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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.

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Basic principles

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  1. 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. Basic principles

  2. Basic equations I 2

  3. Basic equations II 3

  4. 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. Problem

  5. Piezoelectric materials Polymers • 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. 5

  6. 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. 6

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