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 makes it an excellent sensor for infrared (heat) detection of the human body. Film sensors are commonly employed in motion sensors, where with the use of a fresnel lens, can detect a human body at fifty feet.
Experimenting with this piezoelectric material is fun. We will make a microphone, acoustical instrument pick-up, CMOS switch, speakers, and look at its use as vibration sensors and piezo-actuator. Before we build any of these demonstration sensors let's look a little closerat some of its properties.
Piezo film has an extremely high output voltage, about 10 times greater than ceramic materials. Since the material is a thin light weight flexible film it can be glued onto shaped designs (One ca use a variety of commercial glues). The material has a high mechanical strength and is impact resistant.
Other attributes include:
- 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 piezo electric ceramics.