Yes- A vacuum is the best. BUT- Containing vacuums and gases is tricky/expensive, and therefore not often practical (http://www.taralabs.com/images/31479_eprint.pdf). Some manufacturers create a foam of a plastic and air which does work well. Teflon is usually considered the best(after vacuum/air/distance) in any dielectric application.
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natural unbleached cotton is closest to air in dielectric constant. That is a common misconception because people google dielectric constant and wind up here: http://www.asiinstr.com/technical/Dielectric%20Constants.htm a company that makes instruments for measuring bulk solids, the number given is for raw cotton very much like a cotton ball and has a high ration of air to solid. This is a much more relative site for finding information on cotton as used in our field: A Swiss textile company: http://www.swicofil.com/products/001cotton.html#Properties as you can see the dc for cotton made into a usable form, similar to what would be covering a wire is between: 3.9 7.5 what cotton does do well is reduce mechanical vibration which is why it is used frequently as a cable filler. It is also hydrophilic which is not something you want next to a metal conductor. Microporous PTFE & PE and solid PTFE is for all practical purposes the best dielectrics to use. A tube filled with nitrogen would be great but not very practical to manufacture, a vacuum even less so. |
Ah, but a tube filled with liquid nitrogen would be even more intriguing, especially if the wire it surrounded was made from one of the high-temp superconductors. Imagine the look on your buddies faces when you topped up the liquid nitrogen in your cables before your local audio club's next listening session! Mmwaaahaahaahaa! |
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