Permittivity of Some Common Materials
The values below are relative permittivity
for a few materials that are commonly encountered in electrical engineering applications, and for which permittivity emerges as a consideration. Note that “relative permittivity” is sometimes referred to as dielectric constant.
Here we consider only the physical (real-valued) permittivity, which is the real part of the complex permittivity (typically indicated as
) for materials exhibiting significant loss.
Permittivity varies significantly as a function of frequency. The values below are representative of frequencies from a few kHz to about 1 GHz. The values given are also representative of optical frequencies for materials such as silica that are used in optical applications. Permittivity also varies as a function of temperature. In applications where precision better than about 10% is required, primary references accounting for frequency and temperature should be consulted. The values presented here are gathered from a variety of references, including those indicated in “Additional References.”
Free Space (vacuum):
|Rogers RO3003||3.0||PCB substrate|
|FR4 (glass epoxy laminate)||4.5||PCB substrate|
1Properly known as extruded polystyrene foam (XPS).
2Properly known as polytetrafluoroethylene (PTFE).
3Typically doped with small amounts of other materials to slightly raise or lower the index of refraction (
Non-conducting spacing materials used in discrete capacitors exhibit
ranging from about 5 to 50.
- Semiconductors commonly appearing in electronics – including carbon, silicon, geranium, indium phosphide, and so on – typically exhibit in the range 5–15.
- Glass exhibits in the range 4–10, depending on composition.
- Gasses, including air, typically exhibit to within a tiny fraction of a percent.
- Liquid water typically exhibits in the range 72–81. Distilled water exhibits at room temperature, whereas sea water tends to be at the lower end of the range.
- Other liquids typically exhibit in the range 10–90, with considerable variation as a function of temperature and frequency. Animal flesh and blood consists primarily of liquid matter and so also exhibits permittivity in this range.
- Soil typically exhibits in the range 2.5–3.5 when dry and higher when wet. The permittivity of soil varies considerably depending on composition.
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