Pyroelectric conversion: Harvesting Energy from Temperature Fluctuations Dr. Àngel Cuadras Instrumentation, Sensors and Interfaces Group Castelldefels School of Technology Universitat Politècnica de Catalunya (UPC) 1
COLLABORATIONS • University of Brescia. (Dept. Electronics for Automation and INFM) – A. Ghisla, V. Ferrari, M. Ferrari
• Instrumentation, Sensors and Interfaces Group Castelldefels School of Technology – Dr. Gasulla, Dr. Pallàs
2
INTRODUCTION Thermal energy •Present everywhere •Thermodynamical restrictions Sun Fire
Sources
Industry Hot Pipes Engines
Thermal to electrical conversion – Thermoelectricity: thermal gradients – Pyroelectricity: from thermal time-dependent fluctuations 3
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… 5
PHYSICAL DESCRIPTION • Crystalline structures
∆
Cations (Pb,Ti,Ca,Ta…) Anions (O)
Cubic structure 6
PHYSICAL DESCRIPTION • Crystalline structures • Point symmetry
Cations (Pb,Ti,Ca,Ta…) Anions (O)
Tetragonal structure 7
PHYSICAL DESCRIPTION • Crystalline structures • Point symmetry
•Mechanical stress Structure Deformation ∆
•Thermal stress •Electrical stress
Piezoelectric Pyroelectric Ferroelectric Tetragonal structure 8
PHYSICAL DESCRIPTION • Crystalline structures • Point symmetry
•Mechanical stress Structure Deformation ∆
•Thermal stress •Electrical stress
Pyroelectric
Tetragonal structure 9
PHYSICAL DESCRIPTION • Crystalline structures • Point symmetry
•Mechanical stress Structure Deformation ∆
•Thermal stress •Electrical stress
∆ ∆T
+++++++++++++++++++++ ∆V Pyroelectric --------------------
Tetragonal structure
Ion displacement due to ∆T Æ Induced charge 10
PHYSICAL DESCRIPTION • Crystalline structures • Point symmetry
•Mechanical stress Structure Deformation ∆
•Thermal stress •Electrical stress
T>TC Paraelectric
Cubic structure
Ion symmetry Æ no induced charge 11
PYROELECTRIC EFFECT •Temperature increase TGS
•Polarization 0
•Dependence of p on T ps =
250
150
-4
p P
100
-15
-2
-10
P(µC m )
200
-2
-1
p (10 C m K )
-5
dPs dT
•Maximum temperature Æ Curie temperature, phase transition
-20
50 TCurie
0 300
305 T (K)
310
-25 315
•Induced current as a function of T I=
dQs dPs dT = = Sps dt dt dt
12
PYROELECTRIC MATERIALS • Crystal materials – CaTiO3,LiTaO3,PbTiO3 – Triglycine sulfate (TGS) – Growth methods: Czochralki, water dissolution
• Ceramics – PZT - Lead zirconate titanate – Growth methods: Screen printing – Poling
LiTaO3
• Polymers – PVDF-Polyvinylidene Difluoride – Growth methods: Chemical processing TGS 13
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 p FoM = cV ε 0 ε r Material
p (10-4 C m-2 K-1)
TGS
εr (1 kHz)
TC (ºC)
cv (J cm-3 K-1)
3.5
35
49
2.5
LiTaO3
2.3
46
665
3.2
PZT
1.6
1350
320
PVDF
0.3
12
80
2.4 14
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 16
APPLICATIONS: HARVESTERS
R. B. Olsen, D. A. Bruno, and J. M. Briscoe, "Pyroelectric Conversion Cycles," J. Appl. Phys. 58 (1985) 4709 17
PYROELECTRICITY: YES OR NOT? YES?
NOT? • Low power generation • Low conversion efficiency • Temperature fluctuations
• Low cost • Infinite thermal sources
Estimation: S = 10 cm2 λ= 10-4 C m-2K-1
⇒
I = 1 µA
dT/dt= 10 K s-1 18
MODELING CONVERSION I = S · p·
W
RT
CT
T
I
Thermal model
dT dt Re
Ce
V ∆V =
S ·p ·∆T Ce
Electrical model
Harvester critical parameters RT and CT : thermal conductivity and thermal capacitance Re and Ce : electrical losses and electrical capacitance Efficiency (< 1 %) 19
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
Thermal measurement •SMD Thermistor •Fast thermal response •Sensitivity up to 0.01 K
Current Measurement Rf I VO
Acquisition System Agilent
Voltage measurement Electrometer Keithley 616
Resistance measurement Electrometer Keithley 616 R up to 1014 Ω 21
PZT STUDIED HARVESTERS 4 cm
4 cm
Technology
PZT
•Ceramic powder
Alumina Substrate
•Screen printing. •Firing •Poling
Bottom electrode PdAg (contact)
Sample ID
Target Thickness (µm)
Poling Field (MV/m)
1
60
5
2
60
7
3
100
5
4
100
7
22
PZT FORMATION Tpoling + -
Random orientation of dipoles
DC field application: poling
Remanent polarization
Dipole orientation
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PZT CONVERTERS dT/dt (K/s)
I T dT/dt
0,3
I (µA)
0,2
T (K) 350
1,0
340
• Step function
0,5
330
• Large thermal inertia
0,0
320
Pyrocurrent follows dT/dt
0,1 0,0 310 -0,5
-0,1 0
50
100
150 Time (s)
200
250
Air Heating:
300 300
Imax = 0.3 mA
Generated charge density Q = 0.75 C·cm-2 24
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 25
PZT CONVERTERS 1 3
Constant poling field 5 MV/m
0.3
Technological dependence:
I (µA)
0.2
• Poling Field 0.1
• Thickness
0.0
Optimized design
-0.1 0
20
40 60 Time (s)
80
100
26
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
27
PVDF CONVERTERS 0.4
0.0
•
Warm air flow/fan
•
Temperature fluctuation (298 K Æ 335 K)
-2
-0.2
3.60 cm
-2
7.44 cm -0.4 0
10
20
4
30 40 Time (s)
50
•
Peak current
•
Generated Charge density
60
Q = 0.24 C·cm-2 •
3 dT/dt (K/s)
I (µA)
0.2
2
Symmetry in heating and cooling
1 0 0
10
20
T im e ( s )
30
28
IMPROVING HARVESTERS
• Cell association • Energy storage • Thermal cycling
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PARALLEL ASSOCIATION Parallel Cell Association
0,4 3 4 3||4
I (µA)
0,3
0,2
Current addition
0,1
0,0 0
25
50 time (s)
75
100
Stacked structures 30
ENERGY STORAGE
Ce
•Impedance matching overcome •Low power systems strategy •Rectification + storage
•Energy loss at diodes •Capacitor charge 31
THERMAL CYCLING
10
6 330
V (V)
8 320
6 4
310
2
340
T (K)
330
5 4
320
3 310
2 1
300
V (V) 0 0
50
300 100 150 200 250 300 350
0 0
100
time (s) N ⎡ ⎛ ⎞ QS CL − Ce ⎤ S·p·∆T ⎢1 − ⎜ Vo ( N ) = ⎟ ⎥= 2Ce ⎢ ⎝ CL + Ce ⎠ ⎥ 2Ce ⎣ ⎦
Temperature (K)
12
V(V)
V T
PVDF
340
Temperature (K)
PZT
⎡ ⎛ C − C ⎞N ⎤ e ⎢1 − ⎜ L ⎟ ⎥ ⎢⎣ ⎝ CL + Ce ⎠ ⎥⎦
200
300 Time (s)
400
500
Vo,max ( N → ∞ ) =
S·p·∆T 2Ce 32
BEYOND PYROELECTRICITY 0,3
I T
360
I (µA)
0,1
340
0,0
320
-0,1 -0,2 -0,3
300 0
100
200 Time (s)
300
Temperature (K)
0,2
•Materials sensitive to external influences. •Generated current from a PZT when illuminated. •Current is not proportional to dT/dt.
400
•Combination of different effects in a single harvester •Piezoelectrical response – when undergo mechanical stresses •Semiconductor – heated with light 33
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?
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[email protected]
Castelldefels School of Technology (EPSC), Universitat Politècnica de Catalunya (UPC) 35