Ground Systems
Ground analysis software

RF Skin Depth in the Ground vs. Frequency for Given Soil Characteristics

Author: R.J.Edwards G4FGQ © 18th March 1999

Alternating currents in the ground are attenuated exponentially as depth increases, like Exp(-A * Depth). Where A is an attenuation factor depending on soil resistivity R, permittivity K, and on frequency.

Skin Depth is defined as that at which the current magnitude has fallen to 36.8 percent of that at the surface. A layer of soil deeper than 4 skin depths can be considered to be of infinite thickness with respect to its top surface.

R in ohm.metres is the resistance measured between opposite faces of a 1-metre cube of the material. K is the relative permittivity obtained by measuring the capacitance between opposite faces of the cube. Therefore soil has an impedance which may be represented by a resistance in shunt with a capacitance. Impedance magnitude decreases and its negative angle increases with frequency. Values of R and K can be considered to be independent of frequency from DC to UHF.

R and K strongly depend on the moisture content of the soil and on the amounts of the various salts dissolved in it. Soils with high agricultural fertility have the lowest impedances and vice-versa. Dry rocks have very high impedances.

Typical Electrical Characteristics of Various Terrains and Soils
Terrains and Soils R
ohm/m
K
Oceans, salt seas, well away from river estuaries 0.22 81
Agricultural plains, moist, rich, highly fertile loam 30 22
Pastoral, low hills, rich soil, lawns, gardens, trees 80 15
Flat country, rivers, streams, marshes, wooded, gardens 130 12
Medium hills, forested, bushes, flowers, some clay, stones 170 12
Medium hills, heavy clay soil, weeds, grasses, mosses 250 13
Steep hills, well drained fine rocky soil, sparse vegetation 500 14
Flat, dry, sandy, some weeds, grasses, as for coastal country 500 10
Unpolluted freshwater lakes and rivers, reeds, fish, insects 1000 80
High-rise city streets, industrial areas, no vegetation 1-5,000 5
Arid sand deserts, cacti, little animal or bird life 5-20,000 3
Soil characteristics from DC to HF are relatively independent of recent rainfall.

Skin depth vs frequency for copper is computed for interest and comparison. Enter frequencies between 10 Hz and 100 MHz. Measurement units are Kilo-Hertz. Results are tabulated over a frequency range of 10-to-1. The unit of conductivity, Siemens/metre = 1/Ohm.metre, is sometimes used.

Run this Program from the Web or Download and Run it from Your Computer
This program is self-contained and ready to use. It does not require installation. Click this link SoilSkin then click Open to run from the web or Save to save the program to your hard drive. If you save it to your hard drive, double-click the file name from Windows Explorer (Right-click Start then left-click Explore to start Windows Explorer) and it will run.


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