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■ FIGURE 2. Electrical response
of piezoelectric film shown on
an oscilloscope.
alloy on both sides to provide
electrical contact.
To use piezo film, one
makes an electrical connection
to the electrically conductive
coating on each side of the
PVDF material. If one needs to
attach electrical connections to
raw piezo film, this is
accomplished using either
copper tape or a conductive
epoxy. Soldering directly to the
film is not possible because
the heat would destroy the
underlying plastic PVDF material. The piezo film speaker
has a two-pin .100” header connection that we can easily
use to connect to our circuit.
mechanical strength and is impact
resistant. Other attributes include:
■ FIGURE 3 Dipole
molecules in random
arrangement and
aligned arrangement
after stretching and
poling voltage.
Pyroelectric
PVDF is also pyroelectric, meaning that it produces an
electrical charge in response to a change in temperature.
The material is sensitive to infrared energy between 7-20
um. This response allows it to be used for heat detection
of the human body. Piezoelectric film sensors are used
behind the fresnel lens in motion sensors where they can
detect a human body at 50 feet.
• Wide frequency range (.001 Hz - 10^ 9 Hz).
• Low acoustical impedance (close to water and human
tissue; efficient for sonar and imaging).
• High dielectric strength.
• Good mechanical strength.
• Moisture resistant, inert to many chemicals.
One disadvantage to piezo film is that it is a weak
electromechanical transmitter when compared to
piezoelectric ceramics.
Ultrasonic Transducer
Piezoelectric Film Speaker
Piezoelectric film was used as an ultrasonic transducer
for range finding in a few old Polaroid sonar cameras like
the One-Step and SX- 70. The sensor performed a dual
function of first sending out an ultrasonic burst, and then
acted as a receiver to catch the reflecting echo. The time
lapse between the transmission and receiving the echo
provided the range to the subject for the camera to focus.
These sensors, as well as supporting electronics, are still
available from Senscomp.
Piezoelectric
Film Properties
Piezoelectric film has
an extremely high output
voltage, about 10 times
greater than piezoelectric
ceramic materials. Since the
material is a thin, lightweight
flexible film, it can be
glued on to shaped designs
(one may use a variety of
commercial glues). The
material has a high
PARTS LIST
• Piezoelectric Film Speaker
• Printed Circuit Board
• Eight-pin DIP Socket
• LM386 Audio AMP IC
• Slide Switch
• 9V Battery Terminals
• 10K Potentiometer PC Mount
• 390 ohm 1/4 watt Resistor
• 1.2K ohm 1/4 watt Resistor
• 10 ohm 1/2 watt Resistor
• ( 2) 10 µF Capacitors
• .047 µF Capacitor
• 250 µF Capacitor
• ( 2) Two-pin female sockets
• Mini Step-up Transformer
When an electric field is applied to a piezoelectric
film, it deforms (see Figure 4). The film is able to
compress and expand across its thickness under the
influence of an electric field. It is this property that allows
it to perform as a flat film speaker. For efficiency, a large
piece of piezo material is used. The piezoelectric film
■ FIGURE 4. Audio signal impact on piezoelectric
film speaker.
November 2010 35
