Charge Conservation, Piezoelectric
This feature is available with the Piezoelectricity interface, which requires the Acoustics Module, MEMS Module, or the Structural Mechanics Module. See the individual documentation for information.
The Charge Conservation, Piezoelectric node is normally used together with a Piezoelectric Effect multiphysics coupling node and a corresponding Piezoelectric Material node in the Solid Mechanics interface. The node is added by default to the Electrostatics interface when adding a Piezoelectricity interface. It is also available from the context menu (right-click the Electrostatics interface parent node) or from the Physics toolbar.
When the Charge Conservation, Piezoelectric node is added to the electrostatics interface in the absence of an active Piezoelectric Effect multiphysics coupling node, the material behaves similarly to a Charge Conservation node, with electric properties corresponding to the relative permittivity entered (see below). The piezoelectric effect is not included in the corresponding equation system.
Electric Displacement
If the node is used together with an active Piezoelectric Effect multiphysics coupling node, then these settings are locked. Note that if they are unlocked, then the material behaves like a dielectric and not a piezoelectric. In this case, the default is to take the Relative permittivity εrS (dimensionless) values From material.  For User defined, select Isotropic, Diagonal, Symmetric, or Full and enter values or expressions in the field or matrix.