Piezoelectric Film Transducers
"Imagination is more important than knowledge."
Table of Contents
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Executive summaryTransducers convert one form of energy into another. They have a range of uses, particularly as sensors. In the last 20 years Polyvinylidene Fluoride, or (PVDF), Film along with the piezo electric effect has been used in thousands of sensing applications. These applications range from infrared sensors, stress gauges, and vibration detectors. There is still a myriad of possibilities to which PVDF Film can be applied. The purpose of this lab is to familiarize you with PVDF Film, and to give you an idea of its possibilities.
After completing this lab a student should be able to:
1. Understand the basic properties of PVDF Film.
2. Familiarize themselves with some applications of the film.
3. Integrate LabVIEW by controlling the DMM and Power Supply.
Background InformationThe piezoelectric effect was discovered in the late 1800s by the Curie brothers. It was discovered that when certain ceramic and crystalline structure underwent some kind of deformation they emitted an electrical pulse. Conversely, when an electrical current was run through the material it would vibrate. The first application of this technology was for SONAR. In 1969 PVDF was first created. It was found that the piezoelectric effect was higher than that found in materials used previously.
Figure 1 - Simple piezo film sensors.
Figure 2 - A piezo buzzer, commonly used in every day products because of its size, weight and durability. It is also inexpensive and requires little power, which makes it an ideal electrical device.
ProceduresPart A - Basic Piezo Film Qualities
Figure 3 - Schematic for set-up of Part A.
|Warning - Use common sense, hotplates get hot! Don't let the piezo film touch the hotplate or the film will melt and be destroyed|
Also, make sure to turn off the hotplate when you are finished!
Figure 4 - Schematic for set-up of Part B.
1. Turn the DC Power Supply on and set Output 1 to a voltage in the range of the specification on the buzzer. Disable the output. Now connect the buzzer to Output 1, making sure that the positive alligator clip is attached to the lead on the buzzer marked as positive. Turn the Output 1 on, and listen to the sound created. Try using a different voltage, does it affect the sound?
Figure 5 - Schematic for set-up of Part C1.
2. Turn off the Power Supply, and connect the piezo buzzer to the function generator as shown in Figure 6. Set it to the same voltage used in step one. Now set the frequency to 1.7 KHz. Try panning the frequency up to 11.8 KHz. Notice the change in pitch and volume.
Figure 6 - Schematic for set-up of Part C2.
3. In this step, the same qualities will be examined, but in reverse. Instead of the piezo film being used as a speaker, you will use it as a microphone. To do this, a styrofoam cup will aid us in the absorbtion of the sound waves, which will then be picked up by the second piezo sensor, and finally converted into electrical form.
First, tape the piezo sensor to the back of a stryofoam cup. Then connect the leads of the sensor to the oscilloscope, as was done previously in figure 3. Now you should have a working microphone. Try speaking into the cup, and notice the voltage on the oscilloscope. The frequency of the output corresponds to the pitch of your voice.
Figure 7 - Front panel view of piezo virtual instrument.
Figure 8 - Setup of Part D.
1. What does PVDF stand for?.
2. Explain the piezoelectric effect and list 3 conditions that cause piezo film to produce electricity.
3. List five applications of piezo film.
4. When a force is applied to a piece of piezo film causing it to flex, why does the voltage stop quickly even when the force is still present?
5. Based on what you saw with the oscilloscope, sketch the voltage as a function of time of what you would expect the output to be if a piece of piezo film is placed in the path of a rotating fan blade.
6. Explain the importance of the material in engineering.
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