A piezoelectric material is one in which as electric pressure appears across certain surfaces of a crystal if the dimensions of the crystal are changed by the application of a mechanical force. The effect is reversible, i.e. conversely, if a varying potential is applied to the proper axis of the crystal, it will change the dimensions of the crystal thereby deforming it. This effect is known as piezoelectric effect. Piezoelectric transducers do not need any external power source and is, therefore, known as active transducers.
The piezoelectric effect can be made to respond to (or cause) mechanical deformations of the material in many different modes. The modes can be : thickness expansion, transverse expansion, thickness shear and face shear.
A piezoelectric element used for converting mechanical motion to electrical signals.
In these transducers, a crystal is placed between a solid base and the force summing member. When an external force, entering the transducer through its pressure port, applied pressure at the top of the crystal, this produces an e.m.f. across the crystal. The magnitude of the induced e.m.f. is proportional to the magnitude of the applied pressure. Since the induced e.m.f. is very small of the order of millivolts, an amplifier is used to amplify this e.m.f. signal being measured.
Piezoelectric transducers do not need any external power source and is, therefore, known as active transducers.
Common piezoelectric materials include Rochelle salts, ammonium dihydrogen phosphate, lithium sulphate, quartz and ceramics. Except for quartz and ceramics, the rest are man-made crystal grown from aqueous solutions under carefully controlled conditions.