Activity: A Peizoelectric Smart Sensor

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Activity A Peizoelectric Smart Sensor

• PVDF-A polymer with many uses

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What is a Smart Sensor?

• We will use the term Smart Sensor to refer to
  systems that employs a sensor device mated to
  microelectronics. In this activity we will use
  metal coated PVDF films as our sensor system and
  a computer will take the place of the
  microelectronics. The system used in this
  activity is not engineered to minimize size and
  power consumption but clearly those would be
  goals in any widely deployed commercial device.

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Preparation for Activity

• Items Needed PVDF sensor films electronic
  components for circuits A and C (to be described)
  computer with data acquisition
  hardware/software.
• An understanding of piezoelectric effect
• An understanding of the role of molecular
  structure in determining the peizoelectric
  properties of PVDF 

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Discussion Points

• What is the piezoelectric effect?
• Why is the b form of PVDF piezoelectric?
• How is the b form of PVDF produced?

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Design Problems

• Design a PVDF based smart sensor system to give
  point in time information on the number of open
  spaces in a parking garage
• Design a sensor system to measure the velocity
  of a falling ball
• Design a sensor system to measure the vibrations
  in a factory building

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Representations of the molecular structure of the
vinylidene difluoride (VD) monomer and of the a
and b forms of the PVDF polymer.
                
VD-wire
PVDF-a form
PVDF-b form
VD-space filling
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Commercially available metal coated piezoelectric
PVDF sensor elements
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Electronic Circuits

• PVDF generates a measureable voltage
• Circuits with a very high Input impedance
  required
• Low power consumption, battery operated systems
  desirable for portability.

(A) Impedance Adaptor, Voltage Follower
(C) Differential Amplifier, for measuring
relative/combined signals
(B) Electric Charge Measurement
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Deflection Sensor

• Two PVDF sensors- the sensors are mounted on both
  sides of a flexible material.
• The response of these films capable of
  quantifying the magnitude, speed and direction
  of the flexion movement.
• Circuit (A) used to follow voltage changes
• Circuit (C) is used to obtain a composite signal
  from the two sensors

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Output PVDF sensors on flexed ruler-Note polarity
(green/yellow). Blue represents output of circuit
(C).
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Output PVDF sensors on flexed ruler damped
motion-Note polarity (green/yellow) and combined
signal.
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Plot of ln(Displacement) vs time showing that the
motion of the solid material is described by
the equation DD0 exp (-t/t) this is the
equation for an under damped oscillator.
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PVDF sensors mounted on a solid substrate and
connected to circuit (A). Circuit (A) output is
directed to a USB data acquisition system
interfaced to a laptop.
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USB data port interfaced to laptop computer gives
system properties of a smart sensor.
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Discussion Points II

• How can we distinguish the piezoelectric and
  pyroelectric responses exhibited by a PVDF film?
• What is needed in terms of electronics to produce
  a peizoelectric PVDF smart sensor?
• Suggest new applications of PVDF piezoelectric
  sensors?