Typical Values for Rocks and Other Materials
The range of relative permittivities for rocks and other materials is tabulated below. Also included are: the average propagation velocity (\(V_{avg}\)) of radiowave signals, the conductivity (\(\sigma\)) and the approximate penetration depth of radiowave signals; these are relevant to ground penetrating radar.
Rocks within a certain classification vary significantly in composition. As a result, particular rock types made be characterized using a range of relative permittivities. By examining the table below, several things can be inferred:
Water has a much higher dielectric permittivity than rock forming minerals.
Water saturated rocks have larger dielectric permittivities than dry rocks.
Saturated sediments generally have larger dielectric permittivities than hard rocks.
The variation in dielectric permittivity for sediments is larger than it is for hard rocks.
The combination of conductive and dielectric properties for each material results in significant variations in penetration depth for radiowave signals.
Material |
\(\varepsilon_r\) |
\(V_{avg}\) (m/ns) |
\(\sigma\) (ms/m) |
Penetration Depth (m) |
|---|---|---|---|---|
Air |
1 |
0.3 |
0 |
\(\infty\) |
Fresh Water |
80 |
0.033 |
0.5 |
285 |
Sea Water |
80 |
0.01 |
3000 |
< 0.1 |
Ice |
3 - 4 |
0.16 |
0.01 |
3000 |
Dry Sand |
3 - 5 |
0.15 |
0.01 |
3200 |
Saturated Sand |
20 - 30 |
0.06 |
0.1 - 1 |
145 |
Limestone |
4 - 8 |
0.12 |
0.5 - 2 |
30 |
Shales |
5 - 15 |
0.09 |
1 - 100 |
1 |
Silts |
5 - 30 |
0.07 |
1 - 100 |
1.3 |
Clays |
5 - 40 |
0.06 |
2 - 1000 |
0.2 |
Granite |
4 - 6 |
0.13 |
0.01 - 1 |
65 |
Anhydrites |
3 - 4 |
0.13 |
0.01 - 1 |
55 |