What are Piezoelectric Transducers? What is Piezoelectric Effect? working

PIEZOELECTRIC TRANSDUCER

 What is Piezo-electric effect?

A piezo-electric material is one in which an electric potential appears across certain surface of a crystals if the dimensions of the crystal are changed by the application of a mechanical force. this potential is produced by the displacement of external charges. The effect is reversible,i.e., conversely, if a varying potential is applied thereby deforming it. This effect is know as piezo-electric effect










Elements exhibiting piezo-electric qualities are sometimes known as electro-resistive elements .Common piezo-electic materials are: ammonium dihydrogen phosphate, Rochelle salts, lithium sulphate , dipotassium tartarte , potassium dihydrogen phosphate, quartz and ceramics A and B.
there are two main group of piezo- electric crystals ;
1. natural crystals....... such as quartz and tourmaline.
2. Synthetic crystals..... such as rochelle salt, lithium sulphate, dipotassium tartrate etc.

Working

A typical mode of operation of piezo-electric device employed for measuring varying force applied to a simple plate is shown in Fig.a.







 The magnitude and polarity of the induced charge on the crystal surface is proportional to the magnitude and direction of the applied force. the charge at the electrode gives rise to voltage(E) given by,

                                                        E= gtF/ A = gtp 
where g = voltage sensitivity in Vm/ N
            F= area of the crystal in m to the power 2.
            p = pressure { = F/ A} in N/ m to the power 2.








Applications of the Piezoelectric Transducers

1) The piezoelectric transducers are more useful for the dynamic measurements, i.e. the parameters that are changing at the fast rate. This is because the potential developed under the static conditions is not held by the instrument. Thus piezoelectric crystals are primarily used measurement of quantities like surface roughness, and also in accelerometers and vibration pickups.
2) For the same reasons they can be used for studying high speed phenomenon like explosions and blast waves. They are also used in aerodynamic shock tube work and seismograph (used for measurement of acceleration and vibration in rockets).
3) Many times the piezo sensors or transducers are used along with the strain gauges for measurement of force, stress, vibrations, etc.
4) The automotive companies used piezoelectric transducers to detect detonations in the engine blocks.
5) Piezoelectric transducers are used in medical treatment, sonochemistry and industrial processing equipments for monitoring the power.

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