If instead the piezo film is placed on a flexible back, (see Figure 7) and thumped with a finger a much higher (up to 200x greater) voltage is produced. The reason being the finger pressure causes the film to stretch upon impact.
To begin experimenting, there are three inexpensive piezo film transducers to choose from, PZ-01, PZ-02, and PZ-03, see figure 8. These transducers are suitable for making microphones, acoustical instrument pick-ups, piezo demonstrations, and CMOS switches. The piezoelectric material is encased in a protective urethane jacket.