Page 67 - Semester-IV-Electronics

 Frequency of vibrations due to piezoelectric effect depends on

dimensions of crystal and the way of cutting it.

 The piezoelectric crystal plates obtained from hexagonal shaped

quartz crystals are cut in such a way that effect of temperature

variation on the natural frequency is minimum and desired natural

frequency is obtained.

 Electrodes on opposite faces of a piezoelectric crystal are made by

electrical plating on which appropriate alternating potential is

applied.

 Crystal mechanically vibrates and when frequency of alternating

voltage becomes equal to natural frequency of the crystal, amplitude

of mechanical vibrations becomes maximum.

 Resonant frequencies from 10 kHz to 10 MHz can be achieved.

 Crystal having induced vibrations by alternating potential can be

represented by a series LCR circuit shunted by capacitance C`

between electrodes of the crystal.

67