Re: NEC.LIST: Ground, water, and fields

At 1:47 PM 96.10.13 -0700, w7el_at_teleport.com wrote:

w7el>At DC, water is quite non-conductive and has a high dielectric constant. At
w7el>RF, it's lossy, ......... skipped .........
w7el>conductivity is determined by mechanisms other than those causing ordinary
w7el>DC resistance.

 The dielectric constant of water is basically determined by the electrical
dipole of
the molecule. (H+)(O-)(H+) structure is not straight (108deg?).
When RF field is applied, its kinetic movement cannot quite follow the field,
hence loss is produced. So, this loss should be interpreted as imaginary part of
the dielectric constant of water, and not as conductivity.
Also, the loss tangent is freq. dependent.

w7el>Because of the mechanism by which the loss occurs, it
w7el>doesn't seem unreasonable to think that the apparent conductivity might be
w7el>different when interacting with magnetic and electric fields -- perhaps
w7el>very different.

yes, it should be very different. The above mechanism tells that there is
no interaction with magnetic field.

w7el>....., a single set of conductivity and dielectric constant
w7el>values might not be adequate for NEC ground specification, but some sort of
w7el>field-sensitive value might be required instead.

I believe it was wise that NEC chose a single set.
However, proper numbers should be used for each freq. of analysis.

w7el> ....... Of course, ground water
w7el>contains dissolved salts and so has non-zero DC conductivity, which may (or
w7el>may not) dominate and swamp any field-sensitive effects.

A friend told me that, sea water is lossy when seen as a dielectric material,
but is low loss when used as a reflective plane, because the two has different
mechanism of producing loss (which I don't know much about).

I wrote only what I know.
It is suggested to contact material and/or physic people, for detail, and for
more reliable information. (I am not any expert on this.)

Hideho Yamamura / JF1DMQ, AA6VE
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Hideho YAMAMURA, hyamamu_at_kanagawa.hitachi.co.jp
Hitachi, Ltd., Japan
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Received on Tue Oct 22 1996 - 08:36:37 EDT