The signal can be converted by piezoelectric films in many ways such as thermal to electrical (temperature sensor), mechanical to electrical (microphone), and electrical to mechanical ( a loudspeaker). The circuit is signal conditioning amplifier for piezofilm sensor which use three op amps and has a high-input-impedance differential charge. Here is the circuit :

Signal Conditioning Amplifier for Piezofilm Sensor circuit schematic

This circuit use a voltage  source  with a capacitor in series as the electrical analog  of a piezofilm sensor. The differential charge amplifier is endowed by a dual op amp (IC1)  with low supply current and single-supply operation . The input common-mode  voltage  is set by a small bypass capacitor (C3), R2, R1 at the mid-supply level. The C1 and C2 are used to set AC gain for the differential stage. A gain of C1/CEQ is 96.

The differential amplifier also is used to act as a first-order high-pass filter. The resistors R9, R8, R6, and R5 with IC2 perform differential-to-single-ended conversion. Using the values shown, the different gain is 20. [Source: maxim-ic.com]