Piezoelectric Transducer: Applications & Working Principle

What is 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.

A transducer can be anything which converts one form of energy to another. 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.

The electric voltage produced by a piezoelectric transducer can be easily measured by 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.

What is Piezoelectric Transducer

Piezoelectric Actuator

A piezoelectric actuator behaves in the reverse manner of the piezoelectric sensor. It is the one in which the electric effect will cause the material to deform i.e. stretch or bend.

That means in piezoelectric sensor, when force is applied to stretch or bend it, an electric potential is generated and in opposite when on a piezoelectric actuator, an electric potential is applied it is deformed i.e. stretched or bend.

Piezoelectric Actuator

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

The atoms inside them may not be symmetrically arranged but their electrical charges are balanced means positive charges cancel out negative charge. The quartz crystal has the unique property of generating electrical polarity when mechanical stress applied on it along a certain plane. Basically, There are two types of stress. One is compressive stress and other is tensile stress.

Piezoelectric Quartz

When there is unstressed quartz no charges induce on it. In the case of compressive stress, positive charges are induced in one side and negative charges are induced in the opposite side. The crystal size gets thinner and longer due to compressive stress. In the case of tensile stress, charges are induced in reverse as compare to compressive stress and quartz crystal gets shorter and fatter.

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 piezoelectric effect is discovered by Pierre and Jacques Curie. 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.

One of the unique characteristics of piezoelectric effect is that it is reversible means when voltage is applied to them, they tend to change dimension along certain plane i.e quartz crystal structure is placed into an electric field, it will deform quartz crystal by amount proportional to strength of electric field. If same structure is placed into an electric field with direction of field reversed, the deformation will be opposite.

Piezoelectric Effect

Quartz crystal becomes longer due to electric field applied

Piezoelectric Sensor

Quartz crystal becomes shorter due to electric field applied in reversed direction.
It is self-generating transducer. It does not require electric voltage source for operation. The electric voltage produced by piezoelectric transduce is linearly varies to applied stress or force.

Piezoelectric transducer has high sensitivity. So, it acts as sensor and used in accelero meter due to its excellent frequency of response. The piezoelectric effect is used in many application that involve production and detection of sound, electronic frequency generation. It acts as ignition source for cigarette lighter and used in sonar, microphone, force, pressure and displacement measurement

Application of Piezoelectric Materials

Using piezoelectric materials, piezoelectric transducers can be used in a variety of applications, including:

  1. In microphones, the sound pressure is converted into electric signal and this signal is ultimately amplified to produce louder sound.
  2. Automobile seat belts lock in response to a rapid deceleration is also done using piezoelectric material.
  3. It is also used in medical diagnostics.
  4. It is used in electric lighter used in kitchens. Pressure made on piezoelectric sensor creates an electric signal which ultimately causes flash to fire up.
  5. They are used for studying high speed shock waves and blast waves.
  6. Used in fertility treatment.
  7. Used in Inkjet printers
  8. 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 person is near the door a pressure is exerted persons weight on the sensors due to which the electric effect is produced and the door opens automatically.

Examples of Piezoelectric Material

The materials are :

  1. Barium Titanate.
  2. Lead zirconate titanate (PZT).
  3. Rochelle salt.

The Piezoelectric Ultrasonic Transducer

It produces frequencies which are far above than that which can be heard by the human ear. It expands and contracts rapidly when subjected to any voltage. It is typically used in vacuum cleaner.

Piezo Buzzer

A buzzer is anything which produces sound. They are driven by the oscillating electronic circuit. A piezoelectric element may be driven by an oscillating electronic circuit or another audio signal source, driven with a piezoelectric audio amplifier. A blick, a ring, or a beep are commonly sued sound to indicate that a button has been pressed.

A piezoelectric buzzer (or piezoelectric beeper) depends on acoustic cavity resonance (or Helmholtz resonance) to produce an audible beep.

Piezoelectric Transducer Advantages

The advantages of piezoelectric transducers are:

  1. No need of external force
  2. Easy to handle and use as it has small dimensions
  3. High-frequency response it means the parameters change very rapidly

Piezoelectric Transducer Disadvantages

The disadvantages of piezoelectric transducers are:

  1. It is not suitable for measurement in static condition
  2. It is affected by temperatures
  3. Output is low so some external circuit is attached to it
  4. It is very difficult to give desired shape to this material and also desired strength

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