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I'm wondering what the dielectric constant or permittivity of metals is --particularly copper. Do metals have an infinite permittivity?

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You can look this up on the internet. At low frequencies metals have large permittivity as shown here. However, since you mention COMSOL I wonder if you're working at higher frequencies, in which case I would suggest looking up real data. – DanielSank Jan 9 at 19:42
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In electromagnetism, absolute permittivity is the measure of the resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium.

Yes, metals have infinite permittivity as they completely negate the electric field inside their bulk. I.e. infinite resistance to setting up of field and hence infinite permittivity. But this case is more valid for perfect conductors as realistic conductors would have defects and impurities.

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Thanks. Since I have to specify the permittivity of copper in my COMSOL simulation with a constant number. Can I just use a big number? Is 1e10 large enough to express the permittivity of a metal? – Ali Abbasinasab Jan 13 '14 at 22:45
Yes definitely, the impurities only bring about minor deviations from idealistic behaviour, if it wasn't so electric shielding would not be realisitic and Faraday Cages would not be a real thing. :) – Rijul Gupta Jan 13 '14 at 22:48
Woah, what?! Metals do not have infinite permittivity when you are dealing with signals at nonzero frequency, and this definitely matters in applications. – DanielSank Jan 9 at 19:39

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