Hello, readers here today we know about the **direct and inverse piezoelectric effect of ultrasound**, piezoelectric method for produce ultrasonic sounds.

## Piezoelectric effect:

when pressure is applied to one pair of opposite faces of crystals like Quartz, tourmaline, Rochelle salt etc, cut with their faces perpendicular to its optic axis, equal and opposite charges appear across its other faces as shown in fig. this is known as the piezoelectric effect.

## Inverse piezoelectric effect:

If an alternating voltage is applied to one pair of opposite faces of the crystal, alternatively mechanical contractions and expansions are produced in the crystal and the crystal starts vibrating. This effect is known as * inverse piezoelectric effect* or electrostriction effect.if want to know More read this – piezoelectricity

- – When the frequency of the applied alternating voltage is equal to the vibrating frequency of the crystal, then the crystal will produce ultrasonic waves.

##### Construction

The experimental arrangement is shown in fig. Quartz crystal Q is placed between two metal plates A and B, connected to the coil 1-3. The coil 1-1, 1-2 and 1-3 are inductively coupled to each other. Coil I-I is connected parallel with variable capacitor CI forming the tank circuit. Coil L2 is connected to the collector output of the transistor. The high tension battery is connected between the free end of 1-2 and the emitter of the transistor.

##### Working:

When high tension battery is switched on, frequency alternating voltage is given by

f = 1/2π√L√C

The f of oscillation can be controlled by the variable capacitor Cl.

Due to the transformer action, an emf is induced in the secondary coil 1-3. This emf is impressed on the plates A and B, will excite the quartz crystal into vibrations. By adjusting the variable capacitor Cl, the frequency can be achieved in resonant conditions and crystal will produce ultrasonic waves. The frequency of vibrations is

f = 1/2l √E/¶

Where, E is Young’s modulus, ¶ is the density of the material, I is the length.

###### Merits:

– More efficient

– frequency can be achieved up to 5 x IOA8 Hz

– o/p of this oscillator is very high.

– not affected by temperature and humidity

###### Demerits:

– cost is high and crystal’s cutting and shaping are very complex.

hope you guys happy to read about direct and inverse piezoelectric effect of ultrasound and if you have any doubt than comment below.