What is the piezoelectric effect and how is it used in sensors?

Piezoelectric effect generates electrical charge when certain crystals (quartz, PZT ceramics) are mechanically stressed. In sensors, applied pressure or acceleration deforms the crystal, producing voltage proportional to the force. Piezoelectric sensors are used for dynamic pressure measurement, vibration sensing, and accelerometers. They have fast response, wide frequency range, and self-generating nature (no excitation needed), but cannot measure static/DC signals due to charge leakage.