Q: What’s a dielectric?
A: A dielectric material is an electrical insulator that becomes polarized (much like a permanent magnet) when an electric field is applied to it. A perfect dielectric would have essentially zero electrical conductance, thus only exhibiting the polarizing (displacement) characteristics.
Dielectrics are used to support/improve capacitive devices. Unlike a conductor, the electric charges do not flow through a dielectric material, since it is technically an insulator. Instead the molecules freely rearrange themselves in a highly structured order (i.e. all positives and negatives facing the same directions). This acts as a ‘useful aid’ to the conductive plates by amplifying the repulsion of negative charges. The net result is a plate on one side with a surplus of negative charges (all packed in tightly). These are attracted to the positive charges of the dielectric and a deficit of electrical charges are formed on the opposing plate due to the dielectrics negative repulsive force, resulting a net positive charge on that plate. An excellent example of this can be found online at: https://www.youtube.com/watch?time_continue=460&v=f_MZNsEqyQw
A perfect dielectric constant has a value of 1. Not zero but 1, go figure! So, any material that is fully resistant to energy therefore has a dielectric constant of 1. The only thing that meets this requirement is a vacuum because a vacuum has no material, it’s a vacuum. Therefore, air which is clean and the closes you can get to a vacuum has the lowest dielectric of 1.0006.
Next in line come the preferred cable insulations of choice. These are the three amigos, as they are infrequently called in the industry (i.e. the Teflon®’s). They have the lowest constant of all the plastics known today, barring any exotic materials reserved for government skunk-works applications. They are used not only because of their low dielectric but also because they are highly resistant to temperature and chemicals while being very stable at higher frequencies where other materials are not.
The Dielectric values are as follows:
- Low Density or Expanded (PTFE) Polytetrafluoroethylene (at 1.3),
- (PFA) Perfluoroalkoxy (at 2.0)
- (PTFE) Polytetrafluoroethylene (at 2.05)
- (FEP) Fluorinated Ethylene Propylene (at 2.1)
- (PP) Polypropylene (at 2.2)
- (PE) Polyethylene (at 2.25)
- (PVC) Polyvinyl Chloride (at 3.18)
- (PET) Polyester (at 3.3)
- Kapton® (at 3.6) but Kapton® is not good for high humidity applications since it is highly effected by humidity (i.e. water).
- (PU) Polyurethane (at 8.5)
- Note: (Kapton is a registered trademark of E. I. du Pont de Nemours and Company and Teflon is a registered trademark of the Chemours Company.)