Construction and working of Piezo-electric Generator

 Construction

The circuit diagram is shown in figure

The quartz crystal is placed between two metal plates A and B. The plates are connected to the primary (L3) of a transformer which is inductively coupled to the electronics oscillator.

The electronic oscillator circuit is a base tuned oscillator circuit.

The coils L, and L, of oscillator circuit are taken from the secondary of a transformer T.

The collector coil L2 is inductively coupled to base coil Lj.

The coil L, and variable capacitor C, form the tank circuit of the oscillator.

Working

When H.T. battery is switched on, the oscillator produces high frequency alternating voltages with a frequency.

Due to the transformer action, an oscillatory e.m.f. is induced in the coil Lz. This high frequency alternating voltages are fed on the plates A and B.

Inverse piezo-electric effect takes place and the crystal contracts and expands alternatively. The crystal is set into mechanical vibrations.

The frequency of the vibration is given by

The variable condenser C, is adjusted such that the
frequency of the applied AC voltage is equal to the natural frequency of the quartz crystal, and thus resonance takes place.

The vibrating crystal produces longitudinal ultrasonic waves of large amplitude.