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Basic principles
• The effect is explained by the displacement of ions in crystals that have a nonsymmetrical
unit cell
• When the crystal is compressed, the ions in each unit cell are displaced, causing the electric
polarization of the unit cell.
• Because of the regularity of crystalline structure, these effects accumulate, causing the
appearance of an electric potential difference between certain faces of the crystal.
• When an external electric field is applied to the crystal, the ions in each unit cell are
displaced by electrostatic forces, resulting in the mechanical deformation of the whole crystal.
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Basic equations I
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Basic equations II
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Problem
Problem:
Calculate the voltage generated across a PZT piezo chip acting as pressure sensor diaphragm, if d11 = 289
pC/N, and is subjected to a pressure of 100 KPa. Assume the thickness of the PZT diaphragm is 50 µm.
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Piezoelectric materials
Polymers
F
H
F
H
• PVDF is piezoelectric and the voltage induced by
bending PVDF films can be measured. The surface
of the PVDF is coated with metal to allow electrical
measurements.
• PVDF is pyroelectric and readily absorbs thermal
radiation in the range 1000-1200 cm-1. The voltage
induced by exposing metalized PVDF films to
thermal radiation can be measured.
• By virtue of its piezoelectric properties PVDF
possibly could be fabricated into a surface acoustic
wave based sensing system.
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Piezoelectric materials
Polymers
Piezo film is a flexible, lightweight, tough engineering plastic available in a wide
variety of thicknesses and large areas. Its properties as a transducer include:
• Wide frequency range—0.001 Hz to 109 Hz.
• Vast dynamic range (10-8 to 106 psi or μ torr to Mbar).
• Low acoustic impedance—close match to water, human tissue and adhesive systems.
• High elastic compliance
• High voltage output—10 times higher than piezo ceramics for the same force input.
• High dielectric strength—withstanding strong fields (75V/μm) where most piezo ceramics
depolarize.
• High mechanical strength and impact resistance (109—1010 Pascal modulus).
• High stability—resisting moisture (<0.02% moisture absorption), most chemicals, oxidants,
and intense ultraviolet and nuclear radiation.
• Can be fabricated into unusual designs.
• Can be glued with commercial adhesives.
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