RE: NEC-LIST: Ground Constants

All:

Just a gentle reminder that the ground "constants" are not constant. They
exhibit dispersion. In general, for most grounds, the relative dielectric
constant (i.e., the real part of the complex permittivity) decreases with
increasing frequency. The conductivity increases with increasing frequency.
>From DC to about 1 MHz the conductivity is essentially the DC conductivity.
So values measured at 60 Hz, as Arch Doty did some years ago to look at
trends through the seasons, are valid up to about 1 MHz. But then the
conductivity starts to increase with increasing frequency. The relative
dielectric constant for dry desert sand is about 3 to 4, and stays more or
less constant (although there is some very small fall off) as the frequency
is increased. The conductivity dominates the equations when it is much
greater than omega X epsilon. The transition from a lossy conductor to a
lossy dielectric takes place in the HF band for most soils, so both terms
tend to be important in that band.

The "handbook" values mentioned are only good in the AM broadcast band in
most cases, and one should use caution when using them at higher
frequencies.
Studies that are parametric in conductivity and assume no frequency
dependence of conductivity have an error to the extent that the
conductivity varies over the band of interest.

The best case is to be able to measure the relative dielectric constant and
conductivity at the site where you need the values, and at the time that
you need them--since they are strongly dependent on soil volumetric
mositure content.

I hope that this cautionary note is useful to some of the people on the
list.

George

Original Message:
-----------------
From: Lovestead, Ray rloveste_at_ball.com
Date: Tue, 22 Apr 2003 09:13:08 -0600
To: lemospan_at_ath.forthnet.gr, nec-list_at_gweep.ca
Subject: NEC-LIST: Ground Constants

Panayiotis P. Lemos,

This was posted to the list a couple of years ago. I find it very helpful
and
I hope others won't mind me reposting it.

Ray

From: Prof Duncan Baker

      I have received a few suggestions to add the data from the TAI Inc
Consuletter International, Vol. 6, No. 5, Earth Constants by Peter N
This was posted a couple of years ago for ground constants. I'll assume

Saveskie to the list of groundconstants. So here is the TAI list with
due acknowledgement:

Earth Type Conductivity Permittivity

                                           Sigma (Mhos/m) Epsilon

 Poor 0.001 4.0 - 5.0
 Moderate 0.003 4.0
 Average 0.005 - 0.01 10.0 - 15.0
 Good 0.01 - 0.02 4.0 - 30.0
Dry, sandy, flat (typical of coastal land) 0.002 10.0
Pastoral Hills, rich soil 0.003 - 0.01 14.0 - 20.0
Pastoral medium hils and forestation 0.004 - 0.006 13.0
Fertile land 0.002 10.0
Rich agricultural land (low hills) 0.01 15.0
Rocky land, steep hills 0.002 10.0 - 15.0
Marshy land, densely wooded 0.0075 12.0
Marshy, forested, flat 0.008 12.0
Mountainous/hilly (to about 1000 m) 0.001 5.0
Highly moist ground 0.005 - 0.02 30.0
City Industrial area of average attenuation 0.001 5.0
City industrial area of maximal attenuation 0.0004 3.0
City industrial area 0.0001 3.0
Fresh water 0.002 - 0.01 80.0 - 81.0
Fresh water at 10.0 deg C (At 100 MHz) 0.001 - 0.01 84.0
Freash water at 20.0 deg C (At 100 MHz) 0.001 - 0.01 80.0
Sea water 4.0 - 5.0 80.0 - 81.0
Sea water at 10.0 deg C (to 1.0 GHz) 4.0 - 5.0 80.0
Sea water at 20.0 deg C (to 1.0 GHz) 4.0 - 5.0 73.0
Sea ice 0.001 4.0
Polar ice 0.00025 3.0
Polar Ice Cap 0.0001 1.0
Arctic land 0.0005 3.0

-----Original Message-----
From: Panayiotis P. Lemos [mailto:lemospan_at_ath.forthnet.gr]
Sent: Monday, April 21, 2003 9:36 PM
To: nec-list_at_gweep.ca
Subject: NEC-LIST: (no subject)

Hi there
does anybody knows where am I supposed to find a table with conductivities
of
real materials?
Thanks

Panayiotis P. Lemos
Electrical & Computer Engineer, B.Sc.-M.Sc.
PhD Candidate, Hellenic Naval Academy - Chair of Electrical Engineering
IEEE EMC/APS Member
Email: lemospan_at_ath.forthnet.gr - lemospan_at_ieee.org - lemospan_at_snd.edu.gr

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