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[TowerTalk] tree conductivity

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Subject: [TowerTalk] tree conductivity
From: Jim Lux <>
Date: Wed, 28 Dec 2011 10:20:51 -0800
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I'm looking around for data on electromagnetic properties of trees 
(mostly electrical.. I don't think trees have any appreciable magnetic 

I found this interesting reference where they measure tree conductivity 
to find soil contaminants
but no numbers

A paper by some Israeli researchers (Nadler, et al) found some 
correlation between water salinity and soil and tree conductivity (for 
grapefruit trees)..Using TDR for the measurement they reported tree stem 
conductivity (no leaves) of 0.01 to 0.08 dS/m  (deciSiemens, I assume). 
  They've got tons of pubs out there I'm looking through.

Some older works (1914, 1920) seem to indicate that there isn't much 
change in conductivity as a result of sap running or not (e.g. not much 
seasonal variation in conductivity of the stems/branches/tree trunks)

There's a thing called a shigometer which is basically a ohmmeter using 
two probes stuck into the tree.  But it's hard to relate data from that 
to general material properties.

An Italian group (Sambuelli, et al) did a fairly decent report on 
Ultrasonic, Electric and Radar Measurement for Living Trees Assessment 
(this is a popular topic.. is that 60 year old tree next to the road 
about to collapse because it's rotten at the core?)

Even better, these folks did measurements from 10 Hz to 10MHz using a 
network analyzer.. Interestingly, the resistivity goes DOWN as a 
function of frequency (that is, at 10 MHz the resistivity is like a 
tenth of what it is at 1 kHz).  (the change is even more dramatic for 
dry wood... many orders of magnitude).  Ditto for permittivity... huge 
change between permittivity at 10 kHz and 10 MHz (for wood with 35.5% 
moisture, 250 at 10kHz, 10 at 10 MHz)

(this means that looking up wood electrical properties in a handbook 
where they make the measurements at 50 or 60Hz is not particularly 
useful for us)

based on the Italian paper, I'd say assuming a relative permittivity of 
5-10 and a resitivity of 50-100 ohm meter for living wood would be 
reasonable.  (50-100 ohm meter resitivity =  20-10 mS/m conductivity)

Or, in other words, trees aren't much different than the soil properties 
we use in modeling (e.g. 5mS/m, epsilon 13 for "good").

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