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Dielectric Const.

 

Dielectric Constant (K) "Typical"

 

          Table 14 shows the approximate dielectric constants of a variety of materials, including capacitor dielectrics, and coax cable insulations.  These are rough averages of numbers from several handbooks and various manufacturers' literature, which often disagree significantly.  Most are for 25C but some are at 20C.

table 14
table14a

1 Dupont, epoxy w/ aramid paper
2 epoxy/bismaleimide triazine blend
3 Specialty Coating Systems, Div. of  Alpha Metals
4  These values are nominal, a given ceramic can have a range of Ks.  Ceramic capacitor classes represent performance specifications, not specific formulas.  Manufacturers can meet those specifications any way they like, depending on which parameter they might wish to enhance at the expense of others.  They can also brew up dielectrics that don't exactly correspond to any EIA type.  As mentioned elsewhere, the lower the K for a given type of dielectric, the better the overall performance tends to be, so the usual tradeoff is size vs. everything else.  This is not of concern to most users, but it can be for people who use large ceramics in high-power RF applications like switching power supplies or radio transmitters.  For them, size vs. dissipation factor may be very important.  The range of Ks for common ceramic dielectrics is shown in table 15.

table 15

5  Varies somewhat by exact resin content; the more resin, the lower the K.

6   Cheap shielded cables are often made with this stuff, but these are only suitable for audio frequencies or low rate data communications.   Quality data cable will generally be made with polyethylene inner insulation to minimize capacitance, or better yet, cellular polyethylene, which is about 50% air. 

          Also see http://www.asiinstr.com/dc1.html