NEC-LIST: TYPO in Modeling a lLving White Pine Tree at HF

Chuck:

My apologies!! The sigma for the sap should be about 10-3 to 10-4
S/m. The volume of a dense pine grove, considered as a lossy
dielectric slab, is about 10-6 S/m. Sorry for the confusion this may
have caused.

Regards,

George

P.S. I still have to dig out my data from the experiments in Menlo
Park, CA, and in Chumporn, Thailand. So I reserve judgement for my
"final answer." And I may need a "lifeline" or two before I can
settle in on the value at HF. The conductivity has dispersion across
the HF band. This is mandated by the Cauchy integral theorem and the
Kramers-Kronig relationships based on this, which relate the real and
imaginary parts of the complex relative permittivity of the tree's
conductive layer via the Hilbert transform. A good article on this is
in the ACES Symposium Proceedings from several years ago, when the
subject was semiconductors and not trees. But trees ARE semiconductors
at HF. So can you give me a specific HF frequency, or do you want the
values vs frequency? I had some measured data at 6 and 12 MHz as well
as at about 50 MHz (as I recall, but the work was done for ARPA/CECOM
23 years ago!!).

Original Message:
-----------------
From: Chuck Counselman ccc_at_space.mit.edu
Date: Fri, 17 Nov 2000 11:41:11 -0400
Subject: Re: NEC-LIST: Modeling a living White Pine tree at HF

On Nov. 12th I wrote:
>How should a living White Pine tree be modeled at HF?

..to which George Hagn <ghagn_at_pop.mail.rcn.net> replied:
>...you could use sigma of about 10-6 S/m for the tree conductivity....

I'm bothered and confused. This (10^-6 S/m) seems an extremely low
conductivity. A tree trunk having cross-sectional area of 1 m^2 would
have a resistance per unit length (vertically) of 1 Megohm.

Is my mental arithmetic screwed up again (which it is painfully
often); are you remembering the conductivity value in some other
units; or what?

-Chuck
Received on Sun Nov 19 2000 - 19:01:24 EST