User Manual

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Figure 1. Typical infrared absorption spectrum of PVDF film.
INTRODUCTION
Transducer materials convert one form of energy into another, and are widely used in sensing
applications. The tremendous growth in the use of microprocessors has propelled the demand for
sensors in diverse applications. Today, PIEZOELECTRIC POLYMER SENSORS are among
the fastest growing of the technologies within the $18 billion worldwide sensor market. Like any
new technology, there have been an extraordinary number of applications where "PIEZO FILM"
has been considered for the sensor solution. In the 20 years since the discovery of piezoelectric
polymer, the technology has matured, practical applications have emerged from a long list of
possibilities, and the rate of commercialization of the technology is accelerating.
These documents provide an overview of piezoelectric polymer technology and nomenclature, its
properties, and sensor design considerations. It also explores a range of sensor applications that have
been successfully developed in recent years.
Solving unique sensor problems is a particular strength of our group of applications engineers. We
welcome the opportunity to provide assistance to you during your evaluation of piezo film sensors
for your design.
BACKGROUND
Piezoelectricity, Greek for "pressure" electricity, was discovered by the Curie brothers more than
100 years ago. They found that quartz changed its dimensions when subjected to an electrical field,
and conversely, generated electrical charge when mechanically deformed. One of the first practical
applications of the technology was made in the 1920's by another Frenchman, Langevin, who
developed a quartz transmitter and receiver for underwater sound - the first SONAR. Before World
War II, researchers discovered that certain ceramic materials could be made piezoelectric when
subjected to a high polarizing voltage, a process analogous to magnetizing a ferrous material.
By the 1960's, researchers had discovered a weak piezoelectric effect in whale bone and tendon. This
began an intense search for other organic materials that might exhibit piezoelectricity. In 1969,
Kawai found very high piezo-activity in the polarized fluoropolymer, polyvinylidene fluoride
(PVDF). While other materials, like nylon and PVC exhibit the effect, none are as highly
piezoelectric as PVDF and its copolymers.
Like some other ferroelectric
materials, PVDF is also
pyroelectric, producing
electrical charge in response to
a change in temperature.
PVDF strongly absorbs
infrared energy in the 7-20µm
wavelengths (see Figure 1),
covering the same wavelength
spectrum as heat from the
human body. Accordingly,
PVDF makes a useful human
motion sensor as well as
pyroelectric sensor for more
sophisticated applications like
vidicon cameras for night
vision and laser beam profiling sensors. A dense infrared array has been recently introduced that
identifies one’s fingerprint pattern using the pyro effect of piezo polymer.