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Eelectric
Energy Harvesting
Through Piezoelectric Polymers
Final Report – May 13
Don Jenket, II
Kathy Li
Peter Stone
Presentation Overview
Objective
Background
Materials Choice & PVDF Properties
Electrical Properties
Strain-Voltage Relationships
Circuitry
Conclusions
Future Suggestions
Acknowledgements
May 13, 2004
Eelectric
Final Report
Background
DARPA Objective: Convert
mechanical energy from a fluid
medium into electrical energy


Fluid flow creates oscillations in an
eel body
Creates strain energy that is
converted to AC electrical output
by piezoelectric polymers
http://www.darpa.mil/dso/trans/energy/pa_opt.html
3.082 Objective: Demonstrate that piezoelectric
materials can be used to harness power from
airflow and determine the maximum amount of
useful power that can be harvested with a single
eel tail
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Eelectric
Final Report
Materials Selection
http://web.media.mit.edu/~testarne/TR328/node7.html
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Eelectric
Final Report
Poly(vinylidene fluoride)
PVDF
F
H
Properties
Chemically
Inert
Flexible
High
C
C
F
H
n
Mechanical Strength
Production
React
HF and
methylchloroform in a refrigerant gas
Polymerization from emulsion or suspension by free
radical vinyl polymerization
References: http://www.psrc.usm.edu/macrog/pvdf.htm, Accessed on: 3-9-04; Piezoelectric SOLEF PVDF Films. K-Tech Corp., 1993.
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Eelectric
Final Report
Piezoelectric PVDF
Molecular Origin


Fluorine atoms draw electronic density away from carbon
and towards themselves
Leads to strong dipoles in C-F bonds
Piezoelectric Model of PVDF (Davis 1978)


Piezoelectric activity based upon dipole orientation within
crystalline phase of polymer
Need a polar crystal form for permanent polarization
b-phase
(piezoelectric)
a-phase (antiparallel dipoles)
Davis, G.T., Mckinney, J.E., Broadhurst, M.G., Roth, S.C. Electric-filed-induced phase changes in poly(vinylidene fluoride). Journal of Applied Physics 49(10), Oct, 1978.
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Poling - Bauer Process
Biaxially stretch film: Orients some crystallites with their
polar axis normal to the film
Application of a strong electric field across the thickness
of the film coordinates polarity
Produces high volume fractions of b-phase crystallites
uniformly throughout the poled material
Selected Properties of 40 mm thick bioriented PVDF
Electromechanic coupling factor
0.11
Young’s Modulus
~2,500 MPa
Melting Point
175º C
Depoling Temperature
90º C
Table courtesy of K-Tech Corporation
Reference: Piezoelectric SOLEF PVDF Films. K-Tech Corp., 1993.
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Eelectric
Final Report
Design Schematic
Tail
Kapton
Holder Tape
PVDF
Flagpole
Fan
0.005”
Magnet
Wire
Silver Paste
Electrode
Tail
Weight
Electrical
Output
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Final Report
Strain in a Cantilever
y
x 
R
y is the distance from the neutral plane and R is the Radius of
Curvature:
Strain in a bending cantilever goes as:
3
L
R
3( L  l )z
at a distance l from the fixed end and the free end deflection
is dz for a cantilever of total length, L. Thus for a cantilever of
thickness, H
3H
x (l ) 
( L  l )z
3
4L
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Final Report
Strain-Induced Voltage
In 31 piezoelectric coupling:
E3  h31x1 (l )
The charge induced due to the strain at point l:
Qdl   3E31(l ) w  dl
L
Qtot 
and
Q
dl
dl
0
So the voltage induced across the surface is:
L
QTot
V 

C
 3  h31  w   x1 (l )dl
0
C
This is simply the length-averaged voltage, leading
to:
2
QTot 3  H 
V
   h31z
C
8 L 
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Final Report
Strain-Induced Voltage
Displacement
(cm)
0.0
Radius of
Curvature at
Midpoint (m)
Inf
Normal
Strain
(*10-5)
0
0.5
1.0
1.5
2.0
2.5
3.0
19.8
1.92
0.96
0.64
0.48
0.384
0.32
0.048
0.521
1.04
1.56
2.08
2.60
3.13
20.7
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Voltage Expected
(mV)
Voltage*
(mV)
~20
0
64
80
106
163
202
232
55.4
110.81
166.21
221.61
277.02
332.42
2200
Final Report
Strain-Induced Voltage
Voltage vs. Strain
350
Voltage (mV)
300
250
y = 7E+06x + 17.25
R2 = 0.9837
200
150
100
50
0
0.00E+00 5.00E-06 1.00E-05 1.50E-05 2.00E-05 2.50E-05 3.00E-05 3.50E-05
Average Normal Strain (unitless)
Experimental
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Theoretical
Eelectric
Linear (Experimental)
Final Report
Oscillation Frequency
Fan Off
Fan On
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Final Report
Tail Capacitance
C =  A/d



A = 7.5 * 10-4 m2
 (at < 0.1 kHz) = 11.5o ±10%
d = 4 *10-5 m
Calculated Capacitance



Lower bound: 1719 pF
Upper bound: 2099 pF
Median: 1910 pF
Actual Capacitance at 10-100 Hz: 1940 pF
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Oscilloscope Data
2cm x 12cm Piezoelectric PVDF in Wind
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Tail Power Output
Resistance
(W)
Power =
V2/R (nW)
10 000
Peak
Voltage
Amplitude
(mV)
35.1
100 000
91.7
84
1 000 000
301
91
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Final Report
Tail Current Output
Resistance (W) Voltage (mV) Current (mA)
10 000
35.1
3.51
100 000
91.7
0.917
1 000 000
301
0.301
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Final Report
Rectifier Circuit
Diodes
LED
AC
Capacitors
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Final Report
Increasing Voltage
Series Connection of Two Tails
600
Voltage (mV)
400
200
0
0
2000
-200
-400
2 Tails
1 Tail
-600
Time (ms)
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Series Connection
of 2 Tails
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Final Report
Series Connection
of 3 Tails
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Conclusions
PVDF tails can successfully harness energy from air
to useful electric output
The electrical properties of 2 x 12 cm tails have been
characterized


Frequency and Capacitance
Power and Current
A relationship has been quantified between strain and
voltage in this design


Linear relationship
Compares well with cantilever model
A series connection of two tails in phase has been
established to increase voltage


One tail: ~300 mV amplitude
Two tails: ~500 mV amplitude
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Final Report
Future Work
Troubleshoot connections


Successfully connect more than two tails in series
to get useful voltages
Exploit parallel connections to increase current
Better piezoelectric materials

Active Fiber Composites



PZT fibers in an epoxy matrix
Combine flexibility and good electromechanical
coupling
Currently, they are too stiff to be oscillated by
natural forces
May 13, 2004
Eelectric
Final Report
Acknowledgements
Professor Yet-Ming Chiang
Professor David Roylance
Joe Parse & Yin-Lin Xie
Joe Adario & David Bono
May 13, 2004
Eelectric
Final Report