A piezoelectric material is one in which an electric potential appears across certain surfaces of a crystal if the dimensions of the crystal are changed by the application of a mechanical force. This potential is produced by the displacement of charges. 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 deforms it. This effect is known as piezoelectric effect. Piezoelectric materials include Rochelle salts, Ammonium dihydrogen phosphate, lithium sulphate, dipotassium tactarate, potassium dihydrogen phosphate, quartz andceramics A & B.

When a force F is applied to a piezoelectric crystal it develops a charge d = dF Coulomb where d = charge sensitivity of crystal; C/N. Through incorporation of mass, m1 in direct contact with the crystal, we have the essential components of an acceleration transducer. By applying a varying acceleration to the mass- crystal assembly, the crystal experiences a varying force. The force is given by F = ma where a = acceleration This force generates a varying charge Q = dF = dMa Suppose the crystal has a capacitance, C, the no load output voltage is, eo = Q/C = dF/C = d Ma/C

Therefore the output voltage is a measure of the acceleration

The piezoelectric crystal is spring loaded with seismic mass in contact with crystal, when subjected to an acceleration, the seismic mass stresses the crystal to a force F = Ma, resulting in a voltage generated across the crystal. The forces generate an output voltage which is proportional to the acceleration.

Advantages: 1. Small in size and has a small weight. 2. Natural frequency is very high and therefore the accelerometer is useful for high frequency. It can be used for any vibration & shock application. 3. The crystal is a source with high output impedance and in order to avoid loading effect, a voltage monitoring source of high input impedance should be used.