Re: Superdialectrics? (fwd)
---------- Forwarded message ----------
Date: Wed, 22 Apr 1998 22:59:33 +0300
From: Harri Suomalainen <haba-at-cc.hut.fi>
Subject: Re: Superdialectrics?
>superconductors. Also, I've noticed that there is a general
>correspondence between losses and the dialectric constant
>of certain materials. Someone on this list mentioned that this
>is because of polar molecules that cause friction when aligning.
I mentioned that. I should perhaps emphasize that real alingment
does indeed exist when the frequency is low enough so that the
molecules (or parts of them) have time to rotate. At higher
frequency there is no time for complete or perhaps even partial
rotation or alignment and the effect will be more like vibration.
I have seen this documented in the literature too.
Losses tend to go up with high dielectretic constants, you got that
right. However, I've not seen it documented anywhere. (Haven't
really tried to find that either.) The idea of small microscopic rotations
causing something like friction is entirely my own. It is just hypothesis
with which I'm able to see the things better.
>That got me to thinking- are there such things as "superdialectrics"?
>That is, are there materials, where at a certain temperature, the
>lose all resistance to aligning, and hence, no losses? You could then use
>a material with an insane dialectric constant, 60-80 maybe.
60-80 insane? :) Uhum, materials with dielectretic constant in the order
of *hundreds* do exist. However, to have high dielectretic constant you
need a lot of charge to be displaced in the dielectretic. So, very polar
molecyles are preferred. That's why ionic compounds (crystals) like
barium titanate have very high dielectric constants.
Low-loss materials would need either low vibrations/rotations or enough
room around the molecules that no friction effects would occur.
that does mean you need low polarity for low vibrations. To get more space
for the particles you'd need to take them apart. However, when they are
closely interacting with each others they are usually better known as
or gases. Displaceable charge per unit volume decreases in that case a lot
ie. dielectretic constant goes down.
Unfortunately, I see no way for such wonder-material. Not that I wouldn't
like to have low-loss 1uF/100kV caps the size of a matchbox. :) :) :)
Harri Suomalainen mailto:haba-at-cc.hut.fi
We have phone numbers, why'd we need IP-numbers? - a person in a bus