Permittivity converter
Convert a material’s permittivity between εr, F/m, susceptibility and cable velocity factor.
That's about the same as FR-4 circuit board. A signal in it travels at about 47.67% of the speed of light.
What it means
How strongly does it polarize?
Values are typical at low frequency and room temperature. Water’s permittivity falls sharply at microwave frequencies, which is how microwave ovens heat it.
Every unit
Your permittivity in every unit
Learn
Three things worth knowing
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Signals slow by √εr
In PTFE at 2.1 a signal runs at 69% of light speed; in FR-4 board at 4.4, about 48%. That is the cable’s velocity factor.
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Faraday’s specific inductive capacity
Michael Faraday found in 1837 that filling a capacitor with shellac or glass stored more charge. He called it specific inductive capacity; we call it the dielectric constant.
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High is not always good
Water’s εr of 80 makes great capacitors in theory, but it leaks and absorbs radio energy. Low-permittivity insulators like PTFE are prized precisely because they get out of the signal’s way.
Shortcuts
Popular permittivity conversions
Background
About permittivity
Permittivity says how much a material weakens an electric field by lining up its own charges against it. Relative to a vacuum it is the dielectric constant, εr: 1 for vacuum, about 4 for circuit-board glass-epoxy, 80 for water.
It sets how much a capacitor holds, and how fast a signal runs along a cable: a wave slows by √εr.