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Pyroelectric conversion: Harvesting Energy from
Temperature Fluctuations
Dr. Àngel Cuadras
Instrumentation, Sensors and Interfaces GroupCastelldefels School of Technology
Universitat Politècnica de Catalunya (UPC)
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COLLABORATIONS
• University of Brescia. (Dept. Electronics for Automation and INFM)– A. Ghisla, V. Ferrari, M. Ferrari
• Instrumentation, Sensors and Interfaces GroupCastelldefels School of Technology– Dr. Gasulla, Dr. Pallàs
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INTRODUCTIONThermal energy
•Present everywhere
•Thermodynamical restrictions
Sun
Fire
Thermal to electrical conversion– Thermoelectricity: thermal gradients– Pyroelectricity: from thermal time-dependent fluctuations
Industry Hot PipesEngines
Sources
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OUTLINE
• History• Pyroelectric Effect• Materials• Applications: Sensors and Harvesters• Experimental harvesters• Conclusions
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HISTORY
• Phenomenon observation– Classic Greeks: Theophrastus (314 BC)– XVIIIth and XIXth: phenomenon observation
• Description and quantification– Classical explanation: Lord Kelvin– Quantical explanation: Born
• Researchers: – Schrödinger, Röntgen and P. Curie, among others
• Applications:– Sensors: Yeou Ta…– Harvesters investigated by Olsen et al., Ikura…
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PHYSICAL DESCRIPTION
• Crystalline structures
∆
Cubic structure
Cations (Pb,Ti,Ca,Ta…)
Anions (O)
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PHYSICAL DESCRIPTION
• Crystalline structures• Point symmetry
Tetragonal structure
Cations (Pb,Ti,Ca,Ta…)
Anions (O)
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PHYSICAL DESCRIPTION
Structure Deformation ∆
•Mechanical stress
•Thermal stress
•Electrical stress
• Crystalline structures• Point symmetry
Tetragonal structure
Piezoelectric
Pyroelectric
Ferroelectric
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PHYSICAL DESCRIPTION
Structure Deformation ∆
•Mechanical stress
•Thermal stress
•Electrical stress
• Crystalline structures• Point symmetry
Tetragonal structure
Pyroelectric
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PHYSICAL DESCRIPTION
• Crystalline structures• Point symmetry
Structure Deformation ∆
•Mechanical stress
•Thermal stress
•Electrical stress
Tetragonal structure
+++++++++++++++++++++
- - - - - - - - - - - - - - - - - - - -Pyroelectric
∆ ∆T∆V
Ion displacement due to ∆T Induced charge
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PHYSICAL DESCRIPTION
Structure Deformation ∆
•Mechanical stress
•Thermal stress
•Electrical stress
• Crystalline structures• Point symmetry
ParaelectricT>TC
Ion symmetry no induced chargeCubic structure
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PYROELECTRIC EFFECT
300 305 310 3150
50
100
150
200
250
p
T (K)
p (1
0-4 C
m-2 K
-1)
-25
-20
-15
-10
-5
0
TCurie
P(µ
C m
-2)
P
s ss
dQ dP dTI Spdt dt dt
= = =
ss
dPpdT
=
•Temperature increase•Polarization
•Dependence of p on T
•Maximum temperature Curie temperature, phase transition
•Induced current as a function of T
TGS
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PYROELECTRIC MATERIALS
LiTaO3
• Crystal materials – CaTiO3,LiTaO3,PbTiO3– Triglycine sulfate (TGS)– Growth methods: Czochralki, water dissolution
• Ceramics – PZT - Lead zirconate titanate – Growth methods: Screen printing– Poling
• Polymers – PVDF-Polyvinylidene Difluoride– Growth methods: Chemical processing
TGS
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MATERIALS DESCRIPTION• Pyroelectric coefficient (p)
– Thermal energy conversion to electrical conversion • Thermal capacitance (cV)
– Thermal energy stored in the lattice• Electrical permittivity (ε= ε0εr)
– Electrical energy stored in the lattice• Figure of Merit
0V r
pFoMc ε ε
=
Material p(10-4 C m-2 K-1)
εr(1 kHz)
TC(ºC)
cv(J cm-3 K-1)
TGS 3.5 35 49 2.5LiTaO3 2.3 46 665 3.2
PZT 1.6 1350 320
PVDF 0.3 12 80 2.4
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OUTLINE
• History• Pyroelectric Effect• Materials• Applications: Sensors and
Harvesters• Experimental harvesters• Conclusions
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APLICATIONS: SENSORS
• Proposed by Yeou Ta in 1938
• Application: IR sensors, burglar alarms
• Advantages– Wide thermal and electromagnetic
sensitivity– Fast response (0 to 10 Hz) – Low-cost– Good signal to noise ratio– Work at ambient temperature
• Scientific and commercial development
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APPLICATIONS: HARVESTERS
R. B. Olsen, D. A. Bruno, and J. M. Briscoe,
"Pyroelectric Conversion Cycles," J. Appl. Phys. 58 (1985) 4709
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PYROELECTRICITY: YES OR NOT?
YES?
• Low cost• Infinite thermal sources
NOT?
• Low power generation• Low conversion efficiency• Temperature fluctuations
Estimation:
S = 10 cm2
λ= 10-4 C m-2K-1 ⇒
dT/dt= 10 K s-1
I = 1 µA
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MODELING CONVERSION
W RTCT
T VI ReCe
Thermal model Electrical model
· ·dTI S pdt
=
e
· ·S p TVC
∆∆ =
Harvester critical parameters
RT and CT : thermal conductivity and thermal capacitance
Re and Ce : electrical losses and electrical capacitance
Efficiency (< 1 %)
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OUTLINE
• History• Pyroelectric Effect• Materials• Applications: Sensors and Harvesters• Experimental harvesters• Conclusions
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EXPERIMENTAL SETUP
Heating– 298 K to 370 K– Warm air – Halogen lamp
Current Measurement
Voltage measurementElectrometer Keithley 616
Resistance measurementElectrometer Keithley 616
R up to 1014 Ω
RfI
VO AcquisitionSystem Agilent
Thermal measurement•SMD Thermistor
•Fast thermal response
•Sensitivity up to 0.01 K
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PZT STUDIED HARVESTERS
Alumina Substrate
Bottom electrode PdAg (contact)
PZT Technology
•Ceramic powder
•Screen printing.
•Firing
•Poling
Sample ID Target Thickness (µm)
Poling Field (MV/m)
1 60 5
2 60 7
3 100 5
4 100 7
4 cm
4 cm
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PZT FORMATION
Tpoling
+-
Random orientation of
dipoles
Remanent polarizationDC field application:
poling
Dipole orientation
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PZT CONVERTERS
0 50 100 150 200 250 300
-0,1
0,0
0,1
0,2
0,3
I
I (µA
)
Time (s)
300
310
320
330
340
350
T
T(K)
-0,5
0,0
0,5
1,0 dT/dt
dT/dt (K/s)
Air Heating:
• Step function
• Large thermal inertia
Pyrocurrent follows dT/dt
Imax = 0.3 mA
Generated charge density
Q = 0.75 C·cm-2
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PZT CONVERTERS
Air Heating:
• Step function
• Large thermal inertia
Pyrocurrent follows dT/dt
Imax = 0.3 mA
Generated charge density
Q = 0.75 C·cm-2
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PZT CONVERTERS
Technological dependence:
• Poling Field
• Thickness
0 20 40 60 80 100
-0.1
0.0
0.1
0.2
0.3 Constant poling field5 MV/m
1 3
I (µA
)
Time (s)
Optimized design
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PVDF CONVERTERS
Measurement Specialties Inc.
Piezoelectrical Film
PVDF large area technology
Sample ID
Thickness (µm)
Area(cm-2)
C (nF)
A1 70 3.6 0.740
A2 40 7.44 2.78
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PVDF CONVERTERS
0 10 20 30 40 50 60-0.4
-0.2
0.0
0.2
0.4
3.60 cm-2
7.44 cm-2
I (µA
)
Time (s)
• Warm air flow/fan
• Temperature fluctuation
(298 K 335 K)
• Peak current
• Generated Charge density
Q = 0.24 C·cm-2
• Symmetry in heating and cooling
0 1 0 2 0 3 0
0
1
2
3
4
dT/
dt (K
/s)
T im e ( s )
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IMPROVING HARVESTERS
• Cell association• Energy storage• Thermal cycling
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PARALLEL ASSOCIATION
0 25 50 75 1000,0
0,1
0,2
0,3
0,4 3 4 3||4
I (µA
)
time (s)
Parallel Cell Association
Current addition
Stacked structures
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ENERGY STORAGE
•Low power systems strategy
•Rectification + storage
•Impedance matching overcome
•Energy loss at diodes
•Capacitor charge
Ce
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THERMAL CYCLING
0 100 200 300 400 5000
1
2
3
4
5
6
V (V)
Time (s)V(
V)
300
310
320
330
340
Tem
pera
ture
(K)
T (K)
PZT PVDF
0 50 100 150 200 250 300 3500
2
4
6
8
10
12
V
V (V
)
time (s)
300
310
320
330
340
Tem
pera
ture
(K)
T
( ) · ·1 12 2
N N
S L e L eo
e L e e L e
Q C C C CS p TV NC C C C C C
⎡ ⎤ ⎡ ⎤⎛ ⎞ ⎛ ⎞− −∆⎢ ⎥ ⎢ ⎥= − = −⎜ ⎟ ⎜ ⎟+ +⎢ ⎥ ⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎣ ⎦( ),max
· ·2o
e
S p TV NC∆
→ ∞ =
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BEYOND PYROELECTRICITY
0 100 200 300 400-0,3
-0,2
-0,1
0,0
0,1
0,2
0,3
I
I (µA)
Time (s)
300
320
340
360
Tem
pera
ture
(K)
T •Materials sensitive to external influences.
•Generated current from a PZT when illuminated.
•Current is not proportional to dT/dt.
•Combination of different effects in a single harvester
•Piezoelectrical response – when undergo mechanical stresses
•Semiconductor – heated with light
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CONCLUSIONS
• Pyroelectricity has been revisited• PZT and PVDF cells have been developed and
modeled.• Parallel association increases the current.• Energy can be effectively transferred and stored in
capacitors.• Further research in order to effectively power low power
systems.
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QUESTIONS?
Castelldefels School of Technology (EPSC),Universitat Politècnica de Catalunya (UPC)
Av. Canal Olimpic s/n08860 Castelldefels (Barcelona), Spain,