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Polyvinylidene Fluoride. A polymer that becomes piezoelectric when congealed under a strong electric field .

The piezoelectric properties of PVDF were discovered in the 1970's. Before that, only ceramic and crystal piezoelectrics were used, such as PZT and quartz. Because PVDF is very flexible due to it's polymer structure, it can be used in much more shapes and sizes than the brittle PZT.

Some caracteristics:

d31 Piezoelectric charge constant   23 · 10-12 C/N
g31 Piezoelectric voltage constant 216 · 10-3 Vm/N
k31 Coupling factor               0.12
Y   Young's modulus             2 to 4 · 10-9 N/m²
ε   Permittivity                   110 · 10-12 F/m

Structural formula:

  F   F   F   F
  |   |   |   |
  C   C   C   C
 / \ / \ / \ / \ /
    C   C   C   C
    |   |   |   |
    H   H   H   H

Typical applications: hydrophones, speakers, pressure sensors.

Source of numbers: Measurement Specialties, Inc http://www.msiusa.com/piezo_documentation.htm