By John Iovine
The word piezo is derived from the
Greek word piezein, meaning to press
tight or squeeze. Add the second term
electric and you’ve got squeezed
Piezoelectric materials develop a
momentary electric potential (voltage)
when the material is placed under a
mechanical strain. Inversely,
piezoelectric materials will strain
internally or change shape dimensionally
(slightly) when placed under a suitable
electrical field. (See Figure 1.)
■ Completed circuit board connected to audio
source and piezoelectric film speaker.
Naturally occurring piezoelectric materials are crystals. The piezoelectric effect was discovered by Pierre and
Jacques Curie. In 1880, the Curie brothers published a
paper on the piezoelectric phenomena and
crystallographic structure of tourmaline, quartz, topaz,
cane sugar, and Rochelle salt.
Since piezoelectric materials only develop momentary
electrical potentials, in order for the electric potential
generated to power an electrical device, the mechanical
strain must oscillate to provide continual power to the
Figure 2 illustrates what the electrical response of a
finger tap on piezoelectric film would look like on an
oscilloscope. The initial pulse rapidly decays while
In this article, we will experiment with a unique
piezoelectric material: piezoelectric film. Piezoelectric film
is made from polyvinylidene fluoride (PVDF) which is a
non-reactive thermoplastic. The piezoelectric effect in
PVDF material was first observed in 1969 by Kawai.
To make PVDF piezoelectric, the material must become
anisotropic meaning the molecular structure of the plastic
compound must be aligned to create a piezoelectric effect.
This is achieved using two processes during
manufacturing. The heated PVDF material is extruded and
stretched in the length direction into paper thin material.
This stretching causes some alignment of the internal
plastic dipoles. To enhance the alignment of the dipoles, a
high voltage “poling” voltage is applied to the
surfaces of the plastic sheet material. This
aligns most of the dipoles in the thickness
direction that is perpendicular to the surfaces
(see Figure 3).
The surfaces of the stretched and poled
PVDF sheet material is then metalized with
thin, electrically conductive nickel copper
■ FIGURE 1. Electrical response of
piezoelectric film to pressure.