microwave oven and
blast away for a dozen or so seconds.' Notice Jon that Rich talks about
a cup of water AND a sample of the material you want to test. Read and
understand the message before you hit the send button next time you want
to impress us with your superior knowledge.

Gerard, AA3ES

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