Piezo-electric transducer-Biosensors and Transducers

Piezo-electric transducer-Biosensors and Transducers

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  PIEZOELECTRIC TRANSDUCER MUKESH SUNDARARAJAN
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  PIEZOELECTRIC EFFECT • Thereare certain materials that generate electric potential or voltage when mechanical strain is applied to them or conversely when the voltage is applied to them, they tend to change the dimensions along certain plane. This effect is called as the PIEZOELECTRIC EFFECT. This effect was discovered in the year 1880 by Pierre and Jacques Curie.
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  PIEZOELECTRIC TRANSDUCERS • Thepiezoelectric transducers work on the principle of PIEZOELECTRIC EFFECT . When mechanical stress or forces are applied to some materials along certain planes, they produce electric voltage. This electric voltage can be measured easily by the voltage measuring instruments, which can be used to measure the stress or force. A piezoelectric disk generates a voltage when deformed (change in shape is greatly exaggerated)
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  • The voltageoutput obtained from the materials due to piezoelectric effect is very small and it has high impedance. To measure the output some amplifiers, auxiliary circuit and the connecting cables are required. symbol
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  Materials used forthe Piezoelectric Transducers • There are various materials that exhibit piezoelectric effec. The materials used for the measurement purpose should posses desirable properties like • stability, • high output, • insensitive to the extreme temperature and humidity and • ability to be formed or machined into any shape. • But none of the materials exhibiting piezoelectric effect possesses all the properties.
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  Examples of PiezoelectricMaterial The materials are : • Barium Titanate. • Lead zirconate titanate (PZT). • Rochelle salt. • Quartz
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  and WORKING •The figure showsa conventional CONSTRUCTION piezoelectric transducer with a piezoelectric crystal inserted between a solid base and the force summing member. • If a force is applied on the pressure port, the same force will fall on the force summing member. • Thus a potential difference will be generated on the crystal due to its property. The voltage produced will be proportional to the magnitude of the applied force.
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  Advantages of Piezoelectric Transducers •High frequency response: They offer very high frequency response that means the parameter changing at very high speeds can be sensed easily. • High transient response: The piezoelectric transducers can detect the events of microseconds and also give the linear output. • The piezoelectric transducers are small in size and have rugged construction.
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  Limitations of Piezoelectric Transducers •Low Output: The output obtained from the piezoelectric transducers is low, so external electronic circuit has to be connected. • High impedance: The piezoelectric crystals have high impedance so they have to be connected to the amplifier and the auxiliary circuit, which have the potential to cause errors in measurement. To reduce these errors amplifiers high input impedance and long cables should be used. • Forming into shape: It is very difficult to give the desired shape to the crystals with sufficient strength.
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  Applications of thePiezoelectric 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
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  • 3)Used alongwith 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)Used in medical treatment, sonochemistry and industrial processing equipments for monitoring the power. • 6)Used in Inkjet printers • 7)Used in smartphone screens. • 8)Used in lighters.
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