**3.1. Polymer matrix: PVDF**

PVDF is a piezoelectric polymer (d33= –33 pC/N) that is able to produce variation in the surface charge when subjected to mechanical stress without requiring additional energy sources or electrodes for the generation of electrical signal. This polymer consists of a carbon-based chain with alternating hydrogen and fluorine units (–CH2–CF2–)n, and its molecular weight is around 105 g.mol–1. PVDF presents polymorphism and can be found in four structural phases (α, β, γ and δ) where the piezoelectric phase is said to be the β phase once it is a polar phase [8,32].
