Download Activity: A Pyroelectric Smart Sensor

Activity: A
Pyroelectric 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.
Am understanding of Piezoelectric Effect
An understanding of Pyroelectric Effect
An understanding of the role of molecular
structure in determining the piezoelectric
properties of PVDF
Discussion Points
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Why is the b form of PVDF piezoelectric?
How is the b form of PVDF Produced?
What is the relationship between
piezoelectric effect and the pyroelectric
effect?
What does the infrared spectrum of PVDF
tell us about the wavelengths where the
pyroelectric properties of PVDF might be
most easily observed?
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
Infrared Spectrum of PVDF taken on a Bruker IFS 66v spectrometer,
equipped with a DTGS detector and a KBr beamsplitter.
Note that the strong absorption around 1000 cm-1
Discussion Points II
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How can we detect the piezoelectric or
pyroelectric effect exhibited by a PVDF film?
What is needed in terms of electronic and
computer components to produce a smart
sensor?
Commercially available metal coated
piezoelectric PVDF sensor elements
A Film
in (mm)
B Electrode
in (mm)
C Film
in (mm)
D Electrode
in (mm)
t (µm)
Cap (nF)
.520 (13)
.400 (10)
.980 (25)
.580 (14.70)
205
.500
.640 (16)
.484 (12)
1.63 (41)
1.19 (30.17)
205
1.38
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
Four Panel Thermal DetectionIndividual panels are connected to a
dedicated circuit (A).
USB data port interfaced to laptop
computer gives system properties of
a “smart sensor”.
Voltage output 4 panel Pyroelectric Sensor when
exposed to an asymmetrically located heat source
Discussion Points
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Design a pyroelectic smart sensor system
capable of to locating a single person in a room.
Design a system which would make a PVDF
pyroelectric sensor sensitive to a wide range of
wavelengths.
What information might be obtained from the
voltage rise and decay exhibited on the thermal
response curves
What can be done to stabilize a PVDF
pyroelectric sensor system?