An introduction to the theory of dielectric loss in plastics

Perhaps the most familiar property of a dielectric material is the capacitance increase observed when a sheet of dielectric is inserted between the plates of an “air” capacitor. In fact, the ratio of dielectric to air-filled capacitance is often used to define the dielectric constant ε'. Defined in this way, its magnitude becomes a property of the material, independent of the measuring voltage or geometry of the test capacitor. The range of values for polymers is not large. The lower limit is in the neighborhood of 2 and it is rare to see one as high as 10.