This is a very complex topic that refers to effective medium theories. The fact that there is more than one already tells you that the topic is very complex. I can recommend the book from A. H. Sihvola - Electromagnetic mixing formulas and applications.

The permittivity of a piezoelectric composite is a measure of its ability to store electrical charge in response to an applied electric field. The permittivity of the composite is influenced by the properties of the constituent materials, including the monomer or polymer used to disperse the piezoelectric particles.

There are several factors that can affect the permittivity of a piezoelectric composite:

It is important to consider these factors when designing a piezoelectric composite to ensure that the desired permittivity is achieved. It may also be helpful to conduct experimental testing to validate the permittivity of the composite.