• An effect exhibited by certain quartz crystals (such as lead zirconate titanates) known as ‘piezoelectric crystals’:
    • Also exhibited by certain ceramics and biological materials such as collagen and DNA
  • The piezoelectric crystal will change shape when an electrical potential is applied across it:
    • Dimensions change slightly depending upon the polarity of the applied voltage
    • Change in shape causes local changes in pressure, leading to mechanical waves (ultrasonic radiation) being generated at the exact frequency of the applied voltage
  • The converse effect occurs when pressure is applied to a piezoelectric crystal:
    • Compressive stress causes a change in dimensions of the crystal
    • Generates an output voltage at the frequency of the compressive waves
  • Allows piezoelectric crystals to act as transducers:
    • Direct effect converts mechanical energy into electrical energy
    • Converse effect converts electrical energy into mechanical energy