# Piezoelectric Transducer

• A piezoelectric transducer (also known as a piezoelectric sensor) is a device that uses the piezoelectric effect to measure changes in acceleration, pressure, strain, temperature or force by converting this energy into an electrical charge.
• The piezoelectric material is one kind of transducers. When we squeeze this piezoelectric material or apply any force or pressure, the transducer converts this energy into voltage.
• This voltage is a function of the force or pressure applied to it.

## Construction

• A piezoelectric transducer consists of quartz crystal which is made from silicon and oxygen arranged in crystalline structure (SiO2).
• Generally, unit cell of all crystal is symmetrical but in piezoelectric quartz crystal, it is not.
• Piezoelectric crystals are electrically neutral.

## Working Principle

• A piezoelectric transducer is based on the principle of the piezoelectric effect.
• The word piezoelectric is derived from the Greek word piezen, which means to squeeze or press.
• The piezoelectric effect states that when mechanical stress or forces are applied on quartz crystal, produce electrical charges on the quartz crystal surface.
• The rate of charge produced will be proportional to the rate of change of mechanical stress applied to it.
• Higher will be stress higher will be voltage. • The electric voltage produced by a piezoelectric transducer can be easily measured by the voltage measuring instruments.
• Since this voltage will be a function of the force or pressure applied to it, we can infer what the force/pressure was by the voltage reading.
• In this way, physical quantities like mechanical stress or force can be measured directly by using a piezoelectric transducer.

## Piezoelectric Actuator

• One of the unique characteristics of the piezoelectric effect is that it is reversible.
• means when voltage is applied to them, they tend to change dimension along with certain plane i.e quartz crystal structure is placed into an electric field, it will deform quartz crystal by an amount proportional to the strength of the electric field.
• If the same structure is placed into an electric field with the direction of field reversed, the deformation will be the opposite. • Quartz crystal becomes longer due to the electric field applied.
• Quartz crystal becomes shorter due to the electric field applied in a reversed direction.
• It is a self-generating transducer. It does not require an electric voltage source for operation. The electric voltage produced by the piezoelectric transducer is linearly varied to applied stress or force.

## Application of Piezoelectric Materials

• In microphones, the sound pressure is converted into an electric signal and this signal is ultimately amplified to produce a louder sound.
• Automobile seat belts lock in response to a rapid deceleration is also done using a piezoelectric material.
• It is also used in medical diagnostics.
• It is used in electric lighter used in kitchens. The pressure made on piezoelectric sensor creates an electric signal which ultimately causes the flash to fire up.
• They are used for studying high-speed shock waves and blast waves.
• Used infertility treatment.
• Used in Inkjet printers
• It is also used in restaurants or airports where when a person steps near the door and the door opens automatically. In this, the concept used is when a person is near the door pressure is exerted person weight on the sensors due to which the electric effect is produced and the door opens automatically.

## Examples of Piezoelectric Materials

• Barium Titanate.
• Rochelle salt.