Transcript Final Presentation

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
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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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Materials Selection
http://web.media.mit.edu/~testarne/TR328/node7.html
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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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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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Design Schematic
Tail
Kapton
Holder Tape
PVDF
Flagpole
Fan
0.005”
Magnet
Wire
Silver Paste
Electrode
Tail
Weight
Electrical
Output
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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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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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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
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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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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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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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Rectifier Circuit
Diodes
LED
AC
Capacitors
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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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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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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
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Acknowledgements
Professor Yet-Ming Chiang
Professor David Roylance
Joe Parse & Yin-Lin Xie
Joe Adario & David Bono
May 13, 2004
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Final Report