The electrical behavior of an unstressed medium under the influence of an electric field is defined by relationship (1) of the field strength E and the dielectric displacement
D (there [epsilon]--the permittivity of medium).
Eventually, the return via is no longer used for any significant amount of return current, and all the return current flows though the dielectric displacement
current (and the return via has no impact in the inductance the signal experiences).
Direct Piezoelectric Effect: When a force is applied to a piezoelectric material, surface charges are induced by the dielectric displacement
, and therefore an electric field is built up.