Transcript Activity: A Peizoelectric Smart Sensor

Activity: A
Peizoelectric Smart
Sensor
PVDF-A polymer with many uses
What is a Smart Sensor?
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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.
Preparation for Activity
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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
Discussion Points

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What is the piezoelectric effect?
Why is the b form of PVDF piezoelectric?
How is the b form of PVDF produced?
Design Problems
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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
Representations of the molecular structure of the
vinylidene difluoride (VD) monomer and of the a
and b forms of the PVDF polymer.
F
H
F
H
VD-wire
PVDF-b form
PVDF-a form
VD-space filling
Commercially available metal coated
piezoelectric PVDF sensor elements
Electronic Circuits
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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
(B) Electric
Charge
Measurement
(C) Differential
Amplifier, for
measuring
relative/combined
signals
Deflection Sensor
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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
Output PVDF sensors on flexed rulerNote polarity (green/yellow). Blue
represents output of circuit (C).
Output PVDF sensors on flexed ruler
damped motion-Note polarity
(green/yellow) and combined signal.
Plot of ln(Displacement) vs time showing that the motion of
the solid material is described by the equation D=D0 exp (t/t); this is the equation for an under damped oscillator.
6
5
Ln(D)
4
3
LnI
Linear (LnI)
2
1
0
0
50
100
Time
150
200
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.
USB data port interfaced to laptop
computer gives system properties of
a “smart sensor”.
Discussion Points II

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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?