Typical Values for Rocks and Other MaterialsΒΆ
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 | 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 |